pi-spi

pi-spi

Simple asyncronous node.js SPI library for Raspberry Pi (and likely other embedded Linux platforms that provide /dev/spidevN.N).

Example

npm install pi-pi

var SPI = require('pi-spi');

var spi = SPI.initialize("/dev/spidev0.0"),
    test = Buffer("Hello, World!");

// reads and writes simultaneously
spi.transfer(test, test.length, function (e,d) {
    if (e) console.error(e);
    else console.log("Got \""+d.toString()+"\" back.");
    
    if (test.toString() === d.toString()) {
        console.log(msg);
    } else {
        // NOTE: this will likely happen unless MISO is jumpered to MOSI
        console.warn(msg);
        process.exit(-2);
    }
});

Probably requires running node under sudo for SPI permissions, unless you've used Wiring Pi's gpio utility or otherwise adjusted device permissions.

API

spi = SPI.initialize(device)

device will usually be "/dev/spidev0.0" or "/dev/spidev0.0". You will first need to enable the spi-bcm2708 kernel module e.g. these instructions or similar for your platform. As mentioned above, by default this device requires root permissions and so you'll either need to change this or run your script with according privilege.

spi.clockSpeed([speed])

Sets (or gets, if no argument provided) the clock speed in Hz. Defaults to 4e6, i.e. 4MHz. The Pi only supports powers of 2 speeds and faster speeds might get derated a bit.

spi.dataMode([mode])

Sets (or gets, if no argument provided) the "data mode" (clock phase and polarity) to e.g. SPI.mode.CPHA | SPI.mode.CPOL. Default is no flags.

spi.bitOrder([order])

Sets (or gets, if no argument provided) the bit ordering. Default is SPI.order.MSB_FIRST or you can set SPI.order.LSB_FIRST.

Note that this is bit ordering, not bytes — byte ordering is up to your application.

spi.transfer(outbuffer, incount, cb)

Transfers data for the longer of outbuffer.length or incount bytes. If successfully, the second parameter to your callback will be a buffer of length incount.

spi.read(incount, cb)

Collects incount bytes while writing as many \0 out.

spi.write(outbuffer, cb)

Writes outbuffer, ignoring response bytes.

Note that if there was an error opening the device, the transfer/read/write calls will fail each time called. I may revise the initialize method so to allow you to handle the error better.

Compatibility Note

This library is subject to change as it is intended for compatibility with $somethingElse.

TBD: more details when public

License

Copyright © 2013, Nathan Vander Wilt. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those of the authors and should not be interpreted as representing official policies, either expressed or implied, of the FreeBSD Project.