can-message/index.js

utility functions for handling CAN data from comma.ai panda

/*
  CAN UTILS
*/

export const CAN_TRANSMIT = 1;
export const CAN_EXTENDED = 4;

const CAN_MSG_LENGTH = 16;

export function unpackCAN (data): Array<CanMsg> {
  // Data must be a multiple of CAN_MSG_LENGTH
  if (data.byteLength % CAN_MSG_LENGTH !== 0) {
    let err = new Error('can-message.unpackCAN: byteLength must be a multiple of ' + CAN_MSG_LENGTH);
    throw err;
  }

  const msgs = [];

  for (let i = 0; i < data.byteLength; i += CAN_MSG_LENGTH) {
     let dat = data.slice(i, i + CAN_MSG_LENGTH);

     let datView = Buffer.from(dat);

     let f1 = datView.readInt32LE(0), f2 = datView.readInt32LE(4);
     let address;
     if ((f1 & CAN_EXTENDED) >>> 0) {
      address = f1 >>> 3;
     } else {
      address = f1 >>> 21;
     }

     let busTime = (f2 >>> 16);
     let canMsgData = new Buffer(dat.slice(8, 8 + (f2 & 0xF)));
     let bus = ((f2 >> 4) & 0xF) & 0xFF;

     let msg: CanMsg = { address, busTime, data: canMsgData, bus };
     msgs.push(msg);
   }

   return msgs;
}

export function packCAN (canMessage): Buffer {
  var { address, data, bus } = canMessage;

  if (data.byteLength > 8) {
    let err = new Error('can-message.packCAN: byteLength cannot be greater than 8');
    throw err;
  }

  if (address >= 0x800) {
    address = ((address << 3) | CAN_TRANSMIT | CAN_EXTENDED) >>> 0;
  } else {
    address = ((address << 21) | CAN_TRANSMIT) >>> 0;
  }

  let buf = Buffer.alloc(0x10);

  buf.writeUInt32LE(address);
  buf.writeUInt32LE((data.byteLength | (bus << 4)) >>> 0, 4);
  data.copy(buf, 8);

  return buf;
}