I2c-bus-promised NPM

i2c-bus-promised

Bus and Device classes for i2c-bus, with promised functions.

Installation

npm install --save i2c-bus-promised

Usage

There's two main class exports in this library: Bus and Device.

Bus class wraps original i2c-bus methods and returns them promised, to make more comofrtable to work with them. The calls are queued to avoid blocking calls to the i2c bus. Device class abstracts an i2c device.The class is initialised with two arguments, bus and device address. Internally it will call the reciprocal methods on the bus object with it's address.

// @flow
/* eslint-disable no-console */
import { Bus, Device } from '../src';
import type { AddrType, WordType } from '../src/types';

const main = async () => {
  const bus = new Bus();
  await bus.open();

  // Print bus info
  await Promise.all([
    bus.i2cFuncs().then((funcs: {[string]: number}) => console.log(JSON.stringify(funcs, null, 2))),
    bus.scan().then((devices: Array<AddrType>) => console.log(JSON.stringify(devices, null, 2))),
  ]);

  // Initizalize devices
  const weatherSensor = new Device(bus, 0x77);
  const lightSensor = new Device(bus, 0x1d);

  await weatherSensor.writeByte(0x23, 0b1 | 0b100);
  await lightSensor.writeByte(0x25, 0x0f);

  return Promise.all([
    weatherSensor.readWord(0x50),
    weatherSensor.readWord(0x52),
    lightSensor.readWord(0x30),
  ])
    .then(([temperature, pressure, light]: Array<WordType>) => {
      console.log(`The temperature is ${temperature}`);
      console.log(`The pressure is ${pressure}`);
      console.log(`The light is ${light}`);
    });
};

main()
  .then(() => process.exit(0))
  .catch((error: Error) => {
    console.error(error.message);
    process.exit(1);
  });

File ./examples/usage.js

For more information, consult the API docs

Extending Device

However, you can also extend the Device to work with your i2c devices:

// @flow
/* eslint-disable no-console */
import { Bus, Device } from '../src';
import type { ByteType, WordType } from '../src/types';

class WeatherSensor extends Device {
  constructor(bus: Bus) {
    super(bus, 0x72);
  }

  writeConfig(config: ByteType) {
    return this.writeByte(0x24, config);
  }

  readTemperature() {
    return this.readWord(0x50);
  }

  readPressure() {
    return this.readWord(0x52);
  }
}

const main = async () => {
  const bus = new Bus();
  const weatherSensor = new WeatherSensor(bus);

  await bus.open();

  await weatherSensor.writeConfig(0b1 | 0b100);

  return Promise.all([
    weatherSensor.readTemperature(),
    weatherSensor.readPressure(),
  ])
    .then(([temperature, pressure]: Array<WordType>) => {
      console.log(`The temperature is ${temperature}°C`);
      console.log(`The pressure is ${pressure}Pa`);
    });
};

main()
  .then(() => process.exit(0))
  .catch((error: Error) => {
    console.error(error.message);
    process.exit(1);
  });

File ./examples/extendingDevice.js

For more information, consult the API docs

Tests

To run the tests just type:

yarn test

However it is recomended to run the e2e tests to ensure that everything works well.

BUS_NUMBER=1 yarn test:e2e

mock/createI2cBus

createI2cBus is a helper bus to be able to test your code using the library, and ensure that your code is doing what you want.

import { Bus } from '../src';

const BUS_NUMBER = 1;

jest.mock('i2c-bus', () => {
  const createI2cBus = require('../src/mock/createI2cBus').default; // eslint-disable-line global-require

  return createI2cBus({
    busNumber: 1,
    devices: {
      0x0f: Buffer.from(Array.from(Array(0xff).keys()).reverse()),
      0xf0: Buffer.from(Array.from(Array(0xff).keys())),
    },
    funcs: {
      read: 0x01,
      write: 0x02,
    },
  });
});

const setup = async (busNumber) => {
  const bus = new Bus(busNumber);

  await bus.open();

  return {
    bus,
    addToQueue: jest.spyOn(bus, 'addToQueue'),
    physicalBus: bus.bus.physicalBus,
  };
};

describe('Bus', () => {
  describe('i2cFuncs', () => {
    it('calls the i2cBus function through the promise queue', async () => {
      const { bus, addToQueue, physicalBus } = await setup(BUS_NUMBER);

      const result = await bus.i2cFuncs();

      expect(addToQueue).toHaveBeenCalledWith('i2cFuncsAsync');
      expect(result).toBe(physicalBus.funcs);
    });
  });
  describe('scan', () => {
    it('calls the i2cBus function through the promise queue', async () => {
      const { bus, addToQueue, physicalBus } = await setup(BUS_NUMBER);

      const result = await bus.scan();

      expect(addToQueue).toHaveBeenCalledWith('scanAsync');
      expect(result).toEqual(Object.keys(physicalBus.devices).map(addr => parseInt(addr, 10)));
    });
  });
});

File ./examples/tests.js

Be aware that you're working with a real device, the tests won't be much meaningful. And many things can fail IRL. It's always recommendable to write e2e tests to run in a real device.

Dependencies

bluebird: Full featured Promises/A+ implementation with exceptionally good performance
i2c-bus: I2C serial bus access with Node.js
p-queue: Promise queue with concurrency control