pigpio/README.md

# pigpio

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

## 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).

## Example programs

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

## GPIO

ALL GPIO are identified by their Broadcom number.  See 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.