node-web-i2c/index.ts

import { openPromisified } from "i2c-bus";

const I2CPortMapSizeMax = 32;

const Uint16Max = 65535;

function parseUint16(string: string) {
  const n = Number.parseInt(string, 10);
  if (0 <= n && n <= Uint16Max) return n;
  else throw new RangeError(`Must be between 0 and ${Uint16Max}.`);
}

type PortNumber = number;
type PortName = string;

type I2CSlaveAddress = number;

export class I2CAccess {
  private readonly _ports: I2CPortMap;

  constructor(ports?: I2CPortMap) {
    this._ports = ports == null ? new I2CPortMap() : ports;
  }

  get ports() {
    return this._ports;
  }
}

/**
 * Different from Web GPIO API specification.
 */
export class I2CPortMap extends Map<PortNumber, I2CPort> {
  getByName(portName: PortName) {
    const matches = /^i2c-(\d+)$/.exec(portName);
    return matches == null ? undefined : this.get(parseUint16(matches[1]));
  }
}

export class I2CPort {
  private readonly _portNumber: PortNumber;

  constructor(portNumber: PortNumber) {
    this._portNumber = parseUint16(portNumber.toString());
  }

  get portNumber() {
    return this._portNumber;
  }

  get portName() {
    return `i2c-${this.portNumber}`;
  }

  async open(slaveAddress: I2CSlaveAddress): Promise<I2CSlaveDevice> {
    const bus = await openPromisified(this.portNumber).catch(error => {
      throw new OperationError(error);
    });

    return {
      slaveAddress,
      read8: cmd => bus.readByte(slaveAddress, cmd),
      read16: cmd => bus.readWord(slaveAddress, cmd),
      write8: (cmd, byte) => bus.writeByte(slaveAddress, cmd, byte),
      write16: (cmd, word) => bus.writeWord(slaveAddress, cmd, word)
    };
  }
}

export interface I2CSlaveDevice {
  readonly slaveAddress: I2CSlaveAddress;

  read8(registerNumber: number): Promise<number>;
  read16(registerNumber: number): Promise<number>;
  write8(registerNumber: number, value: number): Promise<number>;
  write16(registerNumber: number, value: number): Promise<number>;
}

export class OperationError extends Error {}

export async function requestI2CAccess(): Promise<I2CAccess> {
  const ports = new I2CPortMap(
    [...Array(I2CPortMapSizeMax).keys()].map(portNumber => [
      portNumber,
      new I2CPort(portNumber)
    ])
  );

  return new I2CAccess(ports);
}