pigpio/pigpio.py

"""
pigpio is a Python module for the Raspberry which talks to
the pigpio daemon to allow control of the general purpose
input outputs (GPIO).

[http://abyz.me.uk/rpi/pigpio/python.html]

*Features*

o the pigpio Python module can run on Windows, Macs, or Linux

o controls one or more Pi's

o hardware timed PWM on any of GPIO 0-31

o hardware timed servo pulses on any of GPIO 0-31

o callbacks when any of GPIO 0-31 change state

o creating and transmitting precisely timed waveforms

o reading/writing GPIO and setting their modes

o wrappers for I2C, SPI, and serial links

o creating and running scripts on the pigpio daemon

*GPIO*

ALL GPIO are identified by their Broadcom number.

*Notes*

Transmitted waveforms are accurate to a microsecond.

Callback level changes are time-stamped and will be
accurate to within a few microseconds.

*Settings*

A number of settings are determined when the pigpio daemon is started.

o the sample rate (1, 2, 4, 5, 8, or 10 us, default 5 us).

o the set of GPIO which may be updated (generally written to).  The
  default set is those available on the Pi board revision.

o the available PWM frequencies (see [*set_PWM_frequency*]).

*Exceptions*

By default a fatal exception is raised if you pass an invalid
argument to a pigpio function.

If you wish to handle the returned status yourself you should set
pigpio.exceptions to False.

You may prefer to check the returned status in only a few parts
of your code.  In that case do the following:

...
pigpio.exceptions = False

# Code where you want to test the error status.

pigpio.exceptions = True
...

*Usage*

This module uses the services of the C pigpio library.  pigpio
must be running on the Pi(s) whose GPIO are to be manipulated.

The normal way to start pigpio is as a daemon (during system
start).

sudo pigpiod

Your Python program must import pigpio and create one or more
instances of the pigpio.pi class.  This class gives access to
a specified Pi's GPIO.

...
pi1 = pigpio.pi()       # pi1 accesses the local Pi's GPIO
pi2 = pigpio.pi('tom')  # pi2 accesses tom's GPIO
pi3 = pigpio.pi('dick') # pi3 accesses dick's GPIO

pi1.write(4, 0) # set local Pi's GPIO 4 low
pi2.write(4, 1) # set tom's GPIO 4 to high
pi3.read(4)     # get level of dick's GPIO 4
...

The later example code snippets assume that pi is an instance of
the pigpio.pi class.

OVERVIEW

Essential

pigpio.pi                 Initialise Pi connection
stop                      Stop a Pi connection

Beginner

set_mode                  Set a GPIO mode
get_mode                  Get a GPIO mode
set_pull_up_down          Set/clear GPIO pull up/down resistor

read                      Read a GPIO
write                     Write a GPIO

set_PWM_dutycycle         Start/stop PWM pulses on a GPIO
get_PWM_dutycycle         Get PWM dutycycle set on a GPIO

set_servo_pulsewidth      Start/Stop servo pulses on a GPIO
get_servo_pulsewidth      Get servo pulsewidth set on a GPIO

callback                  Create GPIO level change callback
wait_for_edge             Wait for GPIO level change

Intermediate

gpio_trigger              Send a trigger pulse to a GPIO

set_watchdog              Set a watchdog on a GPIO

set_PWM_range             Configure PWM range of a GPIO
get_PWM_range             Get configured PWM range of a GPIO

set_PWM_frequency         Set PWM frequency of a GPIO
get_PWM_frequency         Get PWM frequency of a GPIO

read_bank_1               Read all bank 1 GPIO
read_bank_2               Read all bank 2 GPIO

clear_bank_1              Clear selected GPIO in bank 1
clear_bank_2              Clear selected GPIO in bank 2

set_bank_1                Set selected GPIO in bank 1
set_bank_2                Set selected GPIO in bank 2

Advanced

get_PWM_real_range        Get underlying PWM range for a GPIO

notify_open               Request a notification handle
notify_begin              Start notifications for selected GPIO
notify_pause              Pause notifications
notify_close              Close a notification

bb_serial_read_open       Open a GPIO for bit bang serial reads
bb_serial_read            Read bit bang serial data from  a GPIO
bb_serial_read_close      Close a GPIO for bit bang serial reads
bb_serial_invert          Invert serial logic (1 invert, 0 normal)

hardware_clock            Start hardware clock on supported GPIO
hardware_PWM              Start hardware PWM on supported GPIO

set_glitch_filter         Set a glitch filter on a GPIO
set_noise_filter          Set a noise filter on a GPIO

get_pad_strength          Gets a pads drive strength
set_pad_strength          Sets a pads drive strength

shell                     Executes a shell command

Scripts

store_script              Store a script
run_script                Run a stored script
script_status             Get script status and parameters
stop_script               Stop a running script
delete_script             Delete a stored script

Waves

wave_clear                Deletes all waveforms

wave_add_new              Starts a new waveform
wave_add_generic          Adds a series of pulses to the waveform
wave_add_serial           Adds serial data to the waveform

wave_create               Creates a waveform from added data
wave_delete               Deletes a waveform

wave_send_once            Transmits a waveform once
wave_send_repeat          Transmits a waveform repeatedly
wave_send_using_mode      Transmits a waveform in the chosen mode

wave_chain                Transmits a chain of waveforms

wave_tx_at                Returns the current transmitting waveform
wave_tx_busy              Checks to see if a waveform has ended
wave_tx_stop              Aborts the current waveform

wave_get_micros           Length in microseconds of the current waveform
wave_get_max_micros       Absolute maximum allowed micros
wave_get_pulses           Length in pulses of the current waveform
wave_get_max_pulses       Absolute maximum allowed pulses
wave_get_cbs              Length in cbs of the current waveform
wave_get_max_cbs          Absolute maximum allowed cbs

I2C

i2c_open                  Opens an I2C device
i2c_close                 Closes an I2C device

i2c_write_quick           SMBus write quick
i2c_write_byte            SMBus write byte
i2c_read_byte             SMBus read byte
i2c_write_byte_data       SMBus write byte data
i2c_write_word_data       SMBus write word data
i2c_read_byte_data        SMBus read byte data
i2c_read_word_data        SMBus read word data
i2c_process_call          SMBus process call
i2c_write_block_data      SMBus write block data
i2c_read_block_data       SMBus read block data
i2c_block_process_call    SMBus block process call

i2c_read_i2c_block_data   SMBus read I2C block data
i2c_write_i2c_block_data  SMBus write I2C block data

i2c_read_device           Reads the raw I2C device
i2c_write_device          Writes the raw I2C device

i2c_zip                   Performs multiple I2C transactions

bb_i2c_open               Opens GPIO for bit banging I2C
bb_i2c_close              Closes GPIO for bit banging I2C
bb_i2c_zip                Performs multiple bit banged I2C transactions

SPI

spi_open                  Opens a SPI device
spi_close                 Closes a SPI device

spi_read                  Reads bytes from a SPI device
spi_write                 Writes bytes to a SPI device
spi_xfer                  Transfers bytes with a SPI device

bb_spi_open               Opens GPIO for bit banging SPI
bb_spi_close              Closes GPIO for bit banging SPI
bb_spi_xfer               Transfers bytes with bit banging SPI

I2C/SPI_Slave

bsc_xfer                  I2C/SPI as slave transfer
bsc_i2c                   I2C as slave transfer

Serial

serial_open               Opens a serial device
serial_close              Closes a serial device

serial_read               Reads bytes from a serial device
serial_read_byte          Reads a byte from a serial device

serial_write              Writes bytes to a serial device
serial_write_byte         Writes a byte to a serial device

serial_data_available     Returns number of bytes ready to be read

Files

file_open                 Opens a file
file_close                Closes a file
file_read                 Reads bytes from a file
file_write                Writes bytes to a file
file_seek                 Seeks to a position within a file
file_list                 List files which match a pattern

Events

event_callback            Sets a callback for an event
event_trigger             Triggers an event
wait_for_event            Wait for an event

Custom

custom_1                  User custom function 1
custom_2                  User custom function 2

Utility

get_current_tick          Get current tick (microseconds)

get_hardware_revision     Get hardware revision
get_pigpio_version        Get the pigpio version

pigpio.error_text         Gets error text from error number
pigpio.tickDiff           Returns difference between two ticks
"""

import sys
import socket
import struct
import time
import threading
import os
import atexit

VERSION = "1.39"

exceptions = True

# GPIO levels

OFF   = 0
LOW   = 0
CLEAR = 0

ON   = 1
HIGH = 1
SET  = 1

TIMEOUT = 2

# GPIO edges

RISING_EDGE  = 0
FALLING_EDGE = 1
EITHER_EDGE  = 2

# GPIO modes

INPUT  = 0
OUTPUT = 1
ALT0   = 4
ALT1   = 5
ALT2   = 6
ALT3   = 7
ALT4   = 3
ALT5   = 2

# GPIO Pull Up Down

PUD_OFF  = 0
PUD_DOWN = 1
PUD_UP   = 2

# script run status

PI_SCRIPT_INITING=0
PI_SCRIPT_HALTED =1
PI_SCRIPT_RUNNING=2
PI_SCRIPT_WAITING=3
PI_SCRIPT_FAILED =4

# notification flags

NTFY_FLAGS_EVENT = (1 << 7)
NTFY_FLAGS_ALIVE = (1 << 6)
NTFY_FLAGS_WDOG  = (1 << 5)
NTFY_FLAGS_GPIO  = 31

# wave modes

WAVE_MODE_ONE_SHOT     =0
WAVE_MODE_REPEAT       =1
WAVE_MODE_ONE_SHOT_SYNC=2
WAVE_MODE_REPEAT_SYNC  =3

WAVE_NOT_FOUND = 9998 # Transmitted wave not found.
NO_TX_WAVE     = 9999 # No wave being transmitted.

FILE_READ=1
FILE_WRITE=2
FILE_RW=3

FILE_APPEND=4
FILE_CREATE=8
FILE_TRUNC=16

FROM_START=0
FROM_CURRENT=1
FROM_END=2

SPI_MODE_0 = 0
SPI_MODE_1 = 1
SPI_MODE_2 = 2
SPI_MODE_3 = 3

SPI_CPHA = 1 << 0
SPI_CPOL = 1 << 1

SPI_CS_HIGH_ACTIVE  = 1 << 2

SPI_TX_LSBFIRST = 1 << 14
SPI_RX_LSBFIRST = 1 << 15

EVENT_BSC = 31

_SOCK_CMD_LEN = 16

# pigpio command numbers

_PI_CMD_MODES= 0
_PI_CMD_MODEG= 1
_PI_CMD_PUD=   2
_PI_CMD_READ=  3
_PI_CMD_WRITE= 4
_PI_CMD_PWM=   5
_PI_CMD_PRS=   6
_PI_CMD_PFS=   7
_PI_CMD_SERVO= 8
_PI_CMD_WDOG=  9
_PI_CMD_BR1=  10
_PI_CMD_BR2=  11
_PI_CMD_BC1=  12
_PI_CMD_BC2=  13
_PI_CMD_BS1=  14
_PI_CMD_BS2=  15
_PI_CMD_TICK= 16
_PI_CMD_HWVER=17

_PI_CMD_NO=   18
_PI_CMD_NB=   19
_PI_CMD_NP=   20
_PI_CMD_NC=   21

_PI_CMD_PRG=  22
_PI_CMD_PFG=  23
_PI_CMD_PRRG= 24
_PI_CMD_HELP= 25
_PI_CMD_PIGPV=26

_PI_CMD_WVCLR=27
_PI_CMD_WVAG= 28
_PI_CMD_WVAS= 29
_PI_CMD_WVGO= 30
_PI_CMD_WVGOR=31
_PI_CMD_WVBSY=32
_PI_CMD_WVHLT=33
_PI_CMD_WVSM= 34
_PI_CMD_WVSP= 35
_PI_CMD_WVSC= 36

_PI_CMD_TRIG= 37

_PI_CMD_PROC= 38
_PI_CMD_PROCD=39
_PI_CMD_PROCR=40
_PI_CMD_PROCS=41

_PI_CMD_SLRO= 42
_PI_CMD_SLR=  43
_PI_CMD_SLRC= 44

_PI_CMD_PROCP=45
_PI_CMD_MICRO=46
_PI_CMD_MILLI=47
_PI_CMD_PARSE=48

_PI_CMD_WVCRE=49
_PI_CMD_WVDEL=50
_PI_CMD_WVTX =51
_PI_CMD_WVTXR=52
_PI_CMD_WVNEW=53

_PI_CMD_I2CO =54
_PI_CMD_I2CC =55
_PI_CMD_I2CRD=56
_PI_CMD_I2CWD=57
_PI_CMD_I2CWQ=58
_PI_CMD_I2CRS=59
_PI_CMD_I2CWS=60
_PI_CMD_I2CRB=61
_PI_CMD_I2CWB=62
_PI_CMD_I2CRW=63
_PI_CMD_I2CWW=64
_PI_CMD_I2CRK=65
_PI_CMD_I2CWK=66
_PI_CMD_I2CRI=67
_PI_CMD_I2CWI=68
_PI_CMD_I2CPC=69
_PI_CMD_I2CPK=70

_PI_CMD_SPIO =71
_PI_CMD_SPIC =72
_PI_CMD_SPIR =73
_PI_CMD_SPIW =74
_PI_CMD_SPIX =75

_PI_CMD_SERO =76
_PI_CMD_SERC =77
_PI_CMD_SERRB=78
_PI_CMD_SERWB=79
_PI_CMD_SERR =80
_PI_CMD_SERW =81
_PI_CMD_SERDA=82

_PI_CMD_GDC  =83
_PI_CMD_GPW  =84

_PI_CMD_HC   =85
_PI_CMD_HP   =86

_PI_CMD_CF1  =87
_PI_CMD_CF2  =88

_PI_CMD_NOIB =99

_PI_CMD_BI2CC=89
_PI_CMD_BI2CO=90
_PI_CMD_BI2CZ=91

_PI_CMD_I2CZ =92

_PI_CMD_WVCHA=93

_PI_CMD_SLRI =94

_PI_CMD_CGI  =95
_PI_CMD_CSI  =96

_PI_CMD_FG   =97
_PI_CMD_FN   =98

_PI_CMD_WVTXM=100
_PI_CMD_WVTAT=101

_PI_CMD_PADS =102
_PI_CMD_PADG =103

_PI_CMD_FO   =104
_PI_CMD_FC   =105
_PI_CMD_FR   =106
_PI_CMD_FW   =107
_PI_CMD_FS   =108
_PI_CMD_FL   =109
_PI_CMD_SHELL=110

_PI_CMD_BSPIC=111
_PI_CMD_BSPIO=112
_PI_CMD_BSPIX=113

_PI_CMD_BSCX =114

_PI_CMD_EVM  =115
_PI_CMD_EVT  =116

# pigpio error numbers

_PI_INIT_FAILED     =-1
PI_BAD_USER_GPIO    =-2
PI_BAD_GPIO         =-3
PI_BAD_MODE         =-4
PI_BAD_LEVEL        =-5
PI_BAD_PUD          =-6
PI_BAD_PULSEWIDTH   =-7
PI_BAD_DUTYCYCLE    =-8
_PI_BAD_TIMER       =-9
_PI_BAD_MS          =-10
_PI_BAD_TIMETYPE    =-11
_PI_BAD_SECONDS     =-12
_PI_BAD_MICROS      =-13
_PI_TIMER_FAILED    =-14
PI_BAD_WDOG_TIMEOUT =-15
_PI_NO_ALERT_FUNC   =-16
_PI_BAD_CLK_PERIPH  =-17
_PI_BAD_CLK_SOURCE  =-18
_PI_BAD_CLK_MICROS  =-19
_PI_BAD_BUF_MILLIS  =-20
PI_BAD_DUTYRANGE    =-21
_PI_BAD_SIGNUM      =-22
_PI_BAD_PATHNAME    =-23
PI_NO_HANDLE        =-24
PI_BAD_HANDLE       =-25
_PI_BAD_IF_FLAGS    =-26
_PI_BAD_CHANNEL     =-27
_PI_BAD_PRIM_CHANNEL=-27
_PI_BAD_SOCKET_PORT =-28
_PI_BAD_FIFO_COMMAND=-29
_PI_BAD_SECO_CHANNEL=-30
_PI_NOT_INITIALISED =-31
_PI_INITIALISED     =-32
_PI_BAD_WAVE_MODE   =-33
_PI_BAD_CFG_INTERNAL=-34
PI_BAD_WAVE_BAUD    =-35
PI_TOO_MANY_PULSES  =-36
PI_TOO_MANY_CHARS   =-37
PI_NOT_SERIAL_GPIO  =-38
_PI_BAD_SERIAL_STRUC=-39
_PI_BAD_SERIAL_BUF  =-40
PI_NOT_PERMITTED    =-41
PI_SOME_PERMITTED   =-42
PI_BAD_WVSC_COMMND  =-43
PI_BAD_WVSM_COMMND  =-44
PI_BAD_WVSP_COMMND  =-45
PI_BAD_PULSELEN     =-46
PI_BAD_SCRIPT       =-47
PI_BAD_SCRIPT_ID    =-48
PI_BAD_SER_OFFSET   =-49
PI_GPIO_IN_USE      =-50
PI_BAD_SERIAL_COUNT =-51
PI_BAD_PARAM_NUM    =-52
PI_DUP_TAG          =-53
PI_TOO_MANY_TAGS    =-54
PI_BAD_SCRIPT_CMD   =-55
PI_BAD_VAR_NUM      =-56
PI_NO_SCRIPT_ROOM   =-57
PI_NO_MEMORY        =-58
PI_SOCK_READ_FAILED =-59
PI_SOCK_WRIT_FAILED =-60
PI_TOO_MANY_PARAM   =-61
PI_SCRIPT_NOT_READY =-62
PI_BAD_TAG          =-63
PI_BAD_MICS_DELAY   =-64
PI_BAD_MILS_DELAY   =-65
PI_BAD_WAVE_ID      =-66
PI_TOO_MANY_CBS     =-67
PI_TOO_MANY_OOL     =-68
PI_EMPTY_WAVEFORM   =-69
PI_NO_WAVEFORM_ID   =-70
PI_I2C_OPEN_FAILED  =-71
PI_SER_OPEN_FAILED  =-72
PI_SPI_OPEN_FAILED  =-73
PI_BAD_I2C_BUS      =-74
PI_BAD_I2C_ADDR     =-75
PI_BAD_SPI_CHANNEL  =-76
PI_BAD_FLAGS        =-77
PI_BAD_SPI_SPEED    =-78
PI_BAD_SER_DEVICE   =-79
PI_BAD_SER_SPEED    =-80
PI_BAD_PARAM        =-81
PI_I2C_WRITE_FAILED =-82
PI_I2C_READ_FAILED  =-83
PI_BAD_SPI_COUNT    =-84
PI_SER_WRITE_FAILED =-85
PI_SER_READ_FAILED  =-86
PI_SER_READ_NO_DATA =-87
PI_UNKNOWN_COMMAND  =-88
PI_SPI_XFER_FAILED  =-89
_PI_BAD_POINTER     =-90
PI_NO_AUX_SPI       =-91
PI_NOT_PWM_GPIO     =-92
PI_NOT_SERVO_GPIO   =-93
PI_NOT_HCLK_GPIO    =-94
PI_NOT_HPWM_GPIO    =-95
PI_BAD_HPWM_FREQ    =-96
PI_BAD_HPWM_DUTY    =-97
PI_BAD_HCLK_FREQ    =-98
PI_BAD_HCLK_PASS    =-99
PI_HPWM_ILLEGAL     =-100
PI_BAD_DATABITS     =-101
PI_BAD_STOPBITS     =-102
PI_MSG_TOOBIG       =-103
PI_BAD_MALLOC_MODE  =-104
_PI_TOO_MANY_SEGS   =-105
_PI_BAD_I2C_SEG     =-106
PI_BAD_SMBUS_CMD    =-107
PI_NOT_I2C_GPIO     =-108
PI_BAD_I2C_WLEN     =-109
PI_BAD_I2C_RLEN     =-110
PI_BAD_I2C_CMD      =-111
PI_BAD_I2C_BAUD     =-112
PI_CHAIN_LOOP_CNT   =-113
PI_BAD_CHAIN_LOOP   =-114
PI_CHAIN_COUNTER    =-115
PI_BAD_CHAIN_CMD    =-116
PI_BAD_CHAIN_DELAY  =-117
PI_CHAIN_NESTING    =-118
PI_CHAIN_TOO_BIG    =-119
PI_DEPRECATED       =-120
PI_BAD_SER_INVERT   =-121
_PI_BAD_EDGE        =-122
_PI_BAD_ISR_INIT    =-123
PI_BAD_FOREVER      =-124
PI_BAD_FILTER       =-125
PI_BAD_PAD          =-126
PI_BAD_STRENGTH     =-127
PI_FIL_OPEN_FAILED  =-128
PI_BAD_FILE_MODE    =-129
PI_BAD_FILE_FLAG    =-130
PI_BAD_FILE_READ    =-131
PI_BAD_FILE_WRITE   =-132
PI_FILE_NOT_ROPEN   =-133
PI_FILE_NOT_WOPEN   =-134
PI_BAD_FILE_SEEK    =-135
PI_NO_FILE_MATCH    =-136
PI_NO_FILE_ACCESS   =-137
PI_FILE_IS_A_DIR    =-138
PI_BAD_SHELL_STATUS =-139
PI_BAD_SCRIPT_NAME  =-140
PI_BAD_SPI_BAUD     =-141
PI_NOT_SPI_GPIO     =-142
PI_BAD_EVENT_ID     =-143

# pigpio error text

_errors=[
   [_PI_INIT_FAILED      , "pigpio initialisation failed"],
   [PI_BAD_USER_GPIO     , "GPIO not 0-31"],
   [PI_BAD_GPIO          , "GPIO not 0-53"],
   [PI_BAD_MODE          , "mode not 0-7"],
   [PI_BAD_LEVEL         , "level not 0-1"],
   [PI_BAD_PUD           , "pud not 0-2"],
   [PI_BAD_PULSEWIDTH    , "pulsewidth not 0 or 500-2500"],
   [PI_BAD_DUTYCYCLE     , "dutycycle not 0-range (default 255)"],
   [_PI_BAD_TIMER        , "timer not 0-9"],
   [_PI_BAD_MS           , "ms not 10-60000"],
   [_PI_BAD_TIMETYPE     , "timetype not 0-1"],
   [_PI_BAD_SECONDS      , "seconds < 0"],
   [_PI_BAD_MICROS       , "micros not 0-999999"],
   [_PI_TIMER_FAILED     , "gpioSetTimerFunc failed"],
   [PI_BAD_WDOG_TIMEOUT  , "timeout not 0-60000"],
   [_PI_NO_ALERT_FUNC    , "DEPRECATED"],
   [_PI_BAD_CLK_PERIPH   , "clock peripheral not 0-1"],
   [_PI_BAD_CLK_SOURCE   , "DEPRECATED"],
   [_PI_BAD_CLK_MICROS   , "clock micros not 1, 2, 4, 5, 8, or 10"],
   [_PI_BAD_BUF_MILLIS   , "buf millis not 100-10000"],
   [PI_BAD_DUTYRANGE     , "dutycycle range not 25-40000"],
   [_PI_BAD_SIGNUM       , "signum not 0-63"],
   [_PI_BAD_PATHNAME     , "can't open pathname"],
   [PI_NO_HANDLE         , "no handle available"],
   [PI_BAD_HANDLE        , "unknown handle"],
   [_PI_BAD_IF_FLAGS     , "ifFlags > 4"],
   [_PI_BAD_CHANNEL      , "DMA channel not 0-14"],
   [_PI_BAD_SOCKET_PORT  , "socket port not 1024-30000"],
   [_PI_BAD_FIFO_COMMAND , "unknown fifo command"],
   [_PI_BAD_SECO_CHANNEL , "DMA secondary channel not 0-14"],
   [_PI_NOT_INITIALISED  , "function called before gpioInitialise"],
   [_PI_INITIALISED      , "function called after gpioInitialise"],
   [_PI_BAD_WAVE_MODE    , "waveform mode not 0-1"],
   [_PI_BAD_CFG_INTERNAL , "bad parameter in gpioCfgInternals call"],
   [PI_BAD_WAVE_BAUD     , "baud rate not 50-250000(RX)/1000000(TX)"],
   [PI_TOO_MANY_PULSES   , "waveform has too many pulses"],
   [PI_TOO_MANY_CHARS    , "waveform has too many chars"],
   [PI_NOT_SERIAL_GPIO   , "no bit bang serial read in progress on GPIO"],
   [PI_NOT_PERMITTED     , "no permission to update GPIO"],
   [PI_SOME_PERMITTED    , "no permission to update one or more GPIO"],
   [PI_BAD_WVSC_COMMND   , "bad WVSC subcommand"],
   [PI_BAD_WVSM_COMMND   , "bad WVSM subcommand"],
   [PI_BAD_WVSP_COMMND   , "bad WVSP subcommand"],
   [PI_BAD_PULSELEN      , "trigger pulse length not 1-100"],
   [PI_BAD_SCRIPT        , "invalid script"],
   [PI_BAD_SCRIPT_ID     , "unknown script id"],
   [PI_BAD_SER_OFFSET    , "add serial data offset > 30 minute"],
   [PI_GPIO_IN_USE       , "GPIO already in use"],
   [PI_BAD_SERIAL_COUNT  , "must read at least a byte at a time"],
   [PI_BAD_PARAM_NUM     , "script parameter id not 0-9"],
   [PI_DUP_TAG           , "script has duplicate tag"],
   [PI_TOO_MANY_TAGS     , "script has too many tags"],
   [PI_BAD_SCRIPT_CMD    , "illegal script command"],
   [PI_BAD_VAR_NUM       , "script variable id not 0-149"],
   [PI_NO_SCRIPT_ROOM    , "no more room for scripts"],
   [PI_NO_MEMORY         , "can't allocate temporary memory"],
   [PI_SOCK_READ_FAILED  , "socket read failed"],
   [PI_SOCK_WRIT_FAILED  , "socket write failed"],
   [PI_TOO_MANY_PARAM    , "too many script parameters (> 10)"],
   [PI_SCRIPT_NOT_READY  , "script initialising"],
   [PI_BAD_TAG           , "script has unresolved tag"],
   [PI_BAD_MICS_DELAY    , "bad MICS delay (too large)"],
   [PI_BAD_MILS_DELAY    , "bad MILS delay (too large)"],
   [PI_BAD_WAVE_ID       , "non existent wave id"],
   [PI_TOO_MANY_CBS      , "No more CBs for waveform"],
   [PI_TOO_MANY_OOL      , "No more OOL for waveform"],
   [PI_EMPTY_WAVEFORM    , "attempt to create an empty waveform"],
   [PI_NO_WAVEFORM_ID    , "No more waveform ids"],
   [PI_I2C_OPEN_FAILED   , "can't open I2C device"],
   [PI_SER_OPEN_FAILED   , "can't open serial device"],
   [PI_SPI_OPEN_FAILED   , "can't open SPI device"],
   [PI_BAD_I2C_BUS       , "bad I2C bus"],
   [PI_BAD_I2C_ADDR      , "bad I2C address"],
   [PI_BAD_SPI_CHANNEL   , "bad SPI channel"],
   [PI_BAD_FLAGS         , "bad i2c/spi/ser open flags"],
   [PI_BAD_SPI_SPEED     , "bad SPI speed"],
   [PI_BAD_SER_DEVICE    , "bad serial device name"],
   [PI_BAD_SER_SPEED     , "bad serial baud rate"],
   [PI_BAD_PARAM         , "bad i2c/spi/ser parameter"],
   [PI_I2C_WRITE_FAILED  , "I2C write failed"],
   [PI_I2C_READ_FAILED   , "I2C read failed"],
   [PI_BAD_SPI_COUNT     , "bad SPI count"],
   [PI_SER_WRITE_FAILED  , "ser write failed"],
   [PI_SER_READ_FAILED   , "ser read failed"],
   [PI_SER_READ_NO_DATA  , "ser read no data available"],
   [PI_UNKNOWN_COMMAND   , "unknown command"],
   [PI_SPI_XFER_FAILED   , "SPI xfer/read/write failed"],
   [_PI_BAD_POINTER      , "bad (NULL) pointer"],
   [PI_NO_AUX_SPI        , "no auxiliary SPI on Pi A or B"],
   [PI_NOT_PWM_GPIO      , "GPIO is not in use for PWM"],
   [PI_NOT_SERVO_GPIO    , "GPIO is not in use for servo pulses"],
   [PI_NOT_HCLK_GPIO     , "GPIO has no hardware clock"],
   [PI_NOT_HPWM_GPIO     , "GPIO has no hardware PWM"],
   [PI_BAD_HPWM_FREQ     , "hardware PWM frequency not 1-125M"],
   [PI_BAD_HPWM_DUTY     , "hardware PWM dutycycle not 0-1M"],
   [PI_BAD_HCLK_FREQ     , "hardware clock frequency not 4689-250M"],
   [PI_BAD_HCLK_PASS     , "need password to use hardware clock 1"],
   [PI_HPWM_ILLEGAL      , "illegal, PWM in use for main clock"],
   [PI_BAD_DATABITS      , "serial data bits not 1-32"],
   [PI_BAD_STOPBITS      , "serial (half) stop bits not 2-8"],
   [PI_MSG_TOOBIG        , "socket/pipe message too big"],
   [PI_BAD_MALLOC_MODE   , "bad memory allocation mode"],
   [_PI_TOO_MANY_SEGS    , "too many I2C transaction segments"],
   [_PI_BAD_I2C_SEG      , "an I2C transaction segment failed"],
   [PI_BAD_SMBUS_CMD     , "SMBus command not supported"],
   [PI_NOT_I2C_GPIO      , "no bit bang I2C in progress on GPIO"],
   [PI_BAD_I2C_WLEN      , "bad I2C write length"],
   [PI_BAD_I2C_RLEN      , "bad I2C read length"],
   [PI_BAD_I2C_CMD       , "bad I2C command"],
   [PI_BAD_I2C_BAUD      , "bad I2C baud rate, not 50-500k"],
   [PI_CHAIN_LOOP_CNT    , "bad chain loop count"],
   [PI_BAD_CHAIN_LOOP    , "empty chain loop"],
   [PI_CHAIN_COUNTER     , "too many chain counters"],
   [PI_BAD_CHAIN_CMD     , "bad chain command"],
   [PI_BAD_CHAIN_DELAY   , "bad chain delay micros"],
   [PI_CHAIN_NESTING     , "chain counters nested too deeply"],
   [PI_CHAIN_TOO_BIG     , "chain is too long"],
   [PI_DEPRECATED        , "deprecated function removed"],
   [PI_BAD_SER_INVERT    , "bit bang serial invert not 0 or 1"],
   [_PI_BAD_EDGE         , "bad ISR edge value, not 0-2"],
   [_PI_BAD_ISR_INIT     , "bad ISR initialisation"],
   [PI_BAD_FOREVER       , "loop forever must be last chain command"],
   [PI_BAD_FILTER        , "bad filter parameter"],
   [PI_BAD_PAD           , "bad pad number"],
   [PI_BAD_STRENGTH      , "bad pad drive strength"],
   [PI_FIL_OPEN_FAILED   , "file open failed"],
   [PI_BAD_FILE_MODE     , "bad file mode"],
   [PI_BAD_FILE_FLAG     , "bad file flag"],
   [PI_BAD_FILE_READ     , "bad file read"],
   [PI_BAD_FILE_WRITE    , "bad file write"],
   [PI_FILE_NOT_ROPEN    , "file not open for read"],
   [PI_FILE_NOT_WOPEN    , "file not open for write"],
   [PI_BAD_FILE_SEEK     , "bad file seek"],
   [PI_NO_FILE_MATCH     , "no files match pattern"],
   [PI_NO_FILE_ACCESS    , "no permission to access file"],
   [PI_FILE_IS_A_DIR     , "file is a directory"],
   [PI_BAD_SHELL_STATUS  , "bad shell return status"],
   [PI_BAD_SCRIPT_NAME   , "bad script name"],
   [PI_BAD_SPI_BAUD      , "bad SPI baud rate, not 50-500k"],
   [PI_NOT_SPI_GPIO      , "no bit bang SPI in progress on GPIO"],
   [PI_BAD_EVENT_ID      , "bad event id"],
]

_except_a = "%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n{}"

_except_z = "%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%"

_except_1 = """
Did you start the pigpio daemon? E.g. sudo pigpiod

Did you specify the correct Pi host/port in the environment
variables PIGPIO_ADDR/PIGPIO_PORT?
E.g. export PIGPIO_ADDR=soft, export PIGPIO_PORT=8888

Did you specify the correct Pi host/port in the
pigpio.pi() function? E.g. pigpio.pi('soft', 8888)"""

_except_2 = """
Do you have permission to access the pigpio daemon?
Perhaps it was started with sudo pigpiod -nlocalhost"""

_except_3 = """
Can't create callback thread.
Perhaps too many simultaneous pigpio connections."""

class _socklock:
   """
   A class to store socket and lock.
   """
   def __init__(self):
      self.s = None
      self.l = threading.RLock()

class error(Exception):
   """pigpio module exception"""
   def __init__(self, value):
      self.value = value
   def __str__(self):
      return repr(self.value)

class pulse:
   """
   A class to store pulse information.
   """

   def __init__(self, gpio_on, gpio_off, delay):
      """
      Initialises a pulse.

       gpio_on:= the GPIO to switch on at the start of the pulse.
      gpio_off:= the GPIO to switch off at the start of the pulse.
         delay:= the delay in microseconds before the next pulse.

      """
      self.gpio_on = gpio_on
      self.gpio_off = gpio_off
      self.delay = delay

def error_text(errnum):
   """
   Returns a text description of a pigpio error.

   errnum:= <0, the error number

   ...
   print(pigpio.error_text(-5))
   level not 0-1
   ...
   """
   for e in _errors:
      if e[0] == errnum:
         return e[1]
   return "unknown error ({})".format(errnum)

def tickDiff(t1, t2):
   """
   Returns the microsecond difference between two ticks.

   t1:= the earlier tick
   t2:= the later tick

   ...
   print(pigpio.tickDiff(4294967272, 12))
   36
   ...
   """
   tDiff = t2 - t1
   if tDiff < 0:
      tDiff += (1 << 32)
   return tDiff

# A couple of hacks to cope with different string handling
# between various Python versions
# 3 != 2.7.8 != 2.7.3

if sys.hexversion < 0x03000000:
   def _b(x):
      return x
else:
   def _b(x):
      return x.encode('latin-1')

if sys.hexversion < 0x02070800:
   def _str(x):
      return buffer(x)
else:
   def _str(x):
      return x

def u2i(uint32):
   """
   Converts a 32 bit unsigned number to signed.

   uint32:= an unsigned 32 bit number

   ...
   print(u2i(4294967272))
   -24
   print(u2i(37))
   37
   ...
   """
   mask = (2 ** 32) - 1
   if uint32 & (1 << 31):
      v = uint32 | ~mask
   else:
      v = uint32 & mask
   return v

def _u2i(uint32):
   """
   Converts a 32 bit unsigned number to signed.  If the number
   is negative it indicates an error.  On error a pigpio
   exception will be raised if exceptions is True.
   """
   v = u2i(uint32)
   if v < 0:
      if exceptions:
         raise error(error_text(v))
   return v

def _pigpio_command(sl, cmd, p1, p2):
   """
   Runs a pigpio socket command.

    sl:= command socket and lock.
   cmd:= the command to be executed.
    p1:= command parameter 1 (if applicable).
    p2:= command parameter 2 (if applicable).
   """
   sl.l.acquire()
   try:
      sl.s.send(struct.pack('IIII', cmd, p1, p2, 0))
      dummy, res = struct.unpack('12sI', sl.s.recv(_SOCK_CMD_LEN))
   finally:
      sl.l.release()
   return res

def _pigpio_command_ext(sl, cmd, p1, p2, p3, extents):
   """
   Runs an extended pigpio socket command.

        sl:= command socket and lock.
       cmd:= the command to be executed.
        p1:= command parameter 1 (if applicable).
        p2:= command parameter 2 (if applicable).
        p3:= total size in bytes of following extents
   extents:= additional data blocks
   """
   ext = bytearray(struct.pack('IIII', cmd, p1, p2, p3))
   for x in extents:
      if type(x) == type(""):
         ext.extend(_b(x))
      else:
         ext.extend(x)
   sl.l.acquire()
   try:
      sl.s.sendall(ext)
      dummy, res = struct.unpack('12sI', sl.s.recv(_SOCK_CMD_LEN))
   finally:
      sl.l.release()
   return res

class _event_ADT:
   """
   An ADT class to hold event callback information.
   """

   def __init__(self, event, func):
      """
      Initialises an event callback ADT.

      event:= the event id.
       func:= a user function taking one argument, the event id.
      """
      self.event = event
      self.func = func
      self.bit = 1<<event

class _callback_ADT:
   """An ADT class to hold callback information."""

   def __init__(self, gpio, edge, func):
      """
      Initialises a callback ADT.

      gpio:= Broadcom GPIO number.
      edge:= EITHER_EDGE, RISING_EDGE, or FALLING_EDGE.
      func:= a user function taking three arguments (GPIO, level, tick).
      """
      self.gpio = gpio
      self.edge = edge
      self.func = func
      self.bit = 1<<gpio

class _callback_thread(threading.Thread):
   """A class to encapsulate pigpio notification callbacks."""
   def __init__(self, control, host, port):
      """Initialises notifications."""
      threading.Thread.__init__(self)
      self.control = control
      self.sl = _socklock()
      self.go = False
      self.daemon = True
      self.monitor = 0
      self.event_bits = 0
      self.callbacks = []
      self.events = []
      self.sl.s = socket.create_connection((host, port), None)
      self.lastLevel = _pigpio_command(self.sl,  _PI_CMD_BR1, 0, 0)
      self.handle = _u2i(_pigpio_command(self.sl, _PI_CMD_NOIB, 0, 0))
      self.go = True
      self.start()

   def stop(self):
      """Stops notifications."""
      if self.go:
         self.go = False
         self.sl.s.send(struct.pack('IIII', _PI_CMD_NC, self.handle, 0, 0))

   def append(self, callb):
      """Adds a callback to the notification thread."""
      self.callbacks.append(callb)
      self.monitor = self.monitor | callb.bit
      _pigpio_command(self.control, _PI_CMD_NB, self.handle, self.monitor)

   def remove(self, callb):
      """Removes a callback from the notification thread."""
      if callb in self.callbacks:
         self.callbacks.remove(callb)
         newMonitor = 0
         for c in self.callbacks:
            newMonitor |= c.bit
         if newMonitor != self.monitor:
            self.monitor = newMonitor
            _pigpio_command(
               self.control, _PI_CMD_NB, self.handle, self.monitor)

   def append_event(self, callb):
      """
      Adds an event callback to the notification thread.
      """
      self.events.append(callb)
      self.event_bits = self.event_bits | callb.bit
      _pigpio_command(self.control, _PI_CMD_EVM, self.handle, self.event_bits)

   def remove_event(self, callb):
      """
      Removes an event callback from the notification thread.
      """
      if callb in self.events:
         self.events.remove(callb)
         new_event_bits = 0
         for c in self.events:
            new_event_bits |= c.bit
         if new_event_bits != self.event_bits:
            self.event_bits = new_event_bits
            _pigpio_command(
               self.control, _PI_CMD_EVM, self.handle, self.event_bits)

   def run(self):
      """Runs the notification thread."""

      lastLevel = self.lastLevel

      RECV_SIZ = 4096
      MSG_SIZ = 12

      buf = bytes()
      while self.go:

         buf += self.sl.s.recv(RECV_SIZ)
         offset = 0

         while self.go and (len(buf) - offset) >= MSG_SIZ:
            msgbuf = buf[offset:offset + MSG_SIZ]
            offset += MSG_SIZ
            seq, flags, tick, level = (struct.unpack('HHII', msgbuf))

            if flags == 0:
               changed = level ^ lastLevel
               lastLevel = level
               for cb in self.callbacks:
                  if cb.bit & changed:
                     newLevel = 0
                     if cb.bit & level:
                        newLevel = 1
                     if (cb.edge ^ newLevel):
                         cb.func(cb.gpio, newLevel, tick)
            else:
               if flags & NTFY_FLAGS_WDOG:
                  gpio = flags & NTFY_FLAGS_GPIO
                  for cb in self.callbacks:
                     if cb.gpio == gpio:
                        cb.func(gpio, TIMEOUT, tick)
               elif flags & NTFY_FLAGS_EVENT:
                  event = flags & NTFY_FLAGS_GPIO
                  for cb in self.events:
                     if cb.event == event:
                        cb.func(event, tick)
         buf = buf[offset:]

      self.sl.s.close()

class _callback:
   """A class to provide GPIO level change callbacks."""

   def __init__(self, notify, user_gpio, edge=RISING_EDGE, func=None):
      """
      Initialise a callback and adds it to the notification thread.
      """
      self._notify = notify
      self.count=0
      self._reset = False
      if func is None:
         func=self._tally
      self.callb = _callback_ADT(user_gpio, edge, func)
      self._notify.append(self.callb)

   def cancel(self):
      """Cancels a callback by removing it from the notification thread."""
      self._notify.remove(self.callb)

   def _tally(self, user_gpio, level, tick):
      """Increment the callback called count."""
      if self._reset:
         self._reset = False
         self.count = 0
      self.count += 1

   def tally(self):
      """
      Provides a count of how many times the default tally
      callback has triggered.

      The count will be zero if the user has supplied their own
      callback function.
      """
      return self.count

   def reset_tally(self):
      """
      Resets the tally count to zero.
      """
      self._reset = True
      self.count = 0

class _event:
   """A class to provide event callbacks."""

   def __init__(self, notify, event, func=None):
      """
      Initialise an event and adds it to the notification thread.
      """
      self._notify = notify
      self.count=0
      self._reset = False
      if func is None:
         func=self._tally
      self.callb = _event_ADT(event, func)
      self._notify.append_event(self.callb)

   def cancel(self):
      """
      Cancels a event callback by removing it from the
      notification thread.
      """
      self._notify.remove_event(self.callb)

   def _tally(self, event, tick):
      """Increment the event callback called count."""
      if self._reset:
         self._reset = False
         self.count = 0
      self.count += 1

   def tally(self):
      """
      Provides a count of how many times the default tally
      callback has triggered.

      The count will be zero if the user has supplied their own
      callback function.
      """
      return self.count

   def reset_tally(self):
      """
      Resets the tally count to zero.
      """
      self._reset = True
      self.count = 0

class _wait_for_edge:
   """Encapsulates waiting for GPIO edges."""

   def __init__(self, notify, gpio, edge, timeout):
      """Initialises a wait_for_edge."""
      self._notify = notify
      self.callb = _callback_ADT(gpio, edge, self.func)
      self.trigger = False
      self._notify.append(self.callb)
      self.start = time.time()
      while (self.trigger == False) and ((time.time()-self.start) < timeout):
         time.sleep(0.05)
      self._notify.remove(self.callb)

   def func(self, gpio, level, tick):
      """Sets wait_for_edge triggered."""
      self.trigger = True

class _wait_for_event:
   """Encapsulates waiting for an event."""

   def __init__(self, notify, event, timeout):
      """Initialises wait_for_event."""
      self._notify = notify
      self.callb = _event_ADT(event, self.func)
      self.trigger = False
      self._notify.append_event(self.callb)
      self.start = time.time()
      while (self.trigger == False) and ((time.time()-self.start) < timeout):
         time.sleep(0.05)
      self._notify.remove_event(self.callb)

   def func(self, event, tick):
      """Sets wait_for_event triggered."""
      self.trigger = True

class pi():

   def _rxbuf(self, count):
      """Returns count bytes from the command socket."""
      ext = bytearray(self.sl.s.recv(count))
      while len(ext) < count:
         ext.extend(self.sl.s.recv(count - len(ext)))
      return ext

   def set_mode(self, gpio, mode):
      """
      Sets the GPIO mode.

      gpio:= 0-53.
      mode:= INPUT, OUTPUT, ALT0, ALT1, ALT2, ALT3, ALT4, ALT5.

      ...
      pi.set_mode( 4, pigpio.INPUT)  # GPIO  4 as input
      pi.set_mode(17, pigpio.OUTPUT) # GPIO 17 as output
      pi.set_mode(24, pigpio.ALT2)   # GPIO 24 as ALT2
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_MODES, gpio, mode))

   def get_mode(self, gpio):
      """
      Returns the GPIO mode.

      gpio:= 0-53.

      Returns a value as follows

      . .
      0 = INPUT
      1 = OUTPUT
      2 = ALT5
      3 = ALT4
      4 = ALT0
      5 = ALT1
      6 = ALT2
      7 = ALT3
      . .

      ...
      print(pi.get_mode(0))
      4
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_MODEG, gpio, 0))

   def set_pull_up_down(self, gpio, pud):
      """
      Sets or clears the internal GPIO pull-up/down resistor.

      gpio:= 0-53.
       pud:= PUD_UP, PUD_DOWN, PUD_OFF.

      ...
      pi.set_pull_up_down(17, pigpio.PUD_OFF)
      pi.set_pull_up_down(23, pigpio.PUD_UP)
      pi.set_pull_up_down(24, pigpio.PUD_DOWN)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PUD, gpio, pud))

   def read(self, gpio):
      """
      Returns the GPIO level.

      gpio:= 0-53.

      ...
      pi.set_mode(23, pigpio.INPUT)

      pi.set_pull_up_down(23, pigpio.PUD_DOWN)
      print(pi.read(23))
      0

      pi.set_pull_up_down(23, pigpio.PUD_UP)
      print(pi.read(23))
      1
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_READ, gpio, 0))

   def write(self, gpio, level):
      """
      Sets the GPIO level.

       GPIO:= 0-53.
      level:= 0, 1.

      If PWM or servo pulses are active on the GPIO they are
      switched off.

      ...
      pi.set_mode(17, pigpio.OUTPUT)

      pi.write(17,0)
      print(pi.read(17))
      0

      pi.write(17,1)
      print(pi.read(17))
      1
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WRITE, gpio, level))

   def set_PWM_dutycycle(self, user_gpio, dutycycle):
      """
      Starts (non-zero dutycycle) or stops (0) PWM pulses on the GPIO.

      user_gpio:= 0-31.
      dutycycle:= 0-range (range defaults to 255).

      The [*set_PWM_range*] function can change the default range of 255.

      ...
      pi.set_PWM_dutycycle(4,   0) # PWM off
      pi.set_PWM_dutycycle(4,  64) # PWM 1/4 on
      pi.set_PWM_dutycycle(4, 128) # PWM 1/2 on
      pi.set_PWM_dutycycle(4, 192) # PWM 3/4 on
      pi.set_PWM_dutycycle(4, 255) # PWM full on
      ...
      """
      return _u2i(_pigpio_command(
         self.sl, _PI_CMD_PWM, user_gpio, int(dutycycle)))

   def get_PWM_dutycycle(self, user_gpio):
      """
      Returns the PWM dutycycle being used on the GPIO.

      user_gpio:= 0-31.

      Returns the PWM dutycycle.


      For normal PWM the dutycycle will be out of the defined range
      for the GPIO (see [*get_PWM_range*]).

      If a hardware clock is active on the GPIO the reported
      dutycycle will be 500000 (500k) out of 1000000 (1M).

      If hardware PWM is active on the GPIO the reported dutycycle
      will be out of a 1000000 (1M).

      ...
      pi.set_PWM_dutycycle(4, 25)
      print(pi.get_PWM_dutycycle(4))
      25

      pi.set_PWM_dutycycle(4, 203)
      print(pi.get_PWM_dutycycle(4))
      203
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_GDC, user_gpio, 0))

   def set_PWM_range(self, user_gpio, range_):
      """
      Sets the range of PWM values to be used on the GPIO.

      user_gpio:= 0-31.
         range_:= 25-40000.

      ...
      pi.set_PWM_range(9, 100)  # now  25 1/4,   50 1/2,   75 3/4 on
      pi.set_PWM_range(9, 500)  # now 125 1/4,  250 1/2,  375 3/4 on
      pi.set_PWM_range(9, 3000) # now 750 1/4, 1500 1/2, 2250 3/4 on
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PRS, user_gpio, range_))

   def get_PWM_range(self, user_gpio):
      """
      Returns the range of PWM values being used on the GPIO.

      user_gpio:= 0-31.

      If a hardware clock or hardware PWM is active on the GPIO
      the reported range will be 1000000 (1M).

      ...
      pi.set_PWM_range(9, 500)
      print(pi.get_PWM_range(9))
      500
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PRG, user_gpio, 0))

   def get_PWM_real_range(self, user_gpio):
      """
      Returns the real (underlying) range of PWM values being
      used on the GPIO.

      user_gpio:= 0-31.

      If a hardware clock is active on the GPIO the reported
      real range will be 1000000 (1M).

      If hardware PWM is active on the GPIO the reported real range
      will be approximately 250M divided by the set PWM frequency.

      ...
      pi.set_PWM_frequency(4, 800)
      print(pi.get_PWM_real_range(4))
      250
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PRRG, user_gpio, 0))

   def set_PWM_frequency(self, user_gpio, frequency):
      """
      Sets the frequency (in Hz) of the PWM to be used on the GPIO.

      user_gpio:= 0-31.
      frequency:= >=0 Hz

      Returns the numerically closest frequency if OK, otherwise
      PI_BAD_USER_GPIO or PI_NOT_PERMITTED.

      If PWM is currently active on the GPIO it will be switched
      off and then back on at the new frequency.

      Each GPIO can be independently set to one of 18 different
      PWM frequencies.

      The selectable frequencies depend upon the sample rate which
      may be 1, 2, 4, 5, 8, or 10 microseconds (default 5).  The
      sample rate is set when the pigpio daemon is started.

      The frequencies for each sample rate are:

      . .
                             Hertz

             1: 40000 20000 10000 8000 5000 4000 2500 2000 1600
                 1250  1000   800  500  400  250  200  100   50

             2: 20000 10000  5000 4000 2500 2000 1250 1000  800
                  625   500   400  250  200  125  100   50   25

             4: 10000  5000  2500 2000 1250 1000  625  500  400
                  313   250   200  125  100   63   50   25   13
      sample
       rate
       (us)  5:  8000  4000  2000 1600 1000  800  500  400  320
                  250   200   160  100   80   50   40   20   10

             8:  5000  2500  1250 1000  625  500  313  250  200
                  156   125   100   63   50   31   25   13    6

            10:  4000  2000  1000  800  500  400  250  200  160
                  125   100    80   50   40   25   20   10    5
      . .

      ...
      pi.set_PWM_frequency(4,0)
      print(pi.get_PWM_frequency(4))
      10

      pi.set_PWM_frequency(4,100000)
      print(pi.get_PWM_frequency(4))
      8000
      ...
      """
      return _u2i(
         _pigpio_command(self.sl, _PI_CMD_PFS, user_gpio, frequency))

   def get_PWM_frequency(self, user_gpio):
      """
      Returns the frequency of PWM being used on the GPIO.

      user_gpio:= 0-31.

      Returns the frequency (in Hz) used for the GPIO.

      For normal PWM the frequency will be that defined for the GPIO
      by [*set_PWM_frequency*].

      If a hardware clock is active on the GPIO the reported frequency
      will be that set by [*hardware_clock*].

      If hardware PWM is active on the GPIO the reported frequency
      will be that set by [*hardware_PWM*].

      ...
      pi.set_PWM_frequency(4,0)
      print(pi.get_PWM_frequency(4))
      10

      pi.set_PWM_frequency(4, 800)
      print(pi.get_PWM_frequency(4))
      800
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PFG, user_gpio, 0))

   def set_servo_pulsewidth(self, user_gpio, pulsewidth):
      """
      Starts (500-2500) or stops (0) servo pulses on the GPIO.

       user_gpio:= 0-31.
      pulsewidth:= 0 (off),
                   500 (most anti-clockwise) - 2500 (most clockwise).

      The selected pulsewidth will continue to be transmitted until
      changed by a subsequent call to set_servo_pulsewidth.

      The pulsewidths supported by servos varies and should probably
      be determined by experiment. A value of 1500 should always be
      safe and represents the mid-point of rotation.

      You can DAMAGE a servo if you command it to move beyond its
      limits.

      ...
      pi.set_servo_pulsewidth(17, 0)    # off
      pi.set_servo_pulsewidth(17, 1000) # safe anti-clockwise
      pi.set_servo_pulsewidth(17, 1500) # centre
      pi.set_servo_pulsewidth(17, 2000) # safe clockwise
      ...
   """
      return _u2i(_pigpio_command(
         self.sl, _PI_CMD_SERVO, user_gpio, int(pulsewidth)))

   def get_servo_pulsewidth(self, user_gpio):
      """
      Returns the servo pulsewidth being used on the GPIO.

      user_gpio:= 0-31.

      Returns the servo pulsewidth.

      ...
      pi.set_servo_pulsewidth(4, 525)
      print(pi.get_servo_pulsewidth(4))
      525

      pi.set_servo_pulsewidth(4, 2130)
      print(pi.get_servo_pulsewidth(4))
      2130
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_GPW, user_gpio, 0))

   def notify_open(self):
      """
      Returns a notification handle (>=0).

      A notification is a method for being notified of GPIO state
      changes via a pipe.

      Pipes are only accessible from the local machine so this
      function serves no purpose if you are using Python from a
      remote machine.  The in-built (socket) notifications
      provided by [*callback*] should be used instead.

      Notifications for handle x will be available at the pipe
      named /dev/pigpiox (where x is the handle number).

      E.g. if the function returns 15 then the notifications must be
      read from /dev/pigpio15.

      Notifications have the following structure:

      . .
      H seqno
      H flags
      I tick
      I level
      . .

      seqno: starts at 0 each time the handle is opened and then
      increments by one for each report.

      flags: three flags are defined, PI_NTFY_FLAGS_WDOG,
      PI_NTFY_FLAGS_ALIVE, and PI_NTFY_FLAGS_EVENT.

      If bit 5 is set (PI_NTFY_FLAGS_WDOG) then bits 0-4 of the
      flags indicate a GPIO which has had a watchdog timeout.

      If bit 6 is set (PI_NTFY_FLAGS_ALIVE) this indicates a keep
      alive signal on the pipe/socket and is sent once a minute
      in the absence of other notification activity.

      If bit 7 is set (PI_NTFY_FLAGS_EVENT) then bits 0-4 of the
      flags indicate an event which has been triggered.


      tick: the number of microseconds since system boot.  It wraps
      around after 1h12m.

      level: indicates the level of each GPIO.  If bit 1<<x is set
      then GPIO x is high.

      ...
      h = pi.notify_open()
      if h >= 0:
         pi.notify_begin(h, 1234)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_NO, 0, 0))

   def notify_begin(self, handle, bits):
      """
      Starts notifications on a handle.

      handle:= >=0 (as returned by a prior call to [*notify_open*])
        bits:= a 32 bit mask indicating the GPIO to be notified.

      The notification sends state changes for each GPIO whose
      corresponding bit in bits is set.

      The following code starts notifications for GPIO 1, 4,
      6, 7, and 10 (1234 = 0x04D2 = 0b0000010011010010).

      ...
      h = pi.notify_open()
      if h >= 0:
         pi.notify_begin(h, 1234)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_NB, handle, bits))

   def notify_pause(self, handle):
      """
      Pauses notifications on a handle.

      handle:= >=0 (as returned by a prior call to [*notify_open*])

      Notifications for the handle are suspended until
      [*notify_begin*] is called again.

      ...
      h = pi.notify_open()
      if h >= 0:
         pi.notify_begin(h, 1234)
         ...
         pi.notify_pause(h)
         ...
         pi.notify_begin(h, 1234)
         ...
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_NB, handle, 0))

   def notify_close(self, handle):
      """
      Stops notifications on a handle and releases the handle for reuse.

      handle:= >=0 (as returned by a prior call to [*notify_open*])

      ...
      h = pi.notify_open()
      if h >= 0:
         pi.notify_begin(h, 1234)
         ...
         pi.notify_close(h)
         ...
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_NC, handle, 0))

   def set_watchdog(self, user_gpio, wdog_timeout):
      """
      Sets a watchdog timeout for a GPIO.

         user_gpio:= 0-31.
      wdog_timeout:= 0-60000.

      The watchdog is nominally in milliseconds.

      Only one watchdog may be registered per GPIO.

      The watchdog may be cancelled by setting timeout to 0.

      Once a watchdog has been started callbacks for the GPIO
      will be triggered every timeout interval after the last
      GPIO activity.

      The callback will receive the special level TIMEOUT.

      ...
      pi.set_watchdog(23, 1000) # 1000 ms watchdog on GPIO 23
      pi.set_watchdog(23, 0)    # cancel watchdog on GPIO 23
      ...
      """
      return _u2i(_pigpio_command(
         self.sl, _PI_CMD_WDOG, user_gpio, int(wdog_timeout)))

   def read_bank_1(self):
      """
      Returns the levels of the bank 1 GPIO (GPIO 0-31).

      The returned 32 bit integer has a bit set if the corresponding
      GPIO is high.  GPIO n has bit value (1<<n).

      ...
      print(bin(pi.read_bank_1()))
      0b10010100000011100100001001111
      ...
      """
      return _pigpio_command(self.sl, _PI_CMD_BR1, 0, 0)

   def read_bank_2(self):
      """
      Returns the levels of the bank 2 GPIO (GPIO 32-53).

      The returned 32 bit integer has a bit set if the corresponding
      GPIO is high.  GPIO n has bit value (1<<(n-32)).

      ...
      print(bin(pi.read_bank_2()))
      0b1111110000000000000000
      ...
      """
      return _pigpio_command(self.sl, _PI_CMD_BR2, 0, 0)

   def clear_bank_1(self, bits):
      """
      Clears GPIO 0-31 if the corresponding bit in bits is set.

      bits:= a 32 bit mask with 1 set if the corresponding GPIO is
             to be cleared.

      A returned status of PI_SOME_PERMITTED indicates that the user
      is not allowed to write to one or more of the GPIO.

      ...
      pi.clear_bank_1(int("111110010000",2))
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_BC1, bits, 0))

   def clear_bank_2(self, bits):
      """
      Clears GPIO 32-53 if the corresponding bit (0-21) in bits is set.

      bits:= a 32 bit mask with 1 set if the corresponding GPIO is
             to be cleared.

      A returned status of PI_SOME_PERMITTED indicates that the user
      is not allowed to write to one or more of the GPIO.

      ...
      pi.clear_bank_2(0x1010)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_BC2, bits, 0))

   def set_bank_1(self, bits):
      """
      Sets GPIO 0-31 if the corresponding bit in bits is set.

      bits:= a 32 bit mask with 1 set if the corresponding GPIO is
             to be set.

      A returned status of PI_SOME_PERMITTED indicates that the user
      is not allowed to write to one or more of the GPIO.

      ...
      pi.set_bank_1(int("111110010000",2))
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_BS1, bits, 0))

   def set_bank_2(self, bits):
      """
      Sets GPIO 32-53 if the corresponding bit (0-21) in bits is set.

      bits:= a 32 bit mask with 1 set if the corresponding GPIO is
             to be set.

      A returned status of PI_SOME_PERMITTED indicates that the user
      is not allowed to write to one or more of the GPIO.

      ...
      pi.set_bank_2(0x303)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_BS2, bits, 0))

   def hardware_clock(self, gpio, clkfreq):
      """
      Starts a hardware clock on a GPIO at the specified frequency.
      Frequencies above 30MHz are unlikely to work.

         gpio:= see description
      clkfreq:= 0 (off) or 4689-250000000 (250M)


      Returns 0 if OK, otherwise PI_NOT_PERMITTED, PI_BAD_GPIO,
      PI_NOT_HCLK_GPIO, PI_BAD_HCLK_FREQ,or PI_BAD_HCLK_PASS.

      The same clock is available on multiple GPIO.  The latest
      frequency setting will be used by all GPIO which share a clock.

      The GPIO must be one of the following:

      . .
      4   clock 0  All models
      5   clock 1  All models but A and B (reserved for system use)
      6   clock 2  All models but A and B
      20  clock 0  All models but A and B
      21  clock 1  All models but A and Rev.2 B (reserved for system use)

      32  clock 0  Compute module only
      34  clock 0  Compute module only
      42  clock 1  Compute module only (reserved for system use)
      43  clock 2  Compute module only
      44  clock 1  Compute module only (reserved for system use)
      . .

      Access to clock 1 is protected by a password as its use will
      likely crash the Pi.  The password is given by or'ing 0x5A000000
      with the GPIO number.

      ...
      pi.hardware_clock(4, 5000) # 5 KHz clock on GPIO 4

      pi.hardware_clock(4, 40000000) # 40 MHz clock on GPIO 4
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_HC, gpio, clkfreq))

   def hardware_PWM(self, gpio, PWMfreq, PWMduty):
      """
      Starts hardware PWM on a GPIO at the specified frequency
      and dutycycle. Frequencies above 30MHz are unlikely to work.

      NOTE: Any waveform started by [*wave_send_once*],
      [*wave_send_repeat*], or [*wave_chain*] will be cancelled.

      This function is only valid if the pigpio main clock is PCM.
      The main clock defaults to PCM but may be overridden when the
      pigpio daemon is started (option -t).

         gpio:= see descripton
      PWMfreq:= 0 (off) or 1-125000000 (125M).
      PWMduty:= 0 (off) to 1000000 (1M)(fully on).

      Returns 0 if OK, otherwise PI_NOT_PERMITTED, PI_BAD_GPIO,
      PI_NOT_HPWM_GPIO, PI_BAD_HPWM_DUTY, PI_BAD_HPWM_FREQ.

      The same PWM channel is available on multiple GPIO.
      The latest frequency and dutycycle setting will be used
      by all GPIO which share a PWM channel.

      The GPIO must be one of the following:

      . .
      12  PWM channel 0  All models but A and B
      13  PWM channel 1  All models but A and B
      18  PWM channel 0  All models
      19  PWM channel 1  All models but A and B

      40  PWM channel 0  Compute module only
      41  PWM channel 1  Compute module only
      45  PWM channel 1  Compute module only
      52  PWM channel 0  Compute module only
      53  PWM channel 1  Compute module only
      . .

      The actual number of steps beween off and fully on is the
      integral part of 250 million divided by PWMfreq.

      The actual frequency set is 250 million / steps.

      There will only be a million steps for a PWMfreq of 250.
      Lower frequencies will have more steps and higher
      frequencies will have fewer steps.  PWMduty is
      automatically scaled to take this into account.

      ...
      pi.hardware_PWM(18, 800, 250000) # 800Hz 25% dutycycle

      pi.hardware_PWM(18, 2000, 750000) # 2000Hz 75% dutycycle
      ...
      """
      # pigpio message format

      # I p1 gpio
      # I p2 PWMfreq
      # I p3 4
      ## extension ##
      # I PWMdutycycle
      extents = [struct.pack("I", PWMduty)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_HP, gpio, PWMfreq, 4, extents))


   def get_current_tick(self):
      """
      Returns the current system tick.

      Tick is the number of microseconds since system boot.  As an
      unsigned 32 bit quantity tick wraps around approximately
      every 71.6 minutes.

      ...
      t1 = pi.get_current_tick()
      time.sleep(1)
      t2 = pi.get_current_tick()
      ...
      """
      return _pigpio_command(self.sl, _PI_CMD_TICK, 0, 0)

   def get_hardware_revision(self):
      """
      Returns the Pi's hardware revision number.

      The hardware revision is the last few characters on the
      Revision line of /proc/cpuinfo.

      The revision number can be used to determine the assignment
      of GPIO to pins (see [*gpio*]).

      There are at least three types of board.

      Type 1 boards have hardware revision numbers of 2 and 3.

      Type 2 boards have hardware revision numbers of 4, 5, 6, and 15.

      Type 3 boards have hardware revision numbers of 16 or greater.

      If the hardware revision can not be found or is not a valid
      hexadecimal number the function returns 0.

      ...
      print(pi.get_hardware_revision())
      2
      ...
      """
      return _pigpio_command(self.sl, _PI_CMD_HWVER, 0, 0)

   def get_pigpio_version(self):
      """
      Returns the pigpio software version.

      ...
      v = pi.get_pigpio_version()
      ...
      """
      return _pigpio_command(self.sl, _PI_CMD_PIGPV, 0, 0)

   def wave_clear(self):
      """
      Clears all waveforms and any data added by calls to the
      [*wave_add_**] functions.

      ...
      pi.wave_clear()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVCLR, 0, 0))

   def wave_add_new(self):
      """
      Starts a new empty waveform.

      You would not normally need to call this function as it is
      automatically called after a waveform is created with the
      [*wave_create*] function.

      ...
      pi.wave_add_new()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVNEW, 0, 0))

   def wave_add_generic(self, pulses):
      """
      Adds a list of pulses to the current waveform.

      pulses:= list of pulses to add to the waveform.

      Returns the new total number of pulses in the current waveform.

      The pulses are interleaved in time order within the existing
      waveform (if any).

      Merging allows the waveform to be built in parts, that is the
      settings for GPIO#1 can be added, and then GPIO#2 etc.

      If the added waveform is intended to start after or within
      the existing waveform then the first pulse should consist
      solely of a delay.

      ...
      G1=4
      G2=24

      pi.set_mode(G1, pigpio.OUTPUT)
      pi.set_mode(G2, pigpio.OUTPUT)

      flash_500=[] # flash every 500 ms
      flash_100=[] # flash every 100 ms

      #                              ON     OFF  DELAY

      flash_500.append(pigpio.pulse(1<<G1, 1<<G2, 500000))
      flash_500.append(pigpio.pulse(1<<G2, 1<<G1, 500000))

      flash_100.append(pigpio.pulse(1<<G1, 1<<G2, 100000))
      flash_100.append(pigpio.pulse(1<<G2, 1<<G1, 100000))

      pi.wave_clear() # clear any existing waveforms

      pi.wave_add_generic(flash_500) # 500 ms flashes
      f500 = pi.wave_create() # create and save id

      pi.wave_add_generic(flash_100) # 100 ms flashes
      f100 = pi.wave_create() # create and save id

      pi.wave_send_repeat(f500)

      time.sleep(4)

      pi.wave_send_repeat(f100)

      time.sleep(4)

      pi.wave_send_repeat(f500)

      time.sleep(4)

      pi.wave_tx_stop() # stop waveform

      pi.wave_clear() # clear all waveforms
      ...
      """
      # pigpio message format

      # I p1 0
      # I p2 0
      # I p3 pulses * 12
      ## extension ##
      # III on/off/delay * pulses
      if len(pulses):
         ext = bytearray()
         for p in pulses:
            ext.extend(struct.pack("III", p.gpio_on, p.gpio_off, p.delay))
         extents = [ext]
         return _u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_WVAG, 0, 0, len(pulses)*12, extents))
      else:
         return 0

   def wave_add_serial(
      self, user_gpio, baud, data, offset=0, bb_bits=8, bb_stop=2):
      """
      Adds a waveform representing serial data to the existing
      waveform (if any).  The serial data starts [*offset*]
      microseconds from the start of the waveform.

      user_gpio:= GPIO to transmit data.  You must set the GPIO mode
                  to output.
           baud:= 50-1000000 bits per second.
           data:= the bytes to write.
         offset:= number of microseconds from the start of the
                  waveform, default 0.
        bb_bits:= number of data bits, default 8.
        bb_stop:= number of stop half bits, default 2.

      Returns the new total number of pulses in the current waveform.

      The serial data is formatted as one start bit, [*bb_bits*]
      data bits, and [*bb_stop*]/2 stop bits.

      It is legal to add serial data streams with different baud
      rates to the same waveform.

      The bytes required for each character depend upon [*bb_bits*].

      For [*bb_bits*] 1-8 there will be one byte per character. 
      For [*bb_bits*] 9-16 there will be two bytes per character. 
      For [*bb_bits*] 17-32 there will be four bytes per character.

      ...
      pi.wave_add_serial(4, 300, 'Hello world')

      pi.wave_add_serial(4, 300, b"Hello world")

      pi.wave_add_serial(4, 300, b'\\x23\\x01\\x00\\x45')

      pi.wave_add_serial(17, 38400, [23, 128, 234], 5000)
      ...
      """
      # pigpio message format

      # I p1 gpio
      # I p2 baud
      # I p3 len+12
      ## extension ##
      # I bb_bits
      # I bb_stop
      # I offset
      # s len data bytes
      if len(data):
         extents = [struct.pack("III", bb_bits, bb_stop, offset), data]
         return _u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_WVAS, user_gpio, baud, len(data)+12, extents))
      else:
         return 0

   def wave_create(self):
      """
      Creates a waveform from the data provided by the prior calls
      to the [*wave_add_**] functions.

      Returns a wave id (>=0) if OK,  otherwise PI_EMPTY_WAVEFORM,
      PI_TOO_MANY_CBS, PI_TOO_MANY_OOL, or PI_NO_WAVEFORM_ID.

      The data provided by the [*wave_add_**] functions is consumed by
      this function.

      As many waveforms may be created as there is space available.
      The wave id is passed to [*wave_send_**] to specify the waveform
      to transmit.

      Normal usage would be

      Step 1. [*wave_clear*] to clear all waveforms and added data.

      Step 2. [*wave_add_**] calls to supply the waveform data.

      Step 3. [*wave_create*] to create the waveform and get a unique id

      Repeat steps 2 and 3 as needed.

      Step 4. [*wave_send_**] with the id of the waveform to transmit.

      A waveform comprises one or more pulses.

      A pulse specifies

      1) the GPIO to be switched on at the start of the pulse. 
      2) the GPIO to be switched off at the start of the pulse. 
      3) the delay in microseconds before the next pulse.

      Any or all the fields can be zero.  It doesn't make any sense
      to set all the fields to zero (the pulse will be ignored).

      When a waveform is started each pulse is executed in order with
      the specified delay between the pulse and the next.

      ...
      wid = pi.wave_create()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVCRE, 0, 0))

   def wave_delete(self, wave_id):
      """
      This function deletes the waveform with id wave_id.

      wave_id:= >=0 (as returned by a prior call to [*wave_create*]).

      Wave ids are allocated in order, 0, 1, 2, etc.

      ...
      pi.wave_delete(6) # delete waveform with id 6

      pi.wave_delete(0) # delete waveform with id 0
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVDEL, wave_id, 0))

   def wave_tx_start(self): # DEPRECATED
      """
      This function is deprecated and has been removed.

      Use [*wave_create*]/[*wave_send_**] instead.
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVGO, 0, 0))

   def wave_tx_repeat(self): # DEPRECATED
      """
      This function is deprecated and has beeen removed.

      Use [*wave_create*]/[*wave_send_**] instead.
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVGOR, 0, 0))

   def wave_send_once(self, wave_id):
      """
      Transmits the waveform with id wave_id.  The waveform is sent
      once.

      NOTE: Any hardware PWM started by [*hardware_PWM*] will
      be cancelled.

      wave_id:= >=0 (as returned by a prior call to [*wave_create*]).

      Returns the number of DMA control blocks used in the waveform.

      ...
      cbs = pi.wave_send_once(wid)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVTX, wave_id, 0))

   def wave_send_repeat(self, wave_id):
      """
      Transmits the waveform with id wave_id.  The waveform repeats
      until wave_tx_stop is called or another call to [*wave_send_**]
      is made.

      NOTE: Any hardware PWM started by [*hardware_PWM*] will
      be cancelled.

      wave_id:= >=0 (as returned by a prior call to [*wave_create*]).

      Returns the number of DMA control blocks used in the waveform.

      ...
      cbs = pi.wave_send_repeat(wid)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVTXR, wave_id, 0))

   def wave_send_using_mode(self, wave_id, mode):
      """
      Transmits the waveform with id wave_id using mode mode.

      wave_id:= >=0 (as returned by a prior call to [*wave_create*]).
         mode:= WAVE_MODE_ONE_SHOT, WAVE_MODE_REPEAT,
                WAVE_MODE_ONE_SHOT_SYNC, or WAVE_MODE_REPEAT_SYNC.

      WAVE_MODE_ONE_SHOT: same as [*wave_send_once*].

      WAVE_MODE_REPEAT same as [*wave_send_repeat*].

      WAVE_MODE_ONE_SHOT_SYNC same as [*wave_send_once*] but tries
      to sync with the previous waveform.

      WAVE_MODE_REPEAT_SYNC same as [*wave_send_repeat*] but tries
      to sync with the previous waveform.

      WARNING: bad things may happen if you delete the previous
      waveform before it has been synced to the new waveform.

      NOTE: Any hardware PWM started by [*hardware_PWM*] will
      be cancelled.

      wave_id:= >=0 (as returned by a prior call to [*wave_create*]).

      Returns the number of DMA control blocks used in the waveform.

      ...
      cbs = pi.wave_send_using_mode(wid, WAVE_MODE_REPEAT_SYNC)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVTXM, wave_id, mode))

   def wave_tx_at(self):
      """
      Returns the id of the waveform currently being
      transmitted.

      Returns the waveform id or one of the following special
      values:

      WAVE_NOT_FOUND (9998) - transmitted wave not found. 
      NO_TX_WAVE (9999) - no wave being transmitted.

      ...
      wid = pi.wave_tx_at()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVTAT, 0, 0))

   def wave_tx_busy(self):
      """
      Returns 1 if a waveform is currently being transmitted,
      otherwise 0.

      ...
      pi.wave_send_once(0) # send first waveform

      while pi.wave_tx_busy(): # wait for waveform to be sent
         time.sleep(0.1)

      pi.wave_send_once(1) # send next waveform
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVBSY, 0, 0))

   def wave_tx_stop(self):
      """
      Stops the transmission of the current waveform.

      This function is intended to stop a waveform started with
      wave_send_repeat.

      ...
      pi.wave_send_repeat(3)

      time.sleep(5)

      pi.wave_tx_stop()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVHLT, 0, 0))

   def wave_chain(self, data):
      """
      This function transmits a chain of waveforms.

      NOTE: Any hardware PWM started by [*hardware_PWM*]
      will be cancelled.

      The waves to be transmitted are specified by the contents
      of data which contains an ordered list of [*wave_id*]s
      and optional command codes and related data.

      Returns 0 if OK, otherwise PI_CHAIN_NESTING,
      PI_CHAIN_LOOP_CNT, PI_BAD_CHAIN_LOOP, PI_BAD_CHAIN_CMD,
      PI_CHAIN_COUNTER, PI_BAD_CHAIN_DELAY, PI_CHAIN_TOO_BIG,
      or PI_BAD_WAVE_ID.

      Each wave is transmitted in the order specified.  A wave
      may occur multiple times per chain.

      A blocks of waves may be transmitted multiple times by
      using the loop commands. The block is bracketed by loop
      start and end commands.  Loops may be nested.

      Delays between waves may be added with the delay command.

      The following command codes are supported:

      Name         @ Cmd & Data @ Meaning
      Loop Start   @ 255 0      @ Identify start of a wave block
      Loop Repeat  @ 255 1 x y  @ loop x + y*256 times
      Delay        @ 255 2 x y  @ delay x + y*256 microseconds
      Loop Forever @ 255 3      @ loop forever

      If present Loop Forever must be the last entry in the chain.

      The code is currently dimensioned to support a chain with
      roughly 600 entries and 20 loop counters.

      ...
      #!/usr/bin/env python

      import time
      import pigpio

      WAVES=5
      GPIO=4

      wid=[0]*WAVES

      pi = pigpio.pi() # Connect to local Pi.

      pi.set_mode(GPIO, pigpio.OUTPUT);

      for i in range(WAVES):
         pi.wave_add_generic([
            pigpio.pulse(1<<GPIO, 0, 20),
            pigpio.pulse(0, 1<<GPIO, (i+1)*200)]);

         wid[i] = pi.wave_create();

      pi.wave_chain([
         wid[4], wid[3], wid[2],       # transmit waves 4+3+2
         255, 0,                       # loop start
            wid[0], wid[0], wid[0],    # transmit waves 0+0+0
            255, 0,                    # loop start
               wid[0], wid[1],         # transmit waves 0+1
               255, 2, 0x88, 0x13,     # delay 5000us
            255, 1, 30, 0,             # loop end (repeat 30 times)
            255, 0,                    # loop start
               wid[2], wid[3], wid[0], # transmit waves 2+3+0
               wid[3], wid[1], wid[2], # transmit waves 3+1+2
            255, 1, 10, 0,             # loop end (repeat 10 times)
         255, 1, 5, 0,                 # loop end (repeat 5 times)
         wid[4], wid[4], wid[4],       # transmit waves 4+4+4
         255, 2, 0x20, 0x4E,           # delay 20000us
         wid[0], wid[0], wid[0],       # transmit waves 0+0+0
         ])

      while pi.wave_tx_busy():
         time.sleep(0.1);

      for i in range(WAVES):
         pi.wave_delete(wid[i])

      pi.stop()
      ...
      """
      # I p1 0
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_WVCHA, 0, 0, len(data), [data]))


   def wave_get_micros(self):
      """
      Returns the length in microseconds of the current waveform.

      ...
      micros = pi.wave_get_micros()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVSM, 0, 0))

   def wave_get_max_micros(self):
      """
      Returns the maximum possible size of a waveform in microseconds.

      ...
      micros = pi.wave_get_max_micros()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVSM, 2, 0))

   def wave_get_pulses(self):
      """
      Returns the length in pulses of the current waveform.

      ...
      pulses = pi.wave_get_pulses()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVSP, 0, 0))

   def wave_get_max_pulses(self):
      """
      Returns the maximum possible size of a waveform in pulses.

      ...
      pulses = pi.wave_get_max_pulses()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVSP, 2, 0))

   def wave_get_cbs(self):
      """
      Returns the length in DMA control blocks of the current
      waveform.

      ...
      cbs = pi.wave_get_cbs()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVSC, 0, 0))

   def wave_get_max_cbs(self):
      """
      Returns the maximum possible size of a waveform in DMA
      control blocks.

      ...
      cbs = pi.wave_get_max_cbs()
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_WVSC, 2, 0))

   def i2c_open(self, i2c_bus, i2c_address, i2c_flags=0):
      """
      Returns a handle (>=0) for the device at the I2C bus address.

          i2c_bus:= >=0.
      i2c_address:= 0-0x7F.
        i2c_flags:= 0, no flags are currently defined.

      Normally you would only use the [*i2c_**] functions if
      you are or will be connecting to the Pi over a network.  If
      you will always run on the local Pi use the standard SMBus
      module instead.

      Physically buses 0 and 1 are available on the Pi.  Higher
      numbered buses will be available if a kernel supported bus
      multiplexor is being used.

      For the SMBus commands the low level transactions are shown
      at the end of the function description.  The following
      abbreviations are used:

      . .
      S     (1 bit) : Start bit
      P     (1 bit) : Stop bit
      Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0.
      A, NA (1 bit) : Accept and not accept bit. 
      Addr  (7 bits): I2C 7 bit address.
      reg   (8 bits): Command byte, which often selects a register.
      Data  (8 bits): A data byte.
      Count (8 bits): A byte defining the length of a block operation.

      [..]: Data sent by the device.
      . .

      ...
      h = pi.i2c_open(1, 0x53) # open device at address 0x53 on bus 1
      ...
      """
      # I p1 i2c_bus
      # I p2 i2c_addr
      # I p3 4
      ## extension ##
      # I i2c_flags
      extents = [struct.pack("I", i2c_flags)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_I2CO, i2c_bus, i2c_address, 4, extents))

   def i2c_close(self, handle):
      """
      Closes the I2C device associated with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).

      ...
      pi.i2c_close(h)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_I2CC, handle, 0))

   def i2c_write_quick(self, handle, bit):
      """
      Sends a single bit to the device associated with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
         bit:= 0 or 1, the value to write.

      SMBus 2.0 5.5.1 - Quick command.
      . .
      S Addr bit [A] P
      . .

      ...
      pi.i2c_write_quick(0, 1) # send 1 to device 0
      pi.i2c_write_quick(3, 0) # send 0 to device 3
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_I2CWQ, handle, bit))

   def i2c_write_byte(self, handle, byte_val):
      """
      Sends a single byte to the device associated with handle.

        handle:= >=0 (as returned by a prior call to [*i2c_open*]).
      byte_val:= 0-255, the value to write.

      SMBus 2.0 5.5.2 - Send byte.
      . .
      S Addr Wr [A] byte_val [A] P
      . .

      ...
      pi.i2c_write_byte(1, 17)   # send byte   17 to device 1
      pi.i2c_write_byte(2, 0x23) # send byte 0x23 to device 2
      ...
      """
      return _u2i(
         _pigpio_command(self.sl, _PI_CMD_I2CWS, handle, byte_val))

   def i2c_read_byte(self, handle):
      """
      Reads a single byte from the device associated with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).

      SMBus 2.0 5.5.3 - Receive byte.
      . .
      S Addr Rd [A] [Data] NA P
      . .

      ...
      b = pi.i2c_read_byte(2) # read a byte from device 2
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_I2CRS, handle, 0))

   def i2c_write_byte_data(self, handle, reg, byte_val):
      """
      Writes a single byte to the specified register of the device
      associated with handle.

        handle:= >=0 (as returned by a prior call to [*i2c_open*]).
           reg:= >=0, the device register.
      byte_val:= 0-255, the value to write.

      SMBus 2.0 5.5.4 - Write byte.
      . .
      S Addr Wr [A] reg [A] byte_val [A] P
      . .

      ...
      # send byte 0xC5 to reg 2 of device 1
      pi.i2c_write_byte_data(1, 2, 0xC5)

      # send byte 9 to reg 4 of device 2
      pi.i2c_write_byte_data(2, 4, 9)
      ...
      """
      # I p1 handle
      # I p2 reg
      # I p3 4
      ## extension ##
      # I byte_val
      extents = [struct.pack("I", byte_val)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_I2CWB, handle, reg, 4, extents))

   def i2c_write_word_data(self, handle, reg, word_val):
      """
      Writes a single 16 bit word to the specified register of the
      device associated with handle.

        handle:= >=0 (as returned by a prior call to [*i2c_open*]).
           reg:= >=0, the device register.
      word_val:= 0-65535, the value to write.

      SMBus 2.0 5.5.4 - Write word.
      . .
      S Addr Wr [A] reg [A] word_val_Low [A] word_val_High [A] P
      . .

      ...
      # send word 0xA0C5 to reg 5 of device 4
      pi.i2c_write_word_data(4, 5, 0xA0C5)

      # send word 2 to reg 2 of device 5
      pi.i2c_write_word_data(5, 2, 23)
      ...
      """
      # I p1 handle
      # I p2 reg
      # I p3 4
      ## extension ##
      # I word_val
      extents = [struct.pack("I", word_val)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_I2CWW, handle, reg, 4, extents))

   def i2c_read_byte_data(self, handle, reg):
      """
      Reads a single byte from the specified register of the device
      associated with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
         reg:= >=0, the device register.

      SMBus 2.0 5.5.5 - Read byte.
      . .
      S Addr Wr [A] reg [A] S Addr Rd [A] [Data] NA P
      . .

      ...
      # read byte from reg 17 of device 2
      b = pi.i2c_read_byte_data(2, 17)

      # read byte from reg  1 of device 0
      b = pi.i2c_read_byte_data(0, 1)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_I2CRB, handle, reg))

   def i2c_read_word_data(self, handle, reg):
      """
      Reads a single 16 bit word from the specified register of the
      device associated with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
         reg:= >=0, the device register.

      SMBus 2.0 5.5.5 - Read word.
      . .
      S Addr Wr [A] reg [A] S Addr Rd [A] [DataLow] A [DataHigh] NA P
      . .

      ...
      # read word from reg 2 of device 3
      w = pi.i2c_read_word_data(3, 2)

      # read word from reg 7 of device 2
      w = pi.i2c_read_word_data(2, 7)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_I2CRW, handle, reg))

   def i2c_process_call(self, handle, reg, word_val):
      """
      Writes 16 bits of data to the specified register of the device
      associated with handle and reads 16 bits of data in return.

        handle:= >=0 (as returned by a prior call to [*i2c_open*]).
           reg:= >=0, the device register.
      word_val:= 0-65535, the value to write.

      SMBus 2.0 5.5.6 - Process call.
      . .
      S Addr Wr [A] reg [A] word_val_Low [A] word_val_High [A]
         S Addr Rd [A] [DataLow] A [DataHigh] NA P
      . .

      ...
      r = pi.i2c_process_call(h, 4, 0x1231)
      r = pi.i2c_process_call(h, 6, 0)
      ...
      """
      # I p1 handle
      # I p2 reg
      # I p3 4
      ## extension ##
      # I word_val
      extents = [struct.pack("I", word_val)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_I2CPC, handle, reg, 4, extents))

   def i2c_write_block_data(self, handle, reg, data):
      """
      Writes up to 32 bytes to the specified register of the device
      associated with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
         reg:= >=0, the device register.
        data:= the bytes to write.

      SMBus 2.0 5.5.7 - Block write.
      . .
      S Addr Wr [A] reg [A] len(data) [A] data0 [A] data1 [A] ... [A]
         datan [A] P
      . .

      ...
      pi.i2c_write_block_data(4, 5, b'hello')

      pi.i2c_write_block_data(4, 5, "data bytes")

      pi.i2c_write_block_data(5, 0, b'\\x00\\x01\\x22')

      pi.i2c_write_block_data(6, 2, [0, 1, 0x22])
      ...
      """
      # I p1 handle
      # I p2 reg
      # I p3 len
      ## extension ##
      # s len data bytes
      if len(data):
         return _u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_I2CWK, handle, reg, len(data), [data]))
      else:
         return 0

   def i2c_read_block_data(self, handle, reg):
      """
      Reads a block of up to 32 bytes from the specified register of
      the device associated with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
         reg:= >=0, the device register.

      SMBus 2.0 5.5.7 - Block read.
      . .
      S Addr Wr [A] reg [A]
         S Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P
      . .

      The amount of returned data is set by the device.

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (b, d) = pi.i2c_read_block_data(h, 10)
      if b >= 0:
         # process data
      else:
         # process read failure
      ...
      """
      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command(self.sl, _PI_CMD_I2CRK, handle, reg))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def i2c_block_process_call(self, handle, reg, data):
      """
      Writes data bytes to the specified register of the device
      associated with handle and reads a device specified number
      of bytes of data in return.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
         reg:= >=0, the device register.
        data:= the bytes to write.

      The SMBus 2.0 documentation states that a minimum of 1 byte may
      be sent and a minimum of 1 byte may be received.  The total
      number of bytes sent/received must be 32 or less.

      SMBus 2.0 5.5.8 - Block write-block read.
      . .
      S Addr Wr [A] reg [A] len(data) [A] data0 [A] ... datan [A]
         S Addr Rd [A] [Count] A [Data] ... A P
      . .

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (b, d) = pi.i2c_block_process_call(h, 10, b'\\x02\\x05\\x00')

      (b, d) = pi.i2c_block_process_call(h, 10, b'abcdr')

      (b, d) = pi.i2c_block_process_call(h, 10, "abracad")

      (b, d) = pi.i2c_block_process_call(h, 10, [2, 5, 16])
      ...
      """
      # I p1 handle
      # I p2 reg
      # I p3 len
      ## extension ##
      # s len data bytes

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_I2CPK, handle, reg, len(data), [data]))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def i2c_write_i2c_block_data(self, handle, reg, data):
      """
      Writes data bytes to the specified register of the device
      associated with handle .  1-32 bytes may be written.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
         reg:= >=0, the device register.
        data:= the bytes to write.

      . .
      S Addr Wr [A] reg [A] data0 [A] data1 [A] ... [A] datan [NA] P
      . .

      ...
      pi.i2c_write_i2c_block_data(4, 5, 'hello')

      pi.i2c_write_i2c_block_data(4, 5, b'hello')

      pi.i2c_write_i2c_block_data(5, 0, b'\\x00\\x01\\x22')

      pi.i2c_write_i2c_block_data(6, 2, [0, 1, 0x22])
      ...
      """
      # I p1 handle
      # I p2 reg
      # I p3 len
      ## extension ##
      # s len data bytes
      if len(data):
         return _u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_I2CWI, handle, reg, len(data), [data]))
      else:
         return 0

   def i2c_read_i2c_block_data(self, handle, reg, count):
      """
      Reads count bytes from the specified register of the device
      associated with handle .  The count may be 1-32.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
         reg:= >=0, the device register.
       count:= >0, the number of bytes to read.

      . .
      S Addr Wr [A] reg [A]
         S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
      . .

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (b, d) = pi.i2c_read_i2c_block_data(h, 4, 32)
      if b >= 0:
         # process data
      else:
         # process read failure
      ...
      """
      # I p1 handle
      # I p2 reg
      # I p3 4
      ## extension ##
      # I count
      extents = [struct.pack("I", count)]

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_I2CRI, handle, reg, 4, extentse))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def i2c_read_device(self, handle, count):
      """
      Returns count bytes read from the raw device associated
      with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
       count:= >0, the number of bytes to read.

      . .
      S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
      . .

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (count, data) = pi.i2c_read_device(h, 12)
      ...
      """
      self.sl.l.acquire()
      try:
         bytes = u2i(
            _pigpio_command(self.sl, _PI_CMD_I2CRD, handle, count))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def i2c_write_device(self, handle, data):
      """
      Writes the data bytes to the raw device associated with handle.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
        data:= the bytes to write.

      . .
      S Addr Wr [A] data0 [A] data1 [A] ... [A] datan [A] P
      . .

      ...
      pi.i2c_write_device(h, b"\\x12\\x34\\xA8")

      pi.i2c_write_device(h, b"help")

      pi.i2c_write_device(h, 'help')

      pi.i2c_write_device(h, [23, 56, 231])
      ...
      """
      # I p1 handle
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes
      if len(data):
         return _u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_I2CWD, handle, 0, len(data), [data]))
      else:
         return 0


   def i2c_zip(self, handle, data):
      """
      This function executes a sequence of I2C operations.  The
      operations to be performed are specified by the contents of data
      which contains the concatenated command codes and associated data.

      handle:= >=0 (as returned by a prior call to [*i2c_open*]).
        data:= the concatenated I2C commands, see below

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (count, data) = pi.i2c_zip(h, [4, 0x53, 7, 1, 0x32, 6, 6, 0])
      ...

      The following command codes are supported:

      Name    @ Cmd & Data @ Meaning
      End     @ 0          @ No more commands
      Escape  @ 1          @ Next P is two bytes
      On      @ 2          @ Switch combined flag on
      Off     @ 3          @ Switch combined flag off
      Address @ 4 P        @ Set I2C address to P
      Flags   @ 5 lsb msb  @ Set I2C flags to lsb + (msb << 8)
      Read    @ 6 P        @ Read P bytes of data
      Write   @ 7 P ...    @ Write P bytes of data

      The address, read, and write commands take a parameter P.
      Normally P is one byte (0-255).  If the command is preceded by
      the Escape command then P is two bytes (0-65535, least significant
      byte first).

      The address defaults to that associated with the handle.
      The flags default to 0.  The address and flags maintain their
      previous value until updated.

      Any read I2C data is concatenated in the returned bytearray.

      ...
      Set address 0x53, write 0x32, read 6 bytes
      Set address 0x1E, write 0x03, read 6 bytes
      Set address 0x68, write 0x1B, read 8 bytes
      End

      0x04 0x53   0x07 0x01 0x32   0x06 0x06
      0x04 0x1E   0x07 0x01 0x03   0x06 0x06
      0x04 0x68   0x07 0x01 0x1B   0x06 0x08
      0x00
      ...
      """
      # I p1 handle
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_I2CZ, handle, 0, len(data), [data]))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data


   def bb_spi_open(self, CS, MISO, MOSI, SCLK, baud=100000, spi_flags=0):
      """
      This function selects a set of GPIO for bit banging SPI at a
      specified baud rate.

            CS := 0-31
          MISO := 0-31
          MOSI := 0-31
          SCLK := 0-31
          baud := 50-250000
      spiFlags := see below
      
      spiFlags consists of the least significant 22 bits.

      . .
      21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
       0  0  0  0  0  0  R  T  0  0  0  0  0  0  0  0  0  0  0  p  m  m
      . .

      mm defines the SPI mode, defaults to 0

      . .
      Mode CPOL CPHA
       0     0    0
       1     0    1
       2     1    0
       3     1    1
      . .

      The following constants may be used to set the mode:

      . .
      pigpio.SPI_MODE_0
      pigpio.SPI_MODE_1
      pigpio.SPI_MODE_2
      pigpio.SPI_MODE_3
      . .

      Alternatively pigpio.SPI_CPOL and/or pigpio.SPI_CPHA
      may be used.

      p is 0 if CS is active low (default) and 1 for active high.
      pigpio.SPI_CS_HIGH_ACTIVE may be used to set this flag.

      T is 1 if the least significant bit is transmitted on MOSI first,
      the default (0) shifts the most significant bit out first.
      pigpio.SPI_TX_LSBFIRST may be used to set this flag.

      R is 1 if the least significant bit is received on MISO first,
      the default (0) receives the most significant bit first.
      pigpio.SPI_RX_LSBFIRST may be used to set this flag.

      The other bits in spiFlags should be set to zero.

      Returns 0 if OK, otherwise PI_BAD_USER_GPIO, PI_BAD_SPI_BAUD, or
      PI_GPIO_IN_USE.

      If more than one device is connected to the SPI bus (defined by
      SCLK, MOSI, and MISO) each must have its own CS.

      ...
      bb_spi_open(10, MISO, MOSI, SCLK, 10000, 0); // device 1
      bb_spi_open(11, MISO, MOSI, SCLK, 20000, 3); // device 2
      ...
      """
      # I p1 CS
      # I p2 0
      # I p3 20
      ## extension ##
      # I MISO
      # I MOSI
      # I SCLK
      # I baud
      # I spi_flags
      
      extents = [struct.pack("IIIII", MISO, MOSI, SCLK, baud, spi_flags)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_BSPIO, CS, 0, 20, extents))


   def bb_spi_close(self, CS):
      """
      This function stops bit banging SPI on a set of GPIO
      opened with [*bb_spi_open*].

      CS:= 0-31, the CS GPIO used in a prior call to [*bb_spi_open*]

      Returns 0 if OK, otherwise PI_BAD_USER_GPIO, or PI_NOT_SPI_GPIO.

      ...
      pi.bb_spi_close(CS)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_BSPIC, CS, 0))


   def bb_spi_xfer(self, CS, data):
      """
      This function executes a bit banged SPI transfer.

        CS:= 0-31 (as used in a prior call to [*bb_spi_open*])
      data:= data to be sent

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      #!/usr/bin/env python

      import pigpio

      CE0=5
      CE1=6
      MISO=13
      MOSI=19
      SCLK=12

      pi = pigpio.pi()
      if not pi.connected:
         exit()

      pi.bb_spi_open(CE0, MISO, MOSI, SCLK, 10000, 0) # MCP4251 DAC
      pi.bb_spi_open(CE1, MISO, MOSI, SCLK, 20000, 3) # MCP3008 ADC

      for i in range(256):

         count, data = pi.bb_spi_xfer(CE0, [0, i]) # Set DAC value

         if count == 2:

            count, data = pi.bb_spi_xfer(CE0, [12, 0]) # Read back DAC

            if count == 2:

               set_val = data[1]

               count, data = pi.bb_spi_xfer(CE1, [1, 128, 0]) # Read ADC

               if count == 3:

                  read_val = ((data[1]&3)<<8) | data[2]

                  print("{} {}".format(set_val, read_val))

      pi.bb_spi_close(CE0)
      pi.bb_spi_close(CE1)

      pi.stop()
      ...
      """
      # I p1 CS
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_BSPIX, CS, 0, len(data), [data]))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data


   def bb_i2c_open(self, SDA, SCL, baud=100000):
      """
      This function selects a pair of GPIO for bit banging I2C at a
      specified baud rate.

      Bit banging I2C allows for certain operations which are not possible
      with the standard I2C driver.

      o baud rates as low as 50 
      o repeated starts 
      o clock stretching 
      o I2C on any pair of spare GPIO

       SDA:= 0-31
       SCL:= 0-31
      baud:= 50-500000

      Returns 0 if OK, otherwise PI_BAD_USER_GPIO, PI_BAD_I2C_BAUD, or
      PI_GPIO_IN_USE.

      NOTE:

      The GPIO used for SDA and SCL must have pull-ups to 3V3 connected.
      As a guide the hardware pull-ups on pins 3 and 5 are 1k8 in value.

      ...
      h = pi.bb_i2c_open(4, 5, 50000) # bit bang on GPIO 4/5 at 50kbps
      ...
      """
      # I p1 SDA
      # I p2 SCL
      # I p3 4
      ## extension ##
      # I baud
      extents = [struct.pack("I", baud)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_BI2CO, SDA, SCL, 4, extents))


   def bb_i2c_close(self, SDA):
      """
      This function stops bit banging I2C on a pair of GPIO
      previously opened with [*bb_i2c_open*].

      SDA:= 0-31, the SDA GPIO used in a prior call to [*bb_i2c_open*]

      Returns 0 if OK, otherwise PI_BAD_USER_GPIO, or PI_NOT_I2C_GPIO.

      ...
      pi.bb_i2c_close(SDA)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_BI2CC, SDA, 0))


   def bb_i2c_zip(self, SDA, data):
      """
      This function executes a sequence of bit banged I2C operations.
      The operations to be performed are specified by the contents
      of data which contains the concatenated command codes and
      associated data.

       SDA:= 0-31 (as used in a prior call to [*bb_i2c_open*])
      data:= the concatenated I2C commands, see below

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (count, data) = pi.bb_i2c_zip(
                         SDA, [4, 0x53, 2, 7, 1, 0x32, 2, 6, 6, 3, 0])
      ...

      The following command codes are supported:

      Name    @ Cmd & Data   @ Meaning
      End     @ 0            @ No more commands
      Escape  @ 1            @ Next P is two bytes
      Start   @ 2            @ Start condition
      Stop    @ 3            @ Stop condition
      Address @ 4 P          @ Set I2C address to P
      Flags   @ 5 lsb msb    @ Set I2C flags to lsb + (msb << 8)
      Read    @ 6 P          @ Read P bytes of data
      Write   @ 7 P ...      @ Write P bytes of data

      The address, read, and write commands take a parameter P.
      Normally P is one byte (0-255).  If the command is preceded by
      the Escape command then P is two bytes (0-65535, least significant
      byte first).

      The address and flags default to 0.  The address and flags maintain
      their previous value until updated.

      No flags are currently defined.

      Any read I2C data is concatenated in the returned bytearray.

      ...
      Set address 0x53
      start, write 0x32, (re)start, read 6 bytes, stop
      Set address 0x1E
      start, write 0x03, (re)start, read 6 bytes, stop
      Set address 0x68
      start, write 0x1B, (re)start, read 8 bytes, stop
      End

      0x04 0x53
      0x02 0x07 0x01 0x32   0x02 0x06 0x06 0x03

      0x04 0x1E
      0x02 0x07 0x01 0x03   0x02 0x06 0x06 0x03

      0x04 0x68
      0x02 0x07 0x01 0x1B   0x02 0x06 0x08 0x03

      0x00
      ...
      """
      # I p1 SDA
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_BI2CZ, SDA, 0, len(data), [data]))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def event_trigger(self, event):
      """
      This function signals the occurrence of an event.

      event:= 0-31, the event

      Returns 0 if OK, otherwise PI_BAD_EVENT_ID.

      An event is a signal used to inform one or more consumers
      to start an action.  Each consumer which has registered an
      interest in the event (e.g. by calling [*event_callback*]) will
      be informed by a callback.

      One event, EVENT_BSC (31) is predefined.  This event is
      auto generated on BSC slave activity.

      The meaning of other events is arbitrary.

      Note that other than its id and its tick there is no data associated
      with an event.

      ...
      pi.event_trigger(23)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_EVT, event, 0))


   def bsc_xfer(self, bsc_control, data):
      """
      This function provides a low-level interface to the
      SPI/I2C Slave peripheral.  This peripheral allows the
      Pi to act as a slave device on an I2C or SPI bus.

      I can't get SPI to work properly.  I tried with a
      control word of 0x303 and swapped MISO and MOSI.


      The function sets the BSC mode, writes any data in
      the transmit buffer to the BSC transmit FIFO, and
      copies any data in the BSC receive FIFO to the
      receive buffer.

      bsc_control:= see below
             data:= the data bytes to place in the transmit FIFO.

      The returned value is a tuple of the status (see below),
      the number of bytes read, and a bytearray containing the
      read bytes.  If there was an error the status will be less
      than zero (and will contain the error code).

      Note that the control word sets the BSC mode.  The BSC will
      stay in that mode until a different control word is sent.

      The BSC peripheral uses GPIO 18 (SDA) and 19 (SCL)
      in I2C mode and GPIO 18 (MOSI), 19 (SCLK), 20 (MISO),
      and 21 (CE) in SPI mode.  You need to swap MISO/MOSI
      between master and slave.

      When a zero control word is received GPIO 18-21 will be reset
      to INPUT mode.

      bsc_control consists of the following bits:

      . .
      22 21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
       a  a  a  a  a  a  a  -  - IT HC TF IR RE TE BK EC ES PL PH I2 SP EN
      . .

      Bits 0-13 are copied unchanged to the BSC CR register.  See
      pages 163-165 of the Broadcom peripherals document for full
      details.

      aaaaaaa @ defines the I2C slave address (only relevant in I2C mode)
      IT      @ invert transmit status flags
      HC      @ enable host control
      TF      @ enable test FIFO
      IR      @ invert receive status flags
      RE      @ enable receive
      TE      @ enable transmit
      BK      @ abort operation and clear FIFOs
      EC      @ send control register as first I2C byte
      ES      @ send status register as first I2C byte
      PL      @ set SPI polarity high
      PH      @ set SPI phase high
      I2      @ enable I2C mode
      SP      @ enable SPI mode
      EN      @ enable BSC peripheral

      The status has the following format:

      . .
      20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
       S  S  S  S  S  R  R  R  R  R  T  T  T  T  T RB TE RF TF RE TB
      . .

      Bits 0-15 are copied unchanged from the BSC FR register.  See
      pages 165-166 of the Broadcom peripherals document for full
      details.

      SSSSS @ number of bytes successfully copied to transmit FIFO
      RRRRR @ number of bytes in receieve FIFO
      TTTTT @ number of bytes in transmit FIFO
      RB    @ receive busy
      TE    @ transmit FIFO empty
      RF    @ receive FIFO full
      TF    @ transmit FIFO full
      RE    @ receive FIFO empty
      TB    @ transmit busy

      ...
      (status, count, data) = pi.bsc_xfer(0x330305, "Hello!")
      ...
      """
      # I p1 control
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_BSCX, bsc_control, 0, len(data), [data]))
         if bytes > 0:
            rx = self._rxbuf(bytes)
            status = struct.unpack('I', rx[0:4])[0]
            bytes -= 4
            data = rx[4:]
         else:
            status = bytes
            bytes = 0
            data = bytearray(b'')
      finally:
         self.sl.l.release()
      return status, bytes, data

   def bsc_i2c(self, i2c_address, data=[]):
      """
      This function allows the Pi to act as a slave I2C device.

      The data bytes (if any) are written to the BSC transmit
      FIFO and the bytes in the BSC receive FIFO are returned.

      i2c_address:= the I2C slave address.
             data:= the data bytes to transmit.

      The returned value is a tuple of the status, the number
      of bytes read, and a bytearray containing the read bytes.

      See [*bsc_xfer*] for details of the status value.

      If there was an error the status will be less than zero
      (and will contain the error code).

      Note that an i2c_address of 0 may be used to close
      the BSC device and reassign the used GPIO (18/19)
      as inputs.

      This example assumes GPIO 2/3 are connected to GPIO 18/19.

      ...
      #!/usr/bin/env python
      import time
      import pigpio

      I2C_ADDR=0x13

      def i2c(id, tick):
          global pi

          s, b, d = pi.bsc_i2c(I2C_ADDR)
          if b:
              if d[0] == ord('t'): # 116 send 'HH:MM:SS*'

                  print("sent={} FR={} received={} [{}]".
                     format(s>>16, s&0xfff,b,d))

                  s, b, d = pi.bsc_i2c(I2C_ADDR,
                     "{}*".format(time.asctime()[11:19]))

              elif d[0] == ord('d'): # 100 send 'Sun Oct 30*'

                  print("sent={} FR={} received={} [{}]".
                     format(s>>16, s&0xfff,b,d))

                  s, b, d = pi.bsc_i2c(I2C_ADDR,
                     "{}*".format(time.asctime()[:10]))

      pi = pigpio.pi()

      if not pi.connected:
          exit()

      # Respond to BSC slave activity

      e = pi.event_callback(pigpio.EVENT_BSC, i2c)

      pi.bsc_i2c(I2C_ADDR) # Configure BSC as I2C slave

      time.sleep(600)

      e.cancel()

      pi.bsc_i2c(0) # Disable BSC peripheral

      pi.stop()
      ...

      While running the above.

      . .
      $ i2cdetect -y 1
          0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
      00:          -- -- -- -- -- -- -- -- -- -- -- -- --
      10: -- -- -- 13 -- -- -- -- -- -- -- -- -- -- -- --
      20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
      30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
      40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
      50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
      60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
      70: -- -- -- -- -- -- -- --

      $ pigs i2co 1 0x13 0
      0

      $ pigs i2cwd 0 116
      $ pigs i2crd 0 9 -a
      9 10:13:58*

      $ pigs i2cwd 0 116
      $ pigs i2crd 0 9 -a
      9 10:14:29*

      $ pigs i2cwd 0 100
      $ pigs i2crd 0 11 -a
      11 Sun Oct 30*

      $ pigs i2cwd 0 100
      $ pigs i2crd 0 11 -a
      11 Sun Oct 30*

      $ pigs i2cwd 0 116
      $ pigs i2crd 0 9 -a
      9 10:23:16*

      $ pigs i2cwd 0 100
      $ pigs i2crd 0 11 -a
      11 Sun Oct 30*
      . .
      """
      if i2c_address:
         control = (i2c_address<<16)|0x305
      else:
         control = 0
      return self.bsc_xfer(control, data)

   def spi_open(self, spi_channel, baud, spi_flags=0):
      """
      Returns a handle for the SPI device on channel.  Data will be
      transferred at baud bits per second.  The flags may be used to
      modify the default behaviour of 4-wire operation, mode 0,
      active low chip select.

      An auxiliary SPI device is available on all models but the
      A and B and may be selected by setting the A bit in the
      flags. The auxiliary device has 3 chip selects and a
      selectable word size in bits.

      spi_channel:= 0-1 (0-2 for the auxiliary SPI device).
             baud:= 32K-125M (values above 30M are unlikely to work).
        spi_flags:= see below.

      Normally you would only use the [*spi_**] functions if
      you are or will be connecting to the Pi over a network.  If
      you will always run on the local Pi use the standard SPI
      module instead.

      spi_flags consists of the least significant 22 bits.

      . .
      21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
       b  b  b  b  b  b  R  T  n  n  n  n  W  A u2 u1 u0 p2 p1 p0  m  m
      . .

      mm defines the SPI mode.

      WARNING: modes 1 and 3 do not appear to work on
      the auxiliary device.

      . .
      Mode POL PHA
       0    0   0
       1    0   1
       2    1   0
       3    1   1
      . .

      px is 0 if CEx is active low (default) and 1 for active high.

      ux is 0 if the CEx GPIO is reserved for SPI (default)
      and 1 otherwise.

      A is 0 for the standard SPI device, 1 for the auxiliary SPI.

      W is 0 if the device is not 3-wire, 1 if the device is 3-wire.
      Standard SPI device only.

      nnnn defines the number of bytes (0-15) to write before
      switching the MOSI line to MISO to read data.  This field
      is ignored if W is not set.  Standard SPI device only.

      T is 1 if the least significant bit is transmitted on MOSI
      first, the default (0) shifts the most significant bit out
      first.  Auxiliary SPI device only.

      R is 1 if the least significant bit is received on MISO
      first, the default (0) receives the most significant bit
      first.  Auxiliary SPI device only.

      bbbbbb defines the word size in bits (0-32).  The default (0)
      sets 8 bits per word.  Auxiliary SPI device only.

      The [*spi_read*], [*spi_write*], and [*spi_xfer*] functions
      transfer data packed into 1, 2, or 4 bytes according to
      the word size in bits.

      For bits 1-8 there will be one byte per character. 
      For bits 9-16 there will be two bytes per character. 
      For bits 17-32 there will be four bytes per character.

      Multi-byte transfers are made in least significant byte
      first order.

      E.g. to transfer 32 11-bit words data should
      contain 64 bytes.

      E.g. to transfer the 14 bit value 0x1ABC send the
      bytes 0xBC followed by 0x1A.

      The other bits in flags should be set to zero.

      ...
      # open SPI device on channel 1 in mode 3 at 50000 bits per second

      h = pi.spi_open(1, 50000, 3)
      ...
      """
      # I p1 spi_channel
      # I p2 baud
      # I p3 4
      ## extension ##
      # I spi_flags
      extents = [struct.pack("I", spi_flags)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_SPIO, spi_channel, baud, 4, extents))

   def spi_close(self, handle):
      """
      Closes the SPI device associated with handle.

      handle:= >=0 (as returned by a prior call to [*spi_open*]).

      ...
      pi.spi_close(h)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_SPIC, handle, 0))

   def spi_read(self, handle, count):
      """
      Reads count bytes from the SPI device associated with handle.

      handle:= >=0 (as returned by a prior call to [*spi_open*]).
       count:= >0, the number of bytes to read.

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (b, d) = pi.spi_read(h, 60) # read 60 bytes from device h
      if b == 60:
         # process read data
      else:
         # error path
      ...
      """
      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command(
            self.sl, _PI_CMD_SPIR, handle, count))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def spi_write(self, handle, data):
      """
      Writes the data bytes to the SPI device associated with handle.

      handle:= >=0 (as returned by a prior call to [*spi_open*]).
        data:= the bytes to write.

      ...
      pi.spi_write(0, b'\\x02\\xc0\\x80') # write 3 bytes to device 0

      pi.spi_write(0, b'defgh')        # write 5 bytes to device 0

      pi.spi_write(0, "def")           # write 3 bytes to device 0

      pi.spi_write(1, [2, 192, 128])   # write 3 bytes to device 1
      ...
      """
      # I p1 handle
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_SPIW, handle, 0, len(data), [data]))

   def spi_xfer(self, handle, data):
      """
      Writes the data bytes to the SPI device associated with handle,
      returning the data bytes read from the device.

      handle:= >=0 (as returned by a prior call to [*spi_open*]).
        data:= the bytes to write.

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (count, rx_data) = pi.spi_xfer(h, b'\\x01\\x80\\x00')

      (count, rx_data) = pi.spi_xfer(h, [1, 128, 0])

      (count, rx_data) = pi.spi_xfer(h, b"hello")

      (count, rx_data) = pi.spi_xfer(h, "hello")
      ...
      """
      # I p1 handle
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_SPIX, handle, 0, len(data), [data]))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def serial_open(self, tty, baud, ser_flags=0):
      """
      Returns a handle for the serial tty device opened
      at baud bits per second.  The device name must start
      with /dev/tty or /dev/serial.

            tty:= the serial device to open.
           baud:= baud rate in bits per second, see below.
      ser_flags:= 0, no flags are currently defined.

      Normally you would only use the [*serial_**] functions if
      you are or will be connecting to the Pi over a network.  If
      you will always run on the local Pi use the standard serial
      module instead.

      The baud rate must be one of 50, 75, 110, 134, 150,
      200, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200,
      38400, 57600, 115200, or 230400.

      ...
      h1 = pi.serial_open("/dev/ttyAMA0", 300)

      h2 = pi.serial_open("/dev/ttyUSB1", 19200, 0)

      h3 = pi.serial_open("/dev/serial0", 9600)
      ...
      """
      # I p1 baud
      # I p2 ser_flags
      # I p3 len
      ## extension ##
      # s len data bytes
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_SERO, baud, ser_flags, len(tty), [tty]))

   def serial_close(self, handle):
      """
      Closes the serial device associated with handle.

      handle:= >=0 (as returned by a prior call to [*serial_open*]).

      ...
      pi.serial_close(h1)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_SERC, handle, 0))

   def serial_read_byte(self, handle):
      """
      Returns a single byte from the device associated with handle.

      handle:= >=0 (as returned by a prior call to [*serial_open*]).

      If no data is ready a negative error code will be returned.

      ...
      b = pi.serial_read_byte(h1)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_SERRB, handle, 0))

   def serial_write_byte(self, handle, byte_val):
      """
      Writes a single byte to the device associated with handle.

        handle:= >=0 (as returned by a prior call to [*serial_open*]).
      byte_val:= 0-255, the value to write.

      ...
      pi.serial_write_byte(h1, 23)

      pi.serial_write_byte(h1, ord('Z'))
      ...
      """
      return _u2i(
         _pigpio_command(self.sl, _PI_CMD_SERWB, handle, byte_val))

   def serial_read(self, handle, count=1000):
      """
      Reads up to count bytes from the device associated with handle.

      handle:= >=0 (as returned by a prior call to [*serial_open*]).
       count:= >0, the number of bytes to read (defaults to 1000).

      The returned value is a tuple of the number of bytes read and
      a bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      If no data is ready a bytes read of zero is returned.
      ...
      (b, d) = pi.serial_read(h2, 100)
      if b > 0:
         # process read data
      ...
      """
      self.sl.l.acquire()
      try:
         bytes = u2i(
            _pigpio_command(self.sl, _PI_CMD_SERR, handle, count))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def serial_write(self, handle, data):
      """
      Writes the data bytes to the device associated with handle.

      handle:= >=0 (as returned by a prior call to [*serial_open*]).
        data:= the bytes to write.

      ...
      pi.serial_write(h1, b'\\x02\\x03\\x04')

      pi.serial_write(h2, b'help')

      pi.serial_write(h2, "hello")

      pi.serial_write(h1, [2, 3, 4])
      ...
      """
      # I p1 handle
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_SERW, handle, 0, len(data), [data]))

   def serial_data_available(self, handle):
      """
      Returns the number of bytes available to be read from the
      device associated with handle.

      handle:= >=0 (as returned by a prior call to [*serial_open*]).

      ...
      rdy = pi.serial_data_available(h1)

      if rdy > 0:
         (b, d) = pi.serial_read(h1, rdy)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_SERDA, handle, 0))

   def gpio_trigger(self, user_gpio, pulse_len=10, level=1):
      """
      Send a trigger pulse to a GPIO.  The GPIO is set to
      level for pulse_len microseconds and then reset to not level.

      user_gpio:= 0-31
      pulse_len:= 1-100
          level:= 0-1

      ...
      pi.gpio_trigger(23, 10, 1)
      ...
      """
      # pigpio message format

      # I p1 user_gpio
      # I p2 pulse_len
      # I p3 4
      ## extension ##
      # I level
      extents = [struct.pack("I", level)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_TRIG, user_gpio, pulse_len, 4, extents))

   def set_glitch_filter(self, user_gpio, steady):
      """
      Sets a glitch filter on a GPIO.

      Level changes on the GPIO are not reported unless the level
      has been stable for at least [*steady*] microseconds.  The
      level is then reported.  Level changes of less than [*steady*]
      microseconds are ignored.

      user_gpio:= 0-31
         steady:= 0-300000

      Returns 0 if OK, otherwise PI_BAD_USER_GPIO, or PI_BAD_FILTER.

      This filter affects the GPIO samples returned to callbacks set up
      with [*callback*] and [*wait_for_edge*].

      It does not affect levels read by [*read*],
      [*read_bank_1*], or [*read_bank_2*].

      Each (stable) edge will be timestamped [*steady*]
      microseconds after it was first detected.

      ...
      pi.set_glitch_filter(23, 100)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_FG, user_gpio, steady))

   def set_noise_filter(self, user_gpio, steady, active):
      """
      Sets a noise filter on a GPIO.

      Level changes on the GPIO are ignored until a level which has
      been stable for [*steady*] microseconds is detected.  Level
      changes on the GPIO are then reported for [*active*]
      microseconds after which the process repeats.

      user_gpio:= 0-31
         steady:= 0-300000
         active:= 0-1000000

      Returns 0 if OK, otherwise PI_BAD_USER_GPIO, or PI_BAD_FILTER.

      This filter affects the GPIO samples returned to callbacks set up
      with [*callback*] and [*wait_for_edge*].

      It does not affect levels read by [*read*],
      [*read_bank_1*], or [*read_bank_2*].

      Level changes before and after the active period may
      be reported.  Your software must be designed to cope with
      such reports.

      ...
      pi.set_noise_filter(23, 1000, 5000)
      ...
      """
      # pigpio message format

      # I p1 user_gpio
      # I p2 steady
      # I p3 4
      ## extension ##
      # I active
      extents = [struct.pack("I", active)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_FN, user_gpio, steady, 4, extents))

   def store_script(self, script):
      """
      Store a script for later execution.

      See [[http://abyz.me.uk/rpi/pigpio/pigs.html#Scripts]] for
      details.

      script:= the script text as a series of bytes.

      Returns a >=0 script id if OK.

      ...
      sid = pi.store_script(
         b'tag 0 w 22 1 mils 100 w 22 0 mils 100 dcr p0 jp 0')
      ...
      """
      # I p1 0
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes
      if len(script):
         return _u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_PROC, 0, 0, len(script), [script]))
      else:
         return 0

   def run_script(self, script_id, params=None):
      """
      Runs a stored script.

      script_id:= id of stored script.
         params:= up to 10 parameters required by the script.

      ...
      s = pi.run_script(sid, [par1, par2])

      s = pi.run_script(sid)

      s = pi.run_script(sid, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
      ...
      """
      # I p1 script id
      # I p2 0
      # I p3 params * 4 (0-10 params)
      ## (optional) extension ##
      # I[] params
      if params is not None:
         ext = bytearray()
         for p in params:
            ext.extend(struct.pack("I", p))
         nump = len(params)
         extents = [ext]
      else:
         nump = 0
         extents = []
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_PROCR, script_id, 0, nump*4, extents))

   def script_status(self, script_id):
      """
      Returns the run status of a stored script as well as the
      current values of parameters 0 to 9.

      script_id:= id of stored script.

      The run status may be

      . .
      PI_SCRIPT_INITING
      PI_SCRIPT_HALTED
      PI_SCRIPT_RUNNING
      PI_SCRIPT_WAITING
      PI_SCRIPT_FAILED
      . .

      The return value is a tuple of run status and a list of
      the 10 parameters.  On error the run status will be negative
      and the parameter list will be empty.

      ...
      (s, pars) = pi.script_status(sid)
      ...
      """
      self.sl.l.acquire()
      try:
         bytes = u2i(
            _pigpio_command(self.sl, _PI_CMD_PROCP, script_id, 0))
         if bytes > 0:
            data = self._rxbuf(bytes)
            pars = struct.unpack('11i', _str(data))
            status = pars[0]
            params = pars[1:]
         else:
            status = bytes
            params = ()
      finally:
         self.sl.l.release()
      return status, params

   def stop_script(self, script_id):
      """
      Stops a running script.

      script_id:= id of stored script.

      ...
      status = pi.stop_script(sid)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PROCS, script_id, 0))

   def delete_script(self, script_id):
      """
      Deletes a stored script.

      script_id:= id of stored script.

      ...
      status = pi.delete_script(sid)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PROCD, script_id, 0))

   def bb_serial_read_open(self, user_gpio, baud, bb_bits=8):
      """
      Opens a GPIO for bit bang reading of serial data.

      user_gpio:= 0-31, the GPIO to use.
           baud:= 50-250000, the baud rate.
        bb_bits:= 1-32, the number of bits per word, default 8.

      The serial data is held in a cyclic buffer and is read using
      [*bb_serial_read*].

      It is the caller's responsibility to read data from the cyclic
      buffer in a timely fashion.

      ...
      status = pi.bb_serial_read_open(4, 19200)
      status = pi.bb_serial_read_open(17, 9600)
      ...
      """
      # pigpio message format

      # I p1 user_gpio
      # I p2 baud
      # I p3 4
      ## extension ##
      # I bb_bits
      extents = [struct.pack("I", bb_bits)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_SLRO, user_gpio, baud, 4, extents))

   def bb_serial_read(self, user_gpio):
      """
      Returns data from the bit bang serial cyclic buffer.

      user_gpio:= 0-31 (opened in a prior call to [*bb_serial_read_open*])

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      The bytes returned for each character depend upon the number of
      data bits [*bb_bits*] specified in the [*bb_serial_read_open*]
      command.

      For [*bb_bits*] 1-8 there will be one byte per character. 
      For [*bb_bits*] 9-16 there will be two bytes per character. 
      For [*bb_bits*] 17-32 there will be four bytes per character.

      ...
      (count, data) = pi.bb_serial_read(4)
      ...
      """
      self.sl.l.acquire()
      try:
          bytes = u2i(
             _pigpio_command(self.sl, _PI_CMD_SLR, user_gpio, 10000))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   
   def bb_serial_read_close(self, user_gpio):
      """
      Closes a GPIO for bit bang reading of serial data.

      user_gpio:= 0-31 (opened in a prior call to [*bb_serial_read_open*])

      ...
      status = pi.bb_serial_read_close(17)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_SLRC, user_gpio, 0))

   def bb_serial_invert(self, user_gpio, invert):
      """
      Invert serial logic.

      user_gpio:= 0-31 (opened in a prior call to [*bb_serial_read_open*])
          invert:= 0-1 (1 invert, 0 normal)

      ...
      status = pi.bb_serial_invert(17, 1)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_SLRI, user_gpio, invert))


   def custom_1(self, arg1=0, arg2=0, argx=[]):
      """
      Calls a pigpio function customised by the user.

      arg1:= >=0, default 0.
      arg2:= >=0, default 0.
      argx:= extra arguments (each 0-255), default empty.

      The returned value is an integer which by convention
      should be >=0 for OK and <0 for error.

      ...
      value = pi.custom_1()

      value = pi.custom_1(23)

      value = pi.custom_1(0, 55)

      value = pi.custom_1(23, 56, [1, 5, 7])

      value = pi.custom_1(23, 56, b"hello")

      value = pi.custom_1(23, 56, "hello")
      ...
      """
      # I p1 arg1
      # I p2 arg2
      # I p3 len
      ## extension ##
      # s len argx bytes

      return u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_CF1, arg1, arg2, len(argx), [argx]))

   def custom_2(self, arg1=0, argx=[], retMax=8192):
      """
      Calls a pigpio function customised by the user.

        arg1:= >=0, default 0.
        argx:= extra arguments (each 0-255), default empty.
      retMax:= >=0, maximum number of bytes to return, default 8192.

      The returned value is a tuple of the number of bytes
      returned and a bytearray containing the bytes.  If
      there was an error the number of bytes read will be
      less than zero (and will contain the error code).

      ...
      (count, data) = pi.custom_2()

      (count, data) = pi.custom_2(23)

      (count, data) = pi.custom_2(23, [1, 5, 7])

      (count, data) = pi.custom_2(23, b"hello")

      (count, data) = pi.custom_2(23, "hello", 128)
      ...
      """
      # I p1 arg1
      # I p2 retMax
      # I p3 len
      ## extension ##
      # s len argx bytes

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_CF2, arg1, retMax, len(argx), [argx]))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def get_pad_strength(self, pad):
      """
      This function returns the pad drive strength in mA.

      pad:= 0-2, the pad to get.

      Returns the pad drive strength if OK, otherwise PI_BAD_PAD.

      Pad @ GPIO
      0   @ 0-27
      1   @ 28-45
      2   @ 46-53

      ...
      strength = pi.get_pad_strength(0) # Get pad 0 strength.
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PADG, pad, 0))

   def set_pad_strength(self, pad, pad_strength):
      """
      This function sets the pad drive strength in mA.


               pad:= 0-2, the pad to set.
      pad_strength:= 1-16 mA.

      Returns 0 if OK, otherwise PI_BAD_PAD, or PI_BAD_STRENGTH.

      Pad @ GPIO
      0   @ 0-27
      1   @ 28-45
      2   @ 46-53

      ...
      pi.set_pad_strength(2, 14) # Set pad 2 to 14 mA.
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_PADS, pad, pad_strength))


   def file_open(self, file_name, file_mode):
      """
      This function returns a handle to a file opened in a specified mode.

      file_name:= the file to open.
      file_mode:= the file open mode.

      Returns a handle (>=0) if OK, otherwise PI_NO_HANDLE,
      PI_NO_FILE_ACCESS, PI_BAD_FILE_MODE,
      PI_FILE_OPEN_FAILED, or PI_FILE_IS_A_DIR.

      ...
      h = pi.file_open("/home/pi/shared/dir_3/file.txt",
              pigpio.FILE_WRITE | pigpio.FILE_CREATE)

      pi.file_write(h, "Hello world")

      pi.file_close(h)
      ...

      File

      A file may only be opened if permission is granted by an entry
      in /opt/pigpio/access.  This is intended to allow remote access
      to files in a more or less controlled manner.

      Each entry in /opt/pigpio/access takes the form of a file path
      which may contain wildcards followed by a single letter permission.
      The permission may be R for read, W for write, U for read/write,
      and N for no access.

      Where more than one entry matches a file the most specific rule
      applies.  If no entry matches a file then access is denied.

      Suppose /opt/pigpio/access contains the following entries:

      . .
      /home/* n
      /home/pi/shared/dir_1/* w
      /home/pi/shared/dir_2/* r
      /home/pi/shared/dir_3/* u
      /home/pi/shared/dir_1/file.txt n
      . .

      Files may be written in directory dir_1 with the exception
      of file.txt.

      Files may be read in directory dir_2.

      Files may be read and written in directory dir_3.

      If a directory allows read, write, or read/write access then files
      may be created in that directory.

      In an attempt to prevent risky permissions the following paths are
      ignored in /opt/pigpio/access:

      . .
      a path containing ..
      a path containing only wildcards (*?)
      a path containing less than two non-wildcard parts
      . .

      Mode

      The mode may have the following values:

      Constant   @ Value @ Meaning
      FILE_READ  @   1   @ open file for reading
      FILE_WRITE @   2   @ open file for writing
      FILE_RW    @   3   @ open file for reading and writing

      The following values may be or'd into the mode:

      Name        @ Value @ Meaning
      FILE_APPEND @ 4     @ All writes append data to the end of the file
      FILE_CREATE @ 8     @ The file is created if it doesn't exist
      FILE_TRUNC  @ 16    @ The file is truncated

      Newly created files are owned by root with permissions owner
      read and write.

      ...
      #!/usr/bin/env python

      import pigpio

      pi = pigpio.pi()

      if not pi.connected:
         exit()

      # Assumes /opt/pigpio/access contains the following line:
      # /ram/*.c r

      handle = pi.file_open("/ram/pigpio.c", pigpio.FILE_READ)

      done = False

      while not done:
         c, d = pi.file_read(handle, 60000)
         if c > 0:
            print(d)
         else:
            done = True

      pi.file_close(handle)

      pi.stop()
      ...
      """
      # I p1 file_mode
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_FO, file_mode, 0, len(file_name), [file_name]))

   def file_close(self, handle):
      """
      Closes the file associated with handle.

      handle:= >=0 (as returned by a prior call to [*file_open*]).

      ...
      pi.file_close(handle)
      ...
      """
      return _u2i(_pigpio_command(self.sl, _PI_CMD_FC, handle, 0))

   def file_read(self, handle, count):
      """
      Reads up to count bytes from the file associated with handle.

      handle:= >=0 (as returned by a prior call to [*file_open*]).
       count:= >0, the number of bytes to read.

      The returned value is a tuple of the number of bytes read and a
      bytearray containing the bytes.  If there was an error the
      number of bytes read will be less than zero (and will contain
      the error code).

      ...
      (b, d) = pi.file_read(h2, 100)
      if b > 0:
         # process read data
      ...
      """
      self.sl.l.acquire()
      try:
         bytes = u2i(
            _pigpio_command(self.sl, _PI_CMD_FR, handle, count))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def file_write(self, handle, data):
      """
      Writes the data bytes to the file associated with handle.

      handle:= >=0 (as returned by a prior call to [*file_open*]).
        data:= the bytes to write.

      ...
      pi.file_write(h1, b'\\x02\\x03\\x04')

      pi.file_write(h2, b'help')

      pi.file_write(h2, "hello")

      pi.file_write(h1, [2, 3, 4])
      ...
      """
      # I p1 handle
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_FW, handle, 0, len(data), [data]))

   def file_seek(self, handle, seek_offset, seek_from):
      """
      Seeks to a position relative to the start, current position,
      or end of the file.  Returns the new position.

           handle:= >=0 (as returned by a prior call to [*file_open*]).
      seek_offset:= byte offset.
        seek_from:= FROM_START, FROM_CURRENT, or FROM_END.

      ...
      new_pos = pi.file_seek(h, 100, pigpio.FROM_START)

      cur_pos = pi.file_seek(h, 0, pigpio.FROM_CURRENT)

      file_size = pi.file_seek(h, 0, pigpio.FROM_END)
      ...
      """
      # I p1 handle
      # I p2 seek_offset
      # I p3 4
      ## extension ##
      # I seek_from
      extents = [struct.pack("I", seek_from)]
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_FS, handle, seek_offset, 4, extents))

   def file_list(self, fpattern):
      """
      Returns a list of files which match a pattern.

      fpattern:= file pattern to match.

      Returns the number of returned bytes if OK, otherwise
      PI_NO_FILE_ACCESS, or PI_NO_FILE_MATCH.

      The pattern must match an entry in /opt/pigpio/access.  The
      pattern may contain wildcards.  See [*file_open*].

      NOTE

      The returned value is not the number of files, it is the number
      of bytes in the buffer.  The file names are separated by newline
      characters.

      ...
      #!/usr/bin/env python

      import pigpio

      pi = pigpio.pi()

      if not pi.connected:
         exit()

      # Assumes /opt/pigpio/access contains the following line:
      # /ram/*.c r

      c, d = pi.file_list("/ram/p*.c")
      if c > 0:
         print(d)

      pi.stop()
      ...
      """
      # I p1 60000
      # I p2 0
      # I p3 len
      ## extension ##
      # s len data bytes

      self.sl.l.acquire()
      try:
         bytes = u2i(_pigpio_command_ext(
            self.sl, _PI_CMD_FL, 60000, 0, len(fpattern), [fpattern]))
         if bytes > 0:
            data = self._rxbuf(bytes)
         else:
            data = ""
      finally:
         self.sl.l.release()
      return bytes, data

   def shell(self, shellscr, pstring=""):
      """
      This function uses the system call to execute a shell script
      with the given string as its parameter.

      shellscr:= the name of the script, only alphanumerics,
                    '-' and '_' are allowed in the name
      pstring := the parameter string to pass to the script

      The exit status of the system call is returned if OK,
      otherwise PI_BAD_SHELL_STATUS.

      [*shellscr*] must exist in /opt/pigpio/cgi and must be executable.

      The returned exit status is normally 256 times that set by
      the shell script exit function.  If the script can't be
      found 32512 will be returned.

      The following table gives some example returned statuses:

      Script exit status @ Returned system call status
      1                  @ 256
      5                  @ 1280
      10                 @ 2560
      200                @ 51200
      script not found   @ 32512

      ...
      // pass two parameters, hello and world
      status = pi.shell("scr1", "hello world");

      // pass three parameters, hello, string with spaces, and world
      status = pi.shell("scr1", "hello 'string with spaces' world");

      // pass one parameter, hello string with spaces world
      status = pi.shell("scr1", "\\"hello string with spaces world\\"");
      ...
      """
      # I p1 len(shellscr)
      # I p2 0
      # I p3 len(shellscr)+len(pstring)+1
      ## extension ##
      # s len data bytes

      ls = len(shellscr)
      lp = len(pstring)
      return _u2i(_pigpio_command_ext(
         self.sl, _PI_CMD_SHELL, ls, 0, ls+lp+1, [shellscr+'\x00'+pstring]))


   def callback(self, user_gpio, edge=RISING_EDGE, func=None):
      """
      Calls a user supplied function (a callback) whenever the
      specified GPIO edge is detected.

      user_gpio:= 0-31.
           edge:= EITHER_EDGE, RISING_EDGE (default), or FALLING_EDGE.
           func:= user supplied callback function.

      The user supplied callback receives three parameters, the GPIO,
      the level, and the tick.

      . .
      Parameter   Value    Meaning

      GPIO        0-31     The GPIO which has changed state

      level       0-2      0 = change to low (a falling edge)
                           1 = change to high (a rising edge)
                           2 = no level change (a watchdog timeout)

      tick        32 bit   The number of microseconds since boot
                           WARNING: this wraps around from
                           4294967295 to 0 roughly every 72 minutes
      . .

      If a user callback is not specified a default tally callback is
      provided which simply counts edges.  The count may be retrieved
      by calling the tally function.  The count may be reset to zero
      by calling the reset_tally function.

      The callback may be cancelled by calling the cancel function.

      A GPIO may have multiple callbacks (although I can't think of
      a reason to do so).

      ...
      def cbf(gpio, level, tick):
         print(gpio, level, tick)

      cb1 = pi.callback(22, pigpio.EITHER_EDGE, cbf)

      cb2 = pi.callback(4, pigpio.EITHER_EDGE)

      cb3 = pi.callback(17)

      print(cb3.tally())

      cb3.reset_tally()

      cb1.cancel() # To cancel callback cb1.
      ...
      """
      return _callback(self._notify, user_gpio, edge, func)

   def event_callback(self, event, func=None):
      """
      Calls a user supplied function (a callback) whenever the
      specified event is signalled.

      event:= 0-31.
       func:= user supplied callback function.

      The user supplied callback receives two parameters, the event id,
      and the tick.

      If a user callback is not specified a default tally callback is
      provided which simply counts events.  The count may be retrieved
      by calling the tally function.  The count may be reset to zero
      by calling the reset_tally function.

      The callback may be cancelled by calling the event_cancel function.

      An event may have multiple callbacks (although I can't think of
      a reason to do so).

      ...
      def cbf(event, tick):
         print(event, tick)

      cb1 = pi.event_callback(22, cbf)

      cb2 = pi.event_callback(4)

      print(cb2.tally())

      cb2.reset_tally()

      cb1.event_cancel() # To cancel callback cb1.
      ...
      """

      return _event(self._notify, event, func)

   def wait_for_edge(self, user_gpio, edge=RISING_EDGE, wait_timeout=60.0):
      """
      Wait for an edge event on a GPIO.

         user_gpio:= 0-31.
              edge:= EITHER_EDGE, RISING_EDGE (default), or
                     FALLING_EDGE.
      wait_timeout:= >=0.0 (default 60.0).

      The function returns when the edge is detected or after
      the number of seconds specified by timeout has expired.

      Do not use this function for precise timing purposes,
      the edge is only checked 20 times a second. Whenever
      you need to know the accurate time of GPIO events use
      a [*callback*] function.

      The function returns True if the edge is detected,
      otherwise False.

      ...
      if pi.wait_for_edge(23):
         print("Rising edge detected")
      else:
         print("wait for edge timed out")

      if pi.wait_for_edge(23, pigpio.FALLING_EDGE, 5.0):
         print("Falling edge detected")
      else:
         print("wait for falling edge timed out")
      ...
      """
      a = _wait_for_edge(self._notify, user_gpio, edge, wait_timeout)
      return a.trigger

   def wait_for_event(self, event, wait_timeout=60.0):
      """
      Wait for an event.

             event:= 0-31.
      wait_timeout:= >=0.0 (default 60.0).

      The function returns when the event is signalled or after
      the number of seconds specified by timeout has expired.

      The function returns True if the event is detected,
      otherwise False.

      ...
      if pi.wait_for_event(23):
         print("event detected")
      else:
         print("wait for event timed out")
      ...
      """
      a = _wait_for_event(self._notify, event, wait_timeout)
      return a.trigger

   def __init__(self,
                host = os.getenv("PIGPIO_ADDR", 'localhost'),
                port = os.getenv("PIGPIO_PORT", 8888)):
      """
      Grants access to a Pi's GPIO.

      host:= the host name of the Pi on which the pigpio daemon is
             running.  The default is localhost unless overridden by
             the PIGPIO_ADDR environment variable.
       
      port:= the port number on which the pigpio daemon is listening.
             The default is 8888 unless overridden by the PIGPIO_PORT
             environment variable.  The pigpio daemon must have been
             started with the same port number.

      This connects to the pigpio daemon and reserves resources
      to be used for sending commands and receiving notifications.

      An instance attribute [*connected*] may be used to check the
      success of the connection.  If the connection is established
      successfully [*connected*] will be True, otherwise False.

      ...
      pi = pigio.pi()              # use defaults
      pi = pigpio.pi('mypi')       # specify host, default port
      pi = pigpio.pi('mypi', 7777) # specify host and port

      pi = pigpio.pi()             # exit script if no connection
      if not pi.connected:
         exit()
      ...
      """
      self.connected = True

      self.sl = _socklock()
      self._notify  = None

      port = int(port)

      if host == '':
         host = "localhost"

      self._host = host
      self._port = port

      try:
         self.sl.s = socket.create_connection((host, port), None)

         # Disable the Nagle algorithm.
         self.sl.s.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)

         self._notify = _callback_thread(self.sl, host, port)

      except socket.error:
         exception = 1

      except struct.error:
         exception = 2

      except error:
         exception = 3

      else:
         exception = 0
         atexit.register(self.stop)

      if exception != 0:

         self.connected = False

         if self.sl.s is not None:
            self.sl.s = None

         s = "Can't connect to pigpio at {}({})".format(host, str(port))

         print(_except_a.format(s))
         if exception == 1:
             print(_except_1)
         elif exception == 2:
             print(_except_2)
         else:
             print(_except_3)
         print(_except_z)

   def stop(self):
      """Release pigpio resources.

      ...
      pi.stop()
      ...
      """

      self.connected = False

      if self._notify is not None:
         self._notify.stop()
         self._notify = None

      if self.sl.s is not None:
         self.sl.s.close()
         self.sl.s = None

def xref():
   """
   active: 0-1000000
   The number of microseconds level changes are reported for once
   a noise filter has been triggered (by [*steady*] microseconds of
   a stable level).


   arg1:
   An unsigned argument passed to a user customised function.  Its
   meaning is defined by the customiser.

   arg2:
   An unsigned argument passed to a user customised function.  Its
   meaning is defined by the customiser.

   argx:
   An array of bytes passed to a user customised function.
   Its meaning and content is defined by the customiser.

   baud:
   The speed of serial communication (I2C, SPI, serial link, waves)
   in bits per second.

   bb_bits: 1-32
   The number of data bits to be used when adding serial data to a
   waveform.

   bb_stop: 2-8
   The number of (half) stop bits to be used when adding serial data
   to a waveform.

   bit: 0-1
   A value of 0 or 1.

   bits: 32 bit number
   A mask used to select GPIO to be operated on.  If bit n is set
   then GPIO n is selected.  A convenient way of setting bit n is to
   bit or in the value (1<<n).

   To select GPIO 1, 7, 23

   bits = (1<<1) | (1<<7) | (1<<23)

   bsc_control:

   . .
   22 21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
    a  a  a  a  a  a  a  -  - IT HC TF IR RE TE BK EC ES PL PH I2 SP EN
   . .

   aaaaaaa defines the I2C slave address (only relevant in I2C mode)

   Bits 0-13 are copied unchanged to the BSC CR register.  See
   pages 163-165 of the Broadcom peripherals document.

   byte_val: 0-255
   A whole number.

   clkfreq: 4689-250M
   The hardware clock frequency.

   connected:
   True if a connection was established, False otherwise.

   count:
   The number of bytes of data to be transferred.

   CS:
   The GPIO used for the slave select signal when bit banging SPI.

   data:
   Data to be transmitted, a series of bytes.

   delay: >=1
   The length of a pulse in microseconds.

   dutycycle: 0-range_
   A number between 0 and range_.

   The dutycycle sets the proportion of time on versus time off during each
   PWM cycle.

   Dutycycle     @ On time
   0             @ Off
   range_ * 0.25 @ 25% On
   range_ * 0.50 @ 50% On
   range_ * 0.75 @ 75% On
   range_        @ Fully On

   edge: 0-2

   . .
   EITHER_EDGE = 2 
   FALLING_EDGE = 1 
   RISING_EDGE = 0
   . .

   errnum: <0

   . .
   PI_BAD_USER_GPIO = -2
   PI_BAD_GPIO = -3
   PI_BAD_MODE = -4
   PI_BAD_LEVEL = -5
   PI_BAD_PUD = -6
   PI_BAD_PULSEWIDTH = -7
   PI_BAD_DUTYCYCLE = -8
   PI_BAD_WDOG_TIMEOUT = -15
   PI_BAD_DUTYRANGE = -21
   PI_NO_HANDLE = -24
   PI_BAD_HANDLE = -25
   PI_BAD_WAVE_BAUD = -35
   PI_TOO_MANY_PULSES = -36
   PI_TOO_MANY_CHARS = -37
   PI_NOT_SERIAL_GPIO = -38
   PI_NOT_PERMITTED = -41
   PI_SOME_PERMITTED = -42
   PI_BAD_WVSC_COMMND = -43
   PI_BAD_WVSM_COMMND = -44
   PI_BAD_WVSP_COMMND = -45
   PI_BAD_PULSELEN = -46
   PI_BAD_SCRIPT = -47
   PI_BAD_SCRIPT_ID = -48
   PI_BAD_SER_OFFSET = -49
   PI_GPIO_IN_USE = -50
   PI_BAD_SERIAL_COUNT = -51
   PI_BAD_PARAM_NUM = -52
   PI_DUP_TAG = -53
   PI_TOO_MANY_TAGS = -54
   PI_BAD_SCRIPT_CMD = -55
   PI_BAD_VAR_NUM = -56
   PI_NO_SCRIPT_ROOM = -57
   PI_NO_MEMORY = -58
   PI_SOCK_READ_FAILED = -59
   PI_SOCK_WRIT_FAILED = -60
   PI_TOO_MANY_PARAM = -61
   PI_SCRIPT_NOT_READY = -62
   PI_BAD_TAG = -63
   PI_BAD_MICS_DELAY = -64
   PI_BAD_MILS_DELAY = -65
   PI_BAD_WAVE_ID = -66
   PI_TOO_MANY_CBS = -67
   PI_TOO_MANY_OOL = -68
   PI_EMPTY_WAVEFORM = -69
   PI_NO_WAVEFORM_ID = -70
   PI_I2C_OPEN_FAILED = -71
   PI_SER_OPEN_FAILED = -72
   PI_SPI_OPEN_FAILED = -73
   PI_BAD_I2C_BUS = -74
   PI_BAD_I2C_ADDR = -75
   PI_BAD_SPI_CHANNEL = -76
   PI_BAD_FLAGS = -77
   PI_BAD_SPI_SPEED = -78
   PI_BAD_SER_DEVICE = -79
   PI_BAD_SER_SPEED = -80
   PI_BAD_PARAM = -81
   PI_I2C_WRITE_FAILED = -82
   PI_I2C_READ_FAILED = -83
   PI_BAD_SPI_COUNT = -84
   PI_SER_WRITE_FAILED = -85
   PI_SER_READ_FAILED = -86
   PI_SER_READ_NO_DATA = -87
   PI_UNKNOWN_COMMAND = -88
   PI_SPI_XFER_FAILED = -89
   PI_NO_AUX_SPI = -91
   PI_NOT_PWM_GPIO = -92
   PI_NOT_SERVO_GPIO = -93
   PI_NOT_HCLK_GPIO = -94
   PI_NOT_HPWM_GPIO = -95
   PI_BAD_HPWM_FREQ = -96
   PI_BAD_HPWM_DUTY = -97
   PI_BAD_HCLK_FREQ = -98
   PI_BAD_HCLK_PASS = -99
   PI_HPWM_ILLEGAL = -100
   PI_BAD_DATABITS = -101
   PI_BAD_STOPBITS = -102
   PI_MSG_TOOBIG = -103
   PI_BAD_MALLOC_MODE = -104
   PI_BAD_SMBUS_CMD = -107
   PI_NOT_I2C_GPIO = -108
   PI_BAD_I2C_WLEN = -109
   PI_BAD_I2C_RLEN = -110
   PI_BAD_I2C_CMD = -111
   PI_BAD_I2C_BAUD = -112
   PI_CHAIN_LOOP_CNT = -113
   PI_BAD_CHAIN_LOOP = -114
   PI_CHAIN_COUNTER = -115
   PI_BAD_CHAIN_CMD = -116
   PI_BAD_CHAIN_DELAY = -117
   PI_CHAIN_NESTING = -118
   PI_CHAIN_TOO_BIG = -119
   PI_DEPRECATED = -120
   PI_BAD_SER_INVERT = -121
   PI_BAD_FOREVER = -124
   PI_BAD_FILTER = -125
   PI_BAD_PAD = -126
   PI_BAD_STRENGTH = -127
   PI_FIL_OPEN_FAILED = -128
   PI_BAD_FILE_MODE = -129
   PI_BAD_FILE_FLAG = -130
   PI_BAD_FILE_READ = -131
   PI_BAD_FILE_WRITE = -132
   PI_FILE_NOT_ROPEN = -133
   PI_FILE_NOT_WOPEN = -134
   PI_BAD_FILE_SEEK = -135
   PI_NO_FILE_MATCH = -136
   PI_NO_FILE_ACCESS = -137
   PI_FILE_IS_A_DIR = -138
   PI_BAD_SHELL_STATUS = -139
   PI_BAD_SCRIPT_NAME = -140
   PI_BAD_SPI_BAUD = -141
   PI_NOT_SPI_GPIO = -142
   PI_BAD_EVENT_ID = -143 
   . .

   event:0-31
   An event is a signal used to inform one or more consumers
   to start an action.

   file_mode:
   The mode may have the following values

   . .
   FILE_READ   1
   FILE_WRITE  2
   FILE_RW     3
   . .

   The following values can be or'd into the file open mode

   . .
   FILE_APPEND 4
   FILE_CREATE 8
   FILE_TRUNC  16
   . .

   file_name:
   A full file path.  To be accessible the path must match
   an entry in /opt/pigpio/access.

   fpattern:
   A file path which may contain wildcards.  To be accessible the path
   must match an entry in /opt/pigpio/access.

   frequency: 0-40000
   Defines the frequency to be used for PWM on a GPIO.
   The closest permitted frequency will be used.

   func:
   A user supplied callback function.

   gpio: 0-53
   A Broadcom numbered GPIO.  All the user GPIO are in the range 0-31.

   There  are 54 General Purpose Input Outputs (GPIO) named GPIO0
   through GPIO53.

   They are split into two  banks.   Bank  1  consists  of  GPIO0
   through GPIO31.  Bank 2 consists of GPIO32 through GPIO53.

   All the GPIO which are safe for the user to read and write are in
   bank 1.  Not all GPIO in bank 1 are safe though.  Type 1 boards
   have 17  safe GPIO.  Type 2 boards have 21.  Type 3 boards have 26.

   See [*get_hardware_revision*].

   The user GPIO are marked with an X in the following table

   . .
             0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
   Type 1    X  X  -  -  X  -  -  X  X  X  X  X  -  -  X  X
   Type 2    -  -  X  X  X  -  -  X  X  X  X  X  -  -  X  X
   Type 3          X  X  X  X  X  X  X  X  X  X  X  X  X  X

            16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
   Type 1    -  X  X  -  -  X  X  X  X  X  -  -  -  -  -  -
   Type 2    -  X  X  -  -  -  X  X  X  X  -  X  X  X  X  X
   Type 3    X  X  X  X  X  X  X  X  X  X  X  X  -  -  -  -
   . .

   gpio_off:
   A mask used to select GPIO to be operated on.  See [*bits*].

   This mask selects the GPIO to be switched off at the start
   of a pulse.

   gpio_on:
   A mask used to select GPIO to be operated on.  See [*bits*].

   This mask selects the GPIO to be switched on at the start
   of a pulse.

   handle: >=0
   A number referencing an object opened by one of the following

   [*file_open*] 
   [*i2c_open*] 
   [*notify_open*] 
   [*serial_open*] 
   [*spi_open*]

   host:
   The name or IP address of the Pi running the pigpio daemon.

   i2c_*:
   One of the i2c_ functions.

   i2c_address: 0-0x7F
   The address of a device on the I2C bus.

   i2c_bus: >=0
   An I2C bus number.

   i2c_flags: 0
   No I2C flags are currently defined.

   invert: 0-1
   A flag used to set normal or inverted bit bang serial data
   level logic.

   level: 0-1 (2)

   . .
   CLEAR = 0 
   HIGH = 1 
   LOW = 0 
   OFF = 0 
   ON = 1 
   SET = 1 
   TIMEOUT = 2 # only returned for a watchdog timeout
   . .

   MISO:
   The GPIO used for the MISO signal when bit banging SPI.

   mode:

   1.The operational mode of a GPIO, normally INPUT or OUTPUT.

   . .
   ALT0 = 4 
   ALT1 = 5 
   ALT2 = 6 
   ALT3 = 7 
   ALT4 = 3 
   ALT5 = 2 
   INPUT = 0 
   OUTPUT = 1
   . .

   2. The mode of waveform transmission.

   . .
   WAVE_MODE_ONE_SHOT = 0 
   WAVE_MODE_REPEAT = 1 
   WAVE_MODE_ONE_SHOT_SYNC = 2 
   WAVE_MODE_REPEAT_SYNC = 3
   . .

   MOSI:
   The GPIO used for the MOSI signal when bit banging SPI.

   offset: >=0
   The offset wave data starts from the beginning of the waveform
   being currently defined.

   pad: 0-2
   A set of GPIO which share common drivers.

   Pad @  GPIO
   0   @  0-27
   1   @  28-45
   2   @  46-53

   pad_strength: 1-16
   The mA which may be drawn from each GPIO whilst still guaranteeing the
   high and low levels.

   params: 32 bit number
   When scripts are started they can receive up to 10 parameters
   to define their operation.

   port: 
   The port used by the pigpio daemon, defaults to 8888.

   pstring:
   The string to be passed to a [*shell*] script to be executed.

   pud: 0-2
   . .
   PUD_DOWN = 1 
   PUD_OFF = 0 
   PUD_UP = 2 
   . .

   pulse_len: 1-100
   The length of the trigger pulse in microseconds.

   pulses:
   A list of class pulse objects defining the characteristics of a
   waveform.

   pulsewidth:
   The servo pulsewidth in microseconds.  0 switches pulses off.

   PWMduty: 0-1000000 (1M)
   The hardware PWM dutycycle.

   PWMfreq: 1-125000000 (125M)
   The hardware PWM frequency.

   range_: 25-40000
   Defines the limits for the [*dutycycle*] parameter.

   range_ defaults to 255.

   reg: 0-255
   An I2C device register.  The usable registers depend on the
   actual device.

   retMax: >=0
   The maximum number of bytes a user customised function
   should return, default 8192.

   SCL:
   The user GPIO to use for the clock when bit banging I2C.

   SCLK::
   The GPIO used for the SCLK signal when bit banging SPI.

   script:
   The text of a script to store on the pigpio daemon.

   script_id: >=0
   A number referencing a script created by [*store_script*].

   SDA:
   The user GPIO to use for data when bit banging I2C.

   seek_from: 0-2
   Direction to seek for [*file_seek*].

   . .
   FROM_START=0 
   FROM_CURRENT=1 
   FROM_END=2 
   . .

   seek_offset:
   The number of bytes to move forward (positive) or backwards
   (negative) from the seek position (start, current, or end of file).

   ser_flags: 32 bit
   No serial flags are currently defined.

   serial_*:
   One of the serial_ functions.

   shellscr:
   The name of a shell script.  The script must exist
   in /opt/pigpio/cgi and must be executable.

   spi_*:
   One of the spi_ functions.

   spi_channel: 0-2
   A SPI channel.

   spi_flags: 32 bit
   See [*spi_open*].

   steady: 0-300000

   The number of microseconds level changes must be stable for
   before reporting the level changed ([*set_glitch_filter*])
   or triggering the active part of a noise filter
   ([*set_noise_filter*]).

   t1:
   A tick (earlier).

   t2:
   A tick (later).

   tty:
   A Pi serial tty device, e.g. /dev/ttyAMA0, /dev/ttyUSB0

   uint32:
   An unsigned 32 bit number.

   user_gpio: 0-31
   A Broadcom numbered GPIO.

   All the user GPIO are in the range 0-31.

   Not all the GPIO within this range are usable, some are reserved
   for system use.

   See [*gpio*].

   wait_timeout: 0.0 -
   The number of seconds to wait in [*wait_for_edge*] before timing out.

   wave_add_*:
   One of the following

   [*wave_add_new*] 
   [*wave_add_generic*] 
   [*wave_add_serial*]

   wave_id: >=0
   A number referencing a wave created by [*wave_create*].

   wave_send_*:
   One of the following

   [*wave_send_once*] 
   [*wave_send_repeat*]

   wdog_timeout: 0-60000
   Defines a GPIO watchdog timeout in milliseconds.  If no level
   change is detected on the GPIO for timeout millisecond a watchdog
   timeout report is issued (with level TIMEOUT).

   word_val: 0-65535
   A whole number.
   """
   pass