node-libgpiod

Native nodejs bindings for libgpiod

Requirements

• libgpiod (and devel headers)
• nodejs (and devel headers)
• linux (tested on fedora 33 running on raspberry pi model 3 B+ and rasp pi os on zero w)
• c/c++ development tools

Compiling

Just add it as a regular nodejs dependency:

npm i node-libgpiod

node-gyp will do the rest for you

Status

We already are able to read and write pins!

Here goes the sample blink led hello-world.js:

const { version, Chip, Line } = require("node-libgpiod");

const chip = new Chip(0);
const line = new Line(chip, 17); // led on GPIO17
let count = 10;

console.log(version());
line.requestOutputMode();

const blink = () => {
  if(count){
    line.setValue(count-- % 2);
    setTimeout(blink,1000);
  } // else line.release(); 
  // not needed, libgpiod releases resources on process exit  
};

setTimeout(blink,1000);

Another example:

const { version, Chip, Line } = require("node-libgpiod");
const express = require("express");

const app = express();
// avoid chip and line being gc-collected
app.chip = new Chip(0);
app.line = new Line(app.chip, 17); // led on GPIO17

console.log(version());
app.line.requestOutputMode();

app.get("/on", (req,res) => {
  app.line.setValue(1);
  res.send("it's on");
});

app.get("/off", (req,res) => {
  app.line.setValue(0);
  res.send("it's off");
});

app.listen(3000);
console.log("running");

See our testcases for more information

See node-libgpiod-examples for more sample code

known issues

• gpio character device needs special udev rules in order to belong to a special group so non-root users could access it freely

  # /etc/udev/rules.d/85-gpiochip.rules 
  KERNEL=="gpiochip*", SUBSYSTEM=="gpio", MODE="0660", GROUP="wheel"

• libgpiod must be installed in the system correctly with development headers otherwise npm install will fail.
• node will garbage collect Chip and line too early on certain cases. When writing the samples, sometimes the following error kept being thrown:

  /home/sombriks/git/sample-node-libgpiod/index2.js:12
      line.setValue(count-- % 2);
          ^
  
  Error: Unable to set value for this line
      at Timeout.blink [as _onTimeout] (/home/sombriks/git/sample-node-libgpiod/index2.js:12:10)
      at listOnTimeout (internal/timers.js:554:17)
      at processTimers (internal/timers.js:497:7)

  It occurs because main module body was already evaluated and finished while interval/timeout function still active, but has no local reference for Chip or Line instances. Therefore, v8 thinks that those objects can be garbage-collected releasing the underlying resources, giving us the error. To avoid this, make sure your objects will be present on function scope:

  const { version, Chip, Line } = require("node-libgpiod");
  
  const chip = new Chip(0);
  const line = new Line(chip, 17); // led on GPIO17
  let count = 20;
  
  console.log(version());
  line.requestOutputMode();
  
  const blink = function () {
    // avoid early gc
    this.chip = chip
    this.line = line
    if(count){
      line.setValue(count-- % 2);
      setTimeout(blink,500);
    }
  };
  
  setTimeout(blink,500);

Roadmap

• basic read/write
• basic instant read/write
• Chip/Line abstractions
• GPIO monitoring callbacks
• Bulk read/write

All features present on libgpiod eventually will be added to node bindings.

Contributing

This is open source, i am willing to evaluate PR's 😎