node-libgpiod

Appearance

It's all about javascript and wires, baby ​

Assuming all requirements where met and environment setup is done, it's time to do some real work.

Check your hardware ​

use the commands gpiodetect and gpioinfo to get details about the hardware.

Uou need at least two key information:

  • The gpio chip names or numbers.
  • The gpio lines labels or numbers.

On some libraries, you just request a pin and read or write to it.

Although node-libgpiod offers a Pin, it's just a syntax sugar for a line from the first chip.

Create a chip ​

It's pretty simple:

javascript
// const gpio = require('node-libgpiod')
import gpio from 'node-libgpiod'

const chip = new gpio.Chip(0)

// ...

To be sure about the chip namer or number, check available chops with gpiodetect.

create a line ​

Once you have a chip instance, get the line you want to work with:

javascript
import gpio from 'node-libgpiod'

const chip = new gpio.Chip(0)

// const line = new gpio.Line(chip, 20)
const line = chip.getLine(20)

line.requestOutputMode()
line.setValue(1)

// line.requestInputMode()
// let v = line.getValue()
// let v2 = line.value

// ...

// if(line.used)
// if(!line.free)
line.release()

//...

Key features about the line are:

  • You must set the mode before perform any operation on the line.
  • Once you're done with the line, release it. If it goes out of scope, the garbage collector will take care of it, but if it's not collected yet, it will throw an error.

It's up to the SBC docs to document the available lines ​

It is possible to create chips and lines either by their numbers, found using gpiodetect and gpioinfo, but also by their names.

It's common to find line names like GPIO_7, but it will depend on the specific hardware and software combination.

If things get hard and documentation get scarce, you can scan the hardware using libgpiod tools or some scripts to check the hardware:

javascript
// scan.js
// const gpio = require('node-libgpiod')
import gpio from 'node-libgpiod'

for(const chName of gpio.chipNames) {
  const chip = new gpio.Chip(chName)
  for(const n in chip.lineNames) {
    console.log(`chip ${chName} line #${n}: ${chip.lineNames[n]}`)
  }
}