[![Hackage](https://img.shields.io/hackage/v/wiringPi.svg)](https://hackage.haskell.org/package/wiringPi)

This is a Haskell binding to the [wiringPi library][1], which allows
you to interface with the [GPIO][4] pins on the [Raspberry Pi][2].
Unlike some other solutions for using the Raspberry Pi's GPIO pins,
wiringPi provides access to more advanced features, such as enabling
the internal pull-up or pull-down resistors.

## Usage

To use this library, you must either run as root, or set the
`WIRINGPI_GPIOMEM` environment variable.  (Set it to anything; the
value does not matter.)  However, [PWM][7] will not work if
`WIRINGPI_GPIOMEM` is set.

This library will only build on the Raspberry Pi.  Before building
this library, you must install the "wiringPi" C library on your
Raspberry Pi, like this:

    sudo apt-get install wiringpi

Tested on a Raspberry Pi Model B, with [Raspbian Jessie Lite][3],
using the system-provided Haskell compiler.  (GHC 7.6.3.)

## Pin Numbering

WiringPi allows each pin to be identified by one of three names.  A
pin can be identified by its physical pin number, by its Broadcom GPIO
number (this is the one most commonly used in the Raspberry Pi
community), or by its wiringPi pin number.  The `Pin` type has three
constructors (`Wpi`, `Gpio`, and `Phys`), allowing you to call a pin
by any of its three names.  These names are synonymous and
interchangeable.

The following diagram illustrates the three names of each pin, and
also identifies which pins can be placed in `PWM_OUTPUT` mode or
[`GPIO_CLOCK`][8] mode.

![Pinout](https://raw.githubusercontent.com/ppelleti/hs-wiringPi/master/pin-diagram.png)

Similar diagrams are available on [the wiringPi site][5] or on
[pinout.xyz][6].

One additional wrinkle is that some very early Raspberry Pis use
different Broadcom GPIO numbers for a few of the pins.  WiringPi
automatically takes this into account, but it means that equality for
`Pin` actually depends on which board revision you have.

## Licensing

This Haskell binding is licensed under the 3-clause BSD license, and
the examples in the `examples` directory are in the public domain.
However, be aware that the wiringPi C library itself is licensed under
the LGPLv3+.

## Examples

There are several examples in the `examples` directory.  You can run
each example by wiring up a circuit on a breadboard as specified by
the comments in the example.  Or, for something more permanent and
professional-looking, you can use the
[hs-wiringPi test board](https://github.com/ppelleti/hs-wiringPi-test-board).
The hs-wiringPi test board can be used with all of the examples,
except for `wpi-fishdish`, which requires the
[Fish Dish](https://www.pi-supply.com/product/fish-dish-raspberry-pi-led-buzzer-board/)
board instead.

[1]: http://wiringpi.com/
[2]: https://www.raspberrypi.org/
[3]: https://www.raspberrypi.org/downloads/raspbian/
[4]: https://en.wikipedia.org/wiki/General-purpose_input/output
[5]: http://wiringpi.com/pins/
[6]: https://pinout.xyz/pinout/wiringpi
[7]: https://en.wikipedia.org/wiki/Pulse-width_modulation
[8]: https://pinout.xyz/pinout/gpclk