node-libgpiod

Native nodejs bindings for libgpiod

Requirements / Dependencies

• libgpiod 1.x (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

How to use into your project

First install libgpiod and node development packages, if not installed yet:

RPM based

# fedora
sudo dnf install libgpiod libgpiod-devel libgpiod-utils nodejs-devel

# openSUSE
sudo zypper in libgpiod libgpiod-devel libgpiod-utils nodejs-devel

DEB based

# debian and its variants
sudo apt install gpiod libgpiod2 libgpiod-dev libnode-dev

Then just add it as a regular nodejs dependency:

npm i node-libgpiod

node-gyp will do the rest for you.

Tested platforms

• raspberry pi model 3 B+ (64 bits, 1GB ram) running fedora
• raspberry pi zero w (32 bits, 512MB ram) running rasp pi os
• LTPPxG2 with sp7021 SoC (32 bits, 512MB ram) running Yocto
• ROCK 5A (64 bits, 2GB ram), running debian
• ROCK 3C (64 bits, 2GB ram), running d

Technically speaking it should work with any modern vanilla kernel and libgpiod 1.x.

What about libgpiod 2.x?

We're still working on libgpiod 2.x

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");

global.chip = new Chip(0);
global.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

• libgpiod 2.x series is around the corner, and its API is incompatible with 1.x the 2.x branch (under development) will handle 2.x while 0.x and 1.x will support libgpiod 1.x series.

• 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.

• inside libgpiod 1.x series there is a set of new flags created on 1.5.x version around 2019 and they where no back ported to previous ones libgpiod releases. Your build might break because of this, we're working on solve this.

• node will garbage collect Chip and Line too early on certain cases. When writing the samples, 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);

  Or, probably it is even better to create you chip and line instances globally:

  global.mychip = new Chip(0);
  global.line1 = new Line(chip, 17);

Roadmap

• basic read/write
• basic instant read/write
• Chip/Line abstractions
• GPIO monitoring callbacks
• Bulk read/write
• Complete API parity with underlying C/C++ library

All features present on libgpiod eventually will be added to node bindings, then the node package will finally enter in 1.x series.

Also see our changelog and project updates for details.

Functionality parity

This is the api parity table:

Description	Scope	C/C++	Node
get line's instant value	Miscellaneous	gpiod_ctxless_get_value	getInstantLineValue
set line's instant value	Miscellaneous	gpiod_ctxless_set_value	setInstantLineValue
get number of lines in a chip	Chip	gpiod_chip_num_lines	getNumberOfLines
get chip name	Chip	gpiod_chip_name	getChipName
get chip label	Chip	gpiod_chip_label	getChipLabel
get line/pin offset number	Line	gpiod_line_offset	getLineOffset
get line/pin name	Line	gpiod_line_name	getLineName
get line/pin value	Line	gpiod_line_get_value	getValue
set line/pin value	Line	gpiod_line_set_value	setValue
get line consumer	Line	gpiod_line_consumer	getLineConsumer
set line for input (read)	Line	gpiod_line_request_input	requestInputMode
set line for input with flags	Line	gpiod_line_request_input_flags	requestInputModeFlags
set line for output (write)	Line	gpiod_line_request_output	requestOutputMode
release the line	Line	gpiod_line_release	release

Other implementations

Those are other notable libgpiod wrapper implementations:

Official C++ binding

• https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/tree/bindings/cxx?h=v1.6.x

Official Python binding

• https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/tree/bindings/python?h=v1.6.x

Golang binding

Rust binding

Contributing

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