Getting started

Bonescript is a node.js library for physical computing on embedded Linux, starting with support for BeagleBone.

Information on the language is available at http://nodejs.org.

To get started, try running 'node blinkled.js' on a BeagleBone.

Additional documentation is available at http://beagleboard.org/bonescript.

The concept is to use Arduino-like functions written in JavaScript to simplify learning how to do physical computing tasks under embedded Linux and to further provide support for rapidly creating GUIs for your embedded applications through the use of HTML5/JavaScript web pages.

Installation

Bonescript comes installed on your BeagleBone. If you are looking to update to the latest revision, use 'opkg' to perform the update:

opkg update
opkg install bonescript

Support for other distributions is a work in progress.

Launching applications persistently

To have your applications launch on startup, simply drop them into the /var/lib/cloud9/autorun folder. Moving them out of that folder will kill the processes. You are expected to only drop in already bug-free apps into this folder as there isn't a good way to perform debug on them.

Note on code state

There's still a lot of development going on, so be sure to check back on a frequent basis. Many of the fancier peripherals aren't yet supported except through performing file I/O.

Directory layout

• attic: Stuff not to throw away, but not in a good state
• demo: Examples showing how to use the BoneScript library
• etc: Configuration files to be placed in target distro
• node_modules: Library code
• systemd: Configuration files for systemd to start services
• test: Automated test code

Template

For a Bonescript application, you must currently manually 'require' the bonescript library. Functions are then referenced through the object provided back from require.

I started out trying to provide Arduino-like setup/loop functions, but the idea really isn't a good match for JavaScript. Using JavaScript's native flow works best, but the familiar functions are enough to give you a boost in your physical computing productivity.

Here's an example:

var b = require('bonescript');

b.pinMode('P8_12', b.INPUT);
b.pinMode('P8_13', b.OUTPUT);

setInterval(copyInputToOutput, 100);

function copyInputToOutput() {
    b.digitalRead('P8_12', writeToOutput);
    function writeToOutput(x) {
        b.digitalWrite('P8_13', x.value);
    }
}

The 'P8_12' and 'P8_13' are pin names on the board and the above example would copy the input value at P8_12 to the output P8_13 every 100 ms.

API

When a callback is provided, the functions will behave asynchronously. Without a callback provided, the functions will synchronize and complete before returning.

Digital I/O, Analog I/O, and Advanced I/O

• analogRead(pin, [callback]) -> value
• analogWrite(pin, value, [freq], [callback])
• attachInterrupt(pin, handler, mode, [callback])
• detachInterrupt(pin, [callback])
• digitalRead(pin, [calback]) -> value
• digitalWrite(pin, value, [callback])
• getEeproms([callback]) -> eeproms
• pinMode(pin, direction, [mux], [pullup], [slew], [callback])
• getPinMode(pin, [callback]) -> pinMode
• shiftOut(dataPin, clockPin, bitOrder, val, [callback])

Bits/Bytes, Math, Trigonometry and Random Numbers

• lowByte(value)
• highByte(value)
• bitRead(value, bitnum)
• bitWrite(value, bitnum, bitdata)
• bitSet(value, bitnum)
• bitClear(value, bitnum)
• bit(bitnum)
• min(x, y)
• max(x, y)
• abs(x)
• constrain(x, a, b)
• map(value, fromLow, fromHigh, toLow, toHigh)
• pow(x, y)
• sqrt(x)
• sin(radians)
• cos(radians)
• tan(radians)
• randomSeed(x)
• random([min], max)

Note on performance

This code is totally unoptimized. The list of possible optimizations that run through my head is staggering. The good news is that I think it can all be done without impacting the API, primarily thanks to the introspection capabilities of JavaScript.

Eventually, this is planned to enable real-time usage, directly from JavaScript. The plan is to attact the ability to use this programming environment in real-time on several fronts:

• Enabling multiple loops and analyzing them to determine if they can be off- loaded to a PRU. This will be the primary mechanism for providing real-time servicing of the IOs.
• Providing higher-order services that utilize the standard peripherals for their intended use:
  • Serial drivers for I2C, SPI, UARTs, etc.
  • analogWrite for PWMs using hardware PWMs, timers, kernel GPIO drivers, etc.
• Adding real-time patches to the kernel

The JavaScript language provides some features that I think are really cool for doing embedded programming and node.js does some things to help enable that. The primary one is that the I/O functions are all asynchronous. For embedded systems, this is especially useful for performing low-latency tasks that respond to events in the system. What makes JavaScript so much easier than other languages for doing this is that it keeps the full context around the handler, so you don't have to worry about it.

Short-term issues

• The state of the ARM Linux kernel with regards to handling loading drivers using devicetree is still in a lot of flux. Many of the interfaces Bonescript utilizes are being rewritten and refactored.