pigpio/README.md

# pigpio

pigpio is a C library for the Raspberry which allows control of the
General Purpose Input Outputs (GPIO).

At the moment pigpio on the Pi4B is experimental. I am not sure if the DMA channels
    being used are safe.  The Pi4B defaults are primary channel 7, secondary channel 6.
    If these channels do not work you will have to experiment. You can set the channels
    used by the pigpio daemon by invoking it with the -d and -e options, e.g. 
    <small>sudo pigpiod -d 5 -e 8</small> to specify primary 5, secondary 8.

## Features

* Sampling and time-stamping of GPIO 0-31 between 100,000 and 1,000,000 times per second
* Provision of PWM on any number of the user GPIO simultaneously
* Provision of servo pulses on any number of the user GPIO simultaneously
* Callbacks when any of GPIO 0-31 change state (callbacks receive the time of the event
  accurate to a few microseconds)
* Notifications via pipe when any of GPIO 0-31 change state
* Callbacks at timed intervals
* Reading/writing all of the GPIO in a bank (0-31, 32-53) as a single operation
* Individually setting GPIO modes, reading and writing
* Socket and pipe interfaces for the bulk of the functionality in addition to the
  underlying C library calls
* Construction of arbitrary waveforms to give precise timing of output GPIO
  level changes (accurate to a few microseconds)
* Software serial links, I2C, and SPI using any user GPIO
* Rudimentary permission control through the socket and pipe interfaces so users
  can be prevented from "updating" inappropriate GPIO
* Creating and running scripts on the pigpio daemon

## Interfaces

The library provides a number of control interfaces
* the C function interface,
* the /dev/pigpio pipe interface,
* the socket interface (used by the pigs utility and the Python module).

## Utilities

A number of utility programs are provided:
* the pigpiod daemon,
* the Python module,
* the piscope digital waveform viewer,
* the pigs command line utility,
* the pig2vcd utility which converts notifications into the value change dump (VCD)
  format (useful for viewing digital waveforms with GTKWave).

## Documentation

See http://abyz.me.uk/rpi/pigpio/

## Example programs

See http://abyz.me.uk/rpi/pigpio/examples.html

## GPIO

ALL GPIO are identified by their Broadcom number.  See http://elinux.org.

There are 54 GPIO in total, arranged in two banks.

Bank 1 contains GPIO 0-31.  Bank 2 contains GPIO 32-54.

A user should only manipulate GPIO in bank 1.

There are at least three types of board:
* Type 1
    * 26 pin header (P1)
    * Hardware revision numbers of 2 and 3
    * User GPIO 0-1, 4, 7-11, 14-15, 17-18, 21-25
* Type 2
    * 26 pin header (P1) and an additional 8 pin header (P5)
    * Hardware revision numbers of 4, 5, 6, and 15
    * User GPIO 2-4, 7-11, 14-15, 17-18, 22-25, 27-31
* Type 3
    * 40 pin expansion header (J8)
    * Hardware revision numbers of 16 or greater
    * User GPIO 2-27 (0 and 1 are reserved)

It is safe to read all the GPIO. If you try to write a system GPIO or change
its mode you can crash the Pi or corrupt the data on the SD card.