node-rpio

This is a super-fast nodejs addon which wraps around Mike McCauley's bcm2835 library to allow mmap access via /dev/mem to the GPIO pins.

Most other GPIO modules use the slower /sys file system interface. You should find this module significantly faster than the alternatives. The only drawback is that root access is required to open /dev/mem.

This module also includes support for SPI.

Install

Easily install the latest via npm:

$ npm install rpio

API

Requiring the addon initializes the bcm2835 driver ready to accept commands.

var rpio = require('rpio');

GPIO

By default the gpio layout is used, i.e. GPIOxx, which maps directly to the underlying pin identifiers used by the bcm2835 chip. If you prefer, you can refer to pins by their physical header location instead.

rpio.setMode('physical');  /* Use the physical P1-P26/P40 layout */
rpio.setMode('gpio');      /* The default GPIOxx numbering system */

Before reading from / writing to a pin you need to configure it as read-only or read-write.

rpio.setInput(17);         /* Configure GPIO17 as read-only */
rpio.setOutput(18);        /* Configure GPIO18 as read-write */

Now you can read or write values with .read() and .write(). The two rpio.LOW and rpio.HIGH constants are provided if you prefer to avoid magic numbers.

/* Read value of GPIO17 */
console.log('GPIO17 is set to ' + rpio.read(17));

/* Set GPIO18 high (i.e. write '1' to it) */
rpio.write(18, rpio.HIGH);

/* Set GPIO18 low (i.e. write '0' to it) */
rpio.write(18, rpio.LOW);

SPI

SPI switches pins GPIO7-GPIO11 to a special mode where you can bulk transfer data at high speeds to and from SPI devices, with the controller handling the chip enable, clock and data in/out functions.

Once SPI is enabled, the SPI pins are unavailable for GPIO use until spiEnd() is called.

rpio.spiBegin();           /* Switch GPIO7-GPIO11 to SPI mode */

Choose which of the chip select / chip enable pins to control:

/*
 *  Value | Pin
 *  ------|----
 *    0   | SPI_CE0 (GPIO8)
 *    1   | SPI_CE1 (GPIO7)
 *    2   | Both
 */
rpio.spiChipSelect(0);

Commonly chip enable (CE) pins are active low, and this is the default. If your device's CE pin is active high, use spiSetCSPolarity() to change the polarity.

rpio.spiSetCSPolarity(0, rpio.HIGH);    /* Set CE0 high to activate */

Set the SPI clock speed with spiSetClockDivider(). This is a power-of-two divisor of the base 250MHz rate, defaulting to 0 == 65536 == 3.81kHz.

rpio.spiSetClockDivider(128);   /* Set SPI speed to 1.95MHz */

Set the SPI Data Mode:

/*
 *  Mode | CPOL | CPHA
 *  -----|------|-----
 *    0  |  0   |  0
 *    1  |  0   |  1
 *    2  |  1   |  0
 *    3  |  1   |  1
 */
rpio.spiSetDataMode(0);         /* 0 is the default */

Once everything is set up we can transfer data. Data is sent and received in 8-bit chunks via buffers which should be the same size.

var tx = new Buffer([0x3, 0x0, 0xff, 0xff]);
var rx = new Buffer(tx.length);

rx = rpio.spiTransfer(tx, tx.length);

When you're finished call .spiEnd() to release the pins back to general purpose use.

rpio.spiEnd();

Simple demo

/*
 * Simple demo to flash pin 11 at 100Hz (assuming it's routed to an LED).
 */
var rpio = require('rpio');

// Use physical layout for this one.
rpio.setMode('physical');

// Set physical pin 11 / GPIO17 for write mode
rpio.setOutput(11);

/*
 * Set the pin high every 10ms, and low 5ms after each transition to high.
 */
setInterval(function() {

    rpio.write(11, rpio.HIGH);

    setTimeout(function() {
        rpio.write(11, rpio.LOW);
    }, 5);

}, 10);

Authors/Licenses

Mike McCauley wrote src/bcm2835.{c,h} which are under the GPL.

I wrote the rest, which is under the ISC license unless otherwise specified.