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+# pigpio
+pigpio is a C library for the Raspberry which allows control of the
+general purpose input outputs (gpios).
+
+Features
+
+    sampling and time-stamping of gpios 0-31 between 100,000 and 1,000,000 times per second.
+
+    provision of PWM on any number of the user gpios simultaneously.
+
+    provision of servo pulses on any number of the user gpios simultaneously.
+
+    callbacks when any of gpios 0-31 change state (callbacks receive the time of the event
+    accurate to a few microseconds).
+
+    notifications via pipe when any of gpios 0-31 change state.
+
+    callbacks at timed intervals.
+
+    reading/writing all of the gpios 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.
+
+    the construction of arbitrary waveforms to give precise timing of output gpio
+    level changes (accurate to a few microseconds).
+
+    software serial links using any user gpio.
+
+    rudimentary permission control through the socket and pipe interfaces so users
+    can be prevented from "updating" inappropriate gpios.
+
+    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 pigs command line utility.
+
+    the pig2vcd utility which converts notifications into the value change dump (VCD)
+    format (useful for viewing digital waveforms with GTKWave).
+
+gpios
+
+ALL gpios are identified by their Broadcom number.  See elinux.org
+
+There are 54 gpios in total, arranged in two banks.
+
+Bank 1 contains gpios 0-31.  Bank 2 contains gpios 32-54.
+
+A user should only manipulate gpios 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 gpios 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 gpios 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 gpios 2-27 (0 and 1 are reserved).
+
+It is safe to read all the gpios. 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.