dynamixel
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Node.js library for controlling DYNAMIXEL servo motors via U2D2 interface with Protocol 2.0 support
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JavaScript
import { HEADER, INSTRUCTIONS, ERROR_FLAGS, MIN_PACKET_LENGTH } from './constants.js';
/**
* DYNAMIXEL Protocol 2.0 implementation
* Handles packet construction, parsing, and CRC calculation
*/
export class Protocol2 {
/**
* Calculate CRC-16 for DYNAMIXEL Protocol 2.0
* Based on official ROBOTIS code: http://support.robotis.com/en/product/actuator/dynamixel_pro/communication/crc.htm
* CRC-16 (IBM/ANSI) - Polynomial: x16 + x15 + x2 + 1 (0x8005), Initial Value: 0
* @param {Buffer|Array} data - Data to calculate CRC for
* @returns {number} - 16-bit CRC value
*/
static calculateCRC(data) {
const crcTable = [
0x0000, 0x8005, 0x800F, 0x000A, 0x801B, 0x001E, 0x0014, 0x8011,
0x8033, 0x0036, 0x003C, 0x8039, 0x0028, 0x802D, 0x8027, 0x0022,
0x8063, 0x0066, 0x006C, 0x8069, 0x0078, 0x807D, 0x8077, 0x0072,
0x0050, 0x8055, 0x805F, 0x005A, 0x804B, 0x004E, 0x0044, 0x8041,
0x80C3, 0x00C6, 0x00CC, 0x80C9, 0x00D8, 0x80DD, 0x80D7, 0x00D2,
0x00F0, 0x80F5, 0x80FF, 0x00FA, 0x80EB, 0x00EE, 0x00E4, 0x80E1,
0x00A0, 0x80A5, 0x80AF, 0x00AA, 0x80BB, 0x00BE, 0x00B4, 0x80B1,
0x8093, 0x0096, 0x009C, 0x8099, 0x0088, 0x808D, 0x8087, 0x0082,
0x8183, 0x0186, 0x018C, 0x8189, 0x0198, 0x819D, 0x8197, 0x0192,
0x01B0, 0x81B5, 0x81BF, 0x01BA, 0x81AB, 0x01AE, 0x01A4, 0x81A1,
0x01E0, 0x81E5, 0x81EF, 0x01EA, 0x81FB, 0x01FE, 0x01F4, 0x81F1,
0x81D3, 0x01D6, 0x01DC, 0x81D9, 0x01C8, 0x81CD, 0x81C7, 0x01C2,
0x0140, 0x8145, 0x814F, 0x014A, 0x815B, 0x015E, 0x0154, 0x8151,
0x8173, 0x0176, 0x017C, 0x8179, 0x0168, 0x816D, 0x8167, 0x0162,
0x8123, 0x0126, 0x012C, 0x8129, 0x0138, 0x813D, 0x8137, 0x0132,
0x0110, 0x8115, 0x811F, 0x011A, 0x810B, 0x010E, 0x0104, 0x8101,
0x8303, 0x0306, 0x030C, 0x8309, 0x0318, 0x831D, 0x8317, 0x0312,
0x0330, 0x8335, 0x833F, 0x033A, 0x832B, 0x032E, 0x0324, 0x8321,
0x0360, 0x8365, 0x836F, 0x036A, 0x837B, 0x037E, 0x0374, 0x8371,
0x8353, 0x0356, 0x035C, 0x8359, 0x0348, 0x834D, 0x8347, 0x0342,
0x03C0, 0x83C5, 0x83CF, 0x03CA, 0x83DB, 0x03DE, 0x03D4, 0x83D1,
0x83F3, 0x03F6, 0x03FC, 0x83F9, 0x03E8, 0x83ED, 0x83E7, 0x03E2,
0x83A3, 0x03A6, 0x03AC, 0x83A9, 0x03B8, 0x83BD, 0x83B7, 0x03B2,
0x0390, 0x8395, 0x839F, 0x039A, 0x838B, 0x038E, 0x0384, 0x8381,
0x0280, 0x8285, 0x828F, 0x028A, 0x829B, 0x029E, 0x0294, 0x8291,
0x82B3, 0x02B6, 0x02BC, 0x82B9, 0x02A8, 0x82AD, 0x82A7, 0x02A2,
0x82E3, 0x02E6, 0x02EC, 0x82E9, 0x02F8, 0x82FD, 0x82F7, 0x02F2,
0x02D0, 0x82D5, 0x82DF, 0x02DA, 0x82CB, 0x02CE, 0x02C4, 0x82C1,
0x8243, 0x0246, 0x024C, 0x8249, 0x0258, 0x825D, 0x8257, 0x0252,
0x0270, 0x8275, 0x827F, 0x027A, 0x826B, 0x026E, 0x0264, 0x8261,
0x0220, 0x8225, 0x822F, 0x022A, 0x823B, 0x023E, 0x0234, 0x8231,
0x8213, 0x0216, 0x021C, 0x8219, 0x0208, 0x820D, 0x8207, 0x0202
];
let crcAccum = 0;
const dataArray = Array.isArray(data) ? data : Array.from(data);
// Official ROBOTIS algorithm:
// for(j = 0; j < data_blk_size; j++) {
// i = ((unsigned short)(crc_accum >> 8) ^ data_blk_ptr[j]) & 0xFF;
// crc_accum = (crc_accum << 8) ^ crc_table[i];
// }
for (let j = 0; j < dataArray.length; j++) {
const i = ((crcAccum >> 8) ^ dataArray[j]) & 0xFF;
crcAccum = (crcAccum << 8) ^ crcTable[i];
}
// Ensure 16-bit result
crcAccum = crcAccum & 0xFFFF;
return crcAccum;
}
/**
* Create an instruction packet
* @param {number} id - DYNAMIXEL ID (0-252, 0xFE for broadcast)
* @param {number} instruction - Instruction byte
* @param {Array|Buffer} parameters - Parameter data
* @returns {Buffer} - Complete instruction packet
*/
static createInstructionPacket(id, instruction, parameters = []) {
const paramArray = Array.isArray(parameters) ? parameters : Array.from(parameters);
const length = 3 + paramArray.length; // Instruction + Parameters + CRC(2)
// Build packet without CRC
const packet = [
...HEADER, // Header: 0xFF 0xFF 0xFD 0x00
id, // Packet ID
length & 0xFF, // Length low byte
(length >> 8) & 0xFF, // Length high byte
instruction, // Instruction
...paramArray // Parameters
];
// Calculate CRC for the entire packet (excluding only the CRC bytes)
// According to ROBOTIS documentation: CRC is calculated on the full packet
const crc = this.calculateCRC(packet);
// Add CRC to packet
packet.push(crc & 0xFF); // CRC low byte
packet.push((crc >> 8) & 0xFF); // CRC high byte
return Buffer.from(packet);
}
/**
* Parse a status packet
* @param {Buffer} buffer - Raw packet data
* @returns {Object|null} - Parsed packet or null if invalid
*/
static parseStatusPacket(buffer) {
if (!buffer || buffer.length < MIN_PACKET_LENGTH) {
return null;
}
// Check header
if (buffer[0] !== HEADER[0] || buffer[1] !== HEADER[1] ||
buffer[2] !== HEADER[2] || buffer[3] !== HEADER[3]) {
return null;
}
const id = buffer[4];
const length = buffer[5] | (buffer[6] << 8);
const instruction = buffer[7];
const error = buffer[8];
// Check if we have enough data for the complete packet
if (buffer.length < 9 + length - 2) {
return null;
}
// Extract parameters (everything between error and CRC)
const paramLength = length - 4; // length - instruction - error - CRC(2)
const parameters = Array.from(buffer.slice(9, 9 + paramLength));
// Extract CRC
const crcReceived = buffer[9 + paramLength] | (buffer[9 + paramLength + 1] << 8);
// Verify CRC - calculate on entire packet excluding only the CRC bytes
const crcData = Array.from(buffer.slice(0, 9 + paramLength));
const crcCalculated = this.calculateCRC(crcData);
if (crcReceived !== crcCalculated) {
throw new Error(`CRC mismatch: received ${crcReceived.toString(16)}, calculated ${crcCalculated.toString(16)}`);
}
return {
id,
instruction,
error,
parameters,
length,
raw: buffer
};
}
/**
* Create a PING instruction packet
* @param {number} id - DYNAMIXEL ID (0-252, 0xFE for broadcast)
* @returns {Buffer} - PING instruction packet
*/
static createPingPacket(id) {
return this.createInstructionPacket(id, INSTRUCTIONS.PING, []);
}
/**
* Parse PING status packet to extract device information
* @param {Object} statusPacket - Parsed status packet
* @returns {Object|null} - Device information or null if not a PING response
*/
static parsePingResponse(statusPacket) {
if (!statusPacket || statusPacket.instruction !== INSTRUCTIONS.STATUS) {
return null;
}
if (statusPacket.parameters.length < 3) {
return null;
}
const modelNumber = statusPacket.parameters[0] | (statusPacket.parameters[1] << 8);
const firmwareVersion = statusPacket.parameters[2];
return {
id: statusPacket.id,
modelNumber,
firmwareVersion,
error: statusPacket.error
};
}
/**
* Check if buffer contains a complete packet
* @param {Buffer} buffer - Buffer to check
* @returns {number} - Length of complete packet, or 0 if incomplete
*/
static getCompletePacketLength(buffer) {
if (!buffer || buffer.length < 7) {
return 0;
}
// Check for header
if (buffer[0] !== HEADER[0] || buffer[1] !== HEADER[1] ||
buffer[2] !== HEADER[2] || buffer[3] !== HEADER[3]) {
return 0;
}
const length = buffer[5] | (buffer[6] << 8);
const totalLength = 7 + length; // Header(4) + ID(1) + Length(2) + Data(length)
return buffer.length >= totalLength ? totalLength : 0;
}
/**
* Convert error code to human-readable string
* @param {number} errorCode - Error code from status packet
* @returns {string} - Error description
*/
static getErrorDescription(errorCode) {
const errors = [];
if (errorCode & ERROR_FLAGS.RESULT_FAIL) errors.push('Result Fail');
if (errorCode & ERROR_FLAGS.INSTRUCTION_ERROR) errors.push('Instruction Error');
if (errorCode & ERROR_FLAGS.CRC_ERROR) errors.push('CRC Error');
if (errorCode & ERROR_FLAGS.DATA_RANGE_ERROR) errors.push('Data Range Error');
if (errorCode & ERROR_FLAGS.DATA_LENGTH_ERROR) errors.push('Data Length Error');
if (errorCode & ERROR_FLAGS.DATA_LIMIT_ERROR) errors.push('Data Limit Error');
if (errorCode & ERROR_FLAGS.ACCESS_ERROR) errors.push('Access Error');
return errors.length > 0 ? errors.join(', ') : 'No Error';
}
}