chickadee » raspberry-pi-gpio

RaspberryPI GPIO library

This egg provides an interface to the RaspberryPi GPIO pins for CHICKEN Scheme.

Installation / Dependencies

You'll need to install Wiring Pi before using this library. The Wiring Pi documentation may help you understand some of these functions in more detail.


(use raspberry-pi-gpio)


;; digital read / write

(pin-mode 1 'output)

(digital-write 1 HIGH)
(digital-write 1 LOW)

(printf "Pin 1 is: ~S~n" (digital-read 1))

;; using interrupts to respond to events

(set-edge 7 'falling)
(set-edge 8 'both)

(define (loop)
  (receive (pin value intsec intnsec) (receive-gpio-event)
    (printf "Interrupt on pin ~S, interrupt time ~S.~S, value: ~S, value now: ~S ~n"
            pin intsec intnsec value (digital-read pin))



One of the setup functions must be called at the start of your program, or your program will fail to work correctly.

(setup-gpio) procedure

Use the Broadcom GPIO pin numbers when referencing pins.

(setup-virtual) procedure

Use the wiringPi pin numbering scheme. This is a simplified numbering scheme which provides a mapping from virtual pin numbers 0 through 16 to the real underlying Broadcom GPIO pin numbers. See the [Wiring Pi documentation]( for more info.

(setup-physical) procedure

Use the physical pin numbers *on the P1 connector only*.

(setup-system) procedure

Use the /sys/class/gpio interface rather than accessing the hardware directly. This can be called as a non-root user provided the GPIO pins have been exported before-hand using the gpio program.

(board-rev) procedure

Returns the board revision (1 or 2).

(pin-mode pin mode) procedure

Sets the pin to the given mode. Mode is one of the following symbols: `input`, `output`, `pwm-output`, `gpio-clock`.

(pull-up-dn-control pin pud) procedure

This sets the pull-up or pull-down resistor mode on the given pin, which should be set as an input. Pud should be one of the following symbols: `off`, `up`, `down`.

(pwm-write pin value) procedure

Writes the value to the PWM register for the given pin. The Raspberry Pi has one on-board PWM pin, pin 1 (BMC\_GPIO 18, Phys 12) and the range is 0-1024. Other PWM devices may have other PWM ranges.

This function is not able to control the Pi’s on-board PWM when in Sys mode.

(digital-write pin value) procedure

Writes the value HIGH or LOW (1 or 0) to the given pin which must have been previously set as an output.

(digital-write/time pin value) procedure

Writes the value HIGH or LOW (1 or 0) to the given pin which must have been previously set as an output.

Returns two values, seconds and nanoseconds since process- or machine startup when the pin value was changed.

(digital-read pin) procedure

This function returns the value read at the given pin. It will be HIGH or LOW (1 or 0) depending on the logic level at the pin.

(analog-write pin value) procedure

This writes the given value to the supplied analog pin.

(analog-read pin) procedure

This returns the value read on the supplied analog input pin.

(set-edge pin edge) procedure

Sets up an interrupt handler for the pin and given edge using wiringPiISR. Use this to hook up events for use with `recieve-gpio-event`.

Type should be one of the following symbols: `falling`, `rising`, `both`, `setup`. If `setup` is used then no initialisation of the pin will happen – it’s assumed that you have already setup the pin elsewhere (e.g. with the gpio program).

(receive-gpio-event) procedure

Blocks until a GPIO interrupt occurs on a pin that had set-edge called on it.

Returns four values the pin number that caused the interrupt, the value read from the pin in the interrupt routine, the number of seconds and nanoseconds representing the time when the interrupt routine was executed.

(current-time-raw) procedure

Returns two values the number of seconds and nanosecons since process- or machine startup.

Uses Linux' clock_gettime to read CLOCK_MONOTONIC_RAW, i.e. the result value is not effected by adjustments from NTP etc. and therefore suited to measure physical time deltas.

HIGH constant

The HIGH value (1) exported by wiringPi.

LOW constant

The LOW value (0) exported by wiringPi.

Source code / Issues

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