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Sample Code

Java Protocol 2.0

Java Sync Read Write Protocol 2.0

/*
 * SyncReadWrite.java
 *
 *  Created on: 2016. 6. 23.
 *      Author: Ryu Woon Jung (Leon)
 */

//
// *********     Sync Read and Sync Write Example      *********
//
//
// Available Dynamixel model on this example : All models using Protocol 2.0
// This example is designed for using two Dynamixel PRO 54-200, and an USB2DYNAMIXEL.
// To use another Dynamixel model, such as X series, see their details in E-Manual(support.robotis.com) and edit below variables yourself.
// Be sure that Dynamixel PRO properties are already set as %% ID : 1 / Baudnum : 3 (Baudrate : 1000000 [1M])
//

import java.util.Scanner;

public class SyncReadWrite
{
  public static void main(String[] args)
  {
    // Control table address
    short ADDR_PRO_TORQUE_ENABLE        = 562;                 // Control table address is different in Dynamixel model
    short ADDR_PRO_GOAL_POSITION        = 596;
    short ADDR_PRO_PRESENT_POSITION     = 611;

    // Data Byte Length
    short LEN_PRO_GOAL_POSITION         = 4;
    short LEN_PRO_PRESENT_POSITION      = 4;

    // Protocol version
    int PROTOCOL_VERSION                = 2;                   // See which protocol version is used in the Dynamixel

    // Default setting
    byte DXL1_ID                        = 1;                   // Dynamixel ID: 1
    byte DXL2_ID                        = 2;                   // Dynamixel ID: 2
    int BAUDRATE                        = 1000000;
    String DEVICENAME                   = "/dev/ttyUSB0";      // Check which port is being used on your controller
                                                               // ex) "COM1"   Linux: "/dev/ttyUSB0"

    byte TORQUE_ENABLE                  = 1;                   // Value for enabling the torque
    byte TORQUE_DISABLE                 = 0;                   // Value for disabling the torque
    int DXL_MINIMUM_POSITION_VALUE      = -150000;             // Dynamixel will rotate between this value
    int DXL_MAXIMUM_POSITION_VALUE      = 150000;              // and this value (note that the Dynamixel would not move when the position value is out of movable range. Check e-manual about the range of the Dynamixel you use.)
    int DXL_MOVING_STATUS_THRESHOLD     = 20;                  // Dynamixel moving status threshold

    String KEY_FOR_ESCAPE               = "e";                 // Key for escape

    int COMM_SUCCESS                    = 0;                   // Communication Success result value
    int COMM_TX_FAIL                    = -1001;               // Communication Tx Failed

    // Instead of getch
    Scanner scanner = new Scanner(System.in);

    // Initialize Dynamixel class for java
    Dynamixel dynamixel = new Dynamixel();

    // Initialize PortHandler Structs
    // Set the port path
    // Get methods and members of PortHandlerLinux or PortHandlerWindows
    int port_num = dynamixel.portHandler(DEVICENAME);

    // Initialize PacketHandler Structs
    dynamixel.packetHandler();

    // Initialize Groupsyncwrite instance
    int groupwrite_num = dynamixel.groupSyncWrite(port_num, PROTOCOL_VERSION, ADDR_PRO_GOAL_POSITION, LEN_PRO_GOAL_POSITION);

    // Initialize Groupsyncread Structs for Present Position
    int groupread_num = dynamixel.groupSyncRead(port_num, PROTOCOL_VERSION, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);

    int index = 0;
    int dxl_comm_result = COMM_TX_FAIL;                         // Communication result
    Boolean dxl_addparam_result = false;                        // AddParam result
    Boolean dxl_getdata_result = false;                         // GetParam result
    int[] dxl_goal_position = new int[]{DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE};         // Goal position

    byte dxl_error = 0;                                         // Dynamixel error
    int dxl1_present_position = 0, dxl2_present_position = 0;   // Present position

    // Open port
    if (dynamixel.openPort(port_num))
    {
      System.out.println("Succeeded to open the port!");
    }
    else
    {
      System.out.println("Failed to open the port!");
      System.out.println("Press any key to terminate...");
      scanner.nextLine();
      return;
    }

    // Set port baudrate
    if (dynamixel.setBaudRate(port_num, BAUDRATE))
    {
      System.out.println("Succeeded to change the baudrate!");
    }
    else
    {
      System.out.println("Failed to change the baudrate!");
      System.out.println("Press any key to terminate...");
      scanner.nextLine();
      return;
    }

    // Enable Dynamixel#1 Torque
    dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL1_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_ENABLE);
    if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
    {
      dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);
    }
    else if ((dxl_error = dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION)) != 0)
    {
      dynamixel.printRxPacketError(PROTOCOL_VERSION, dxl_error);
    }
    else
    {
      System.out.printf("Dynamixel#%d has been successfully connected\n", DXL1_ID);
    }

    // Enable Dynamixel#2 Torque
    dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL2_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_ENABLE);
    if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
    {
      dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);
    }
    else if ((dxl_error = dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION)) != 0)
    {
      dynamixel.printRxPacketError(PROTOCOL_VERSION, dxl_error);
    }
    else
    {
      System.out.printf("Dynamixel#%d has been successfully connected\n", DXL2_ID);
    }

    // Add parameter storage for Dynamixel#1 present position value
    dxl_addparam_result = dynamixel.groupSyncReadAddParam(groupread_num, DXL1_ID);
    if (dxl_addparam_result != true)
    {
      System.out.printf("[ID: %d] groupSyncRead addparam failed\n", DXL1_ID);
      return;
    }

    // Add parameter storage for Dynamixel#2 present position value
    dxl_addparam_result = dynamixel.groupSyncReadAddParam(groupread_num, DXL2_ID);
    if (dxl_addparam_result != true)
    {
      System.out.printf("[ID: %d] groupSyncRead addparam failed\n", DXL2_ID);
      return;
    }

    while (true)
    {
      System.out.println("Press enter to continue! (or press e then enter to quit!)");
      if(scanner.nextLine().equals(KEY_FOR_ESCAPE))
        break;

      // Add Dynamixel#1 goal position value to the Syncwrite storage
      dxl_addparam_result = dynamixel.groupSyncWriteAddParam(groupwrite_num, DXL1_ID, dxl_goal_position[index], LEN_PRO_GOAL_POSITION);
      if (dxl_addparam_result != true)
      {
        System.out.printf("[ID: %d] groupSyncWrite addparam failed\n", DXL1_ID);
        return;
      }

      // Add Dynamixel#2 goal position value to the Syncwrite parameter storage
      dxl_addparam_result = dynamixel.groupSyncWriteAddParam(groupwrite_num, DXL2_ID, dxl_goal_position[index], LEN_PRO_GOAL_POSITION);
      if (dxl_addparam_result != true)
      {
        System.out.printf("[ID: %d] groupSyncWrite addparam failed\n", DXL2_ID);
        return;
      }

      // Syncwrite goal position
      dynamixel.groupSyncWriteTxPacket(groupwrite_num);
      if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
        dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);

      // Clear syncwrite parameter storage
      dynamixel.groupSyncWriteClearParam(groupwrite_num);

      do
      {
        // Syncread present position
        dynamixel.groupSyncReadTxRxPacket(groupread_num);
        if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
          dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);

        // Check if groupsyncread data of Dynamixel#1 is available
        dxl_getdata_result = dynamixel.groupSyncReadIsAvailable(groupread_num, DXL1_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);
        if (dxl_getdata_result != true)
        {
          System.out.printf("[ID: %d] groupSyncRead getdata failed\n", DXL1_ID);
          return;
        }

        // Check if groupsyncread data of Dynamixel#2 is available
        dxl_getdata_result = dynamixel.groupSyncReadIsAvailable(groupread_num, DXL2_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);
        if (dxl_getdata_result != true)
        {
          System.out.printf("[ID: %d] groupSyncRead getdata failed\n", DXL2_ID);
          return;
        }

        // Get Dynamixel#1 present position value
        dxl1_present_position = dynamixel.groupSyncReadGetData(groupread_num, DXL1_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);

        // Get Dynamixel#2 present position value
        dxl2_present_position = dynamixel.groupSyncReadGetData(groupread_num, DXL2_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);

        System.out.printf("[ID: %d] GoalPos: %d  PresPos: %d [ID: %d] GoalPos: %d  PresPos: %d\n", DXL1_ID, dxl_goal_position[index], dxl1_present_position, DXL2_ID, dxl_goal_position[index], dxl2_present_position);

      } while ((Math.abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD) || (Math.abs(dxl_goal_position[index] - dxl2_present_position) > DXL_MOVING_STATUS_THRESHOLD));

      // Change goal position
      if (index == 0)
      {
        index = 1;
      }
      else
      {
        index = 0;
      }
    }

    // Disable Dynamixel#1 Torque
    dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL1_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_DISABLE);
    if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
    {
      dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);
    }
    else if ((dxl_error = dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION)) != 0)
    {
      dynamixel.printRxPacketError(PROTOCOL_VERSION, dxl_error);
    }

    // Disable Dynamixel#2 Torque
    dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL2_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_DISABLE);
    if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
    {
      dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);
    }
    else if ((dxl_error = dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION)) != 0)
    {
      dynamixel.printRxPacketError(PROTOCOL_VERSION, dxl_error);
    }

    // Close port
    dynamixel.closePort(port_num);

    return;
  }
}

import java.util.Scanner;

The functions Scanner.* for I, are in the example code, and it uses java.util.Scanner library.

// Control table address
short ADDR_PRO_TORQUE_ENABLE        = 562;                 // Control table address is different in Dynamixel model
short ADDR_PRO_GOAL_POSITION        = 596;
short ADDR_PRO_PRESENT_POSITION     = 611;

// Data Byte Length
short LEN_PRO_GOAL_POSITION         = 4;
short LEN_PRO_PRESENT_POSITION      = 4;

Dynamixel series have their own control tables: Addresses and Byte Length in each items. To control one of the items, its address (and length if necessary) is required. Find your requirements in http://support.robotis.com/.

// Protocol version
int PROTOCOL_VERSION                = 2;                   // See which protocol version is used in the Dynamixel

Dynamixel uses either or both protocols: Protocol 1.0 and Protocol 2.0. Choose one of the Protocol which is appropriate in the Dynamixel.

// Default setting
byte DXL1_ID                        = 1;                   // Dynamixel ID: 1
byte DXL2_ID                        = 2;                   // Dynamixel ID: 2
int BAUDRATE                        = 1000000;
String DEVICENAME                   = "/dev/ttyUSB0";      // Check which port is being used on your controller
                                                           // ex) "COM1"   Linux: "/dev/ttyUSB0"

byte TORQUE_ENABLE                  = 1;                   // Value for enabling the torque
byte TORQUE_DISABLE                 = 0;                   // Value for disabling the torque
int DXL_MINIMUM_POSITION_VALUE      = -150000;             // Dynamixel will rotate between this value
int DXL_MAXIMUM_POSITION_VALUE      = 150000;              // and this value (note that the Dynamixel would not move when the position value is out of movable range. Check e-manual about the range of the Dynamixel you use.)
int DXL_MOVING_STATUS_THRESHOLD     = 20;                  // Dynamixel moving status threshold

String KEY_FOR_ESCAPE               = "e";                 // Key for escape

Here we set some variables to let you freely change them and use them to run the example code.

As the document previously said in previous chapter, customize Dynamixel control table items, such as DXL_ID number, communication BAUDRATE, and the DEVICENAME, on your own terms of needs. In particular, BAUDRATE and DEVICENAME have systematical dependencies on your controller, so make clear what kind of communication method you will use.

The example uses two Dynamixels DXL1_ID, DXL2_ID connected with the port DEVICENAME.

Dynamixel basically needs the TORQUE_ENABLE to be rotating or give you its internal information. On the other hand, it doesn’t need torque enabled if you get your goal, so finally do TORQUE_DISABLE to prepare to the next sequence.

Since the Dynamixel has its own rotation range, it may shows malfunction if your request on your dynamixel is out of range. For example, Dynamixel MX-28 and Dynamixel PRO 54-200 has its rotatable range as 0 ~ 4028 and -250950 ~ 250950, each.

DXL_MOVING_STATUS_THRESHOLD acts as a criteria for verifying its rotation stopped.

int COMM_SUCCESS                    = 0;                   // Communication Success result value
int COMM_TX_FAIL                    = -1001;               // Communication Tx Failed

Each of the variables above show the meaning of the communication result value.

// Instead of getch
Scanner scanner = new Scanner(System.in);

This initializes instance for key detection.

// Initialize Dynamixel class for java
Dynamixel dynamixel = new Dynamixel();

This initializes Dynamixel class.

// Initialize PortHandler Structs
// Set the port path
// Get methods and members of PortHandlerLinux or PortHandlerWindows
int port_num = dynamixel.portHandler(DEVICENAME);

portHandler() function sets port path as DEVICENAME and get port_num, and prepares an appropriate functions for port control in controller OS automatically. port_num would be used in many functions in the body of the code to specify the port for use.

// Initialize PacketHandler Structs
dynamixel.packetHandler();

packetHandler() function initializes parameters used for packet construction and packet storing.

// Initialize Groupsyncwrite instance
int groupwrite_num = dynamixel.groupSyncWrite(port_num, PROTOCOL_VERSION, ADDR_PRO_GOAL_POSITION, LEN_PRO_GOAL_POSITION);

groupSyncWrite() function initializes grouped parameters used for packet construction and packet storing. The utility functions of sync write deals simultaneously with more than one Dynamixel through #port_num port, building packets by the function which uses PROTOCOL_VERSION, and writing LEN_PRO_GOAL_POSITION bytes of the values on the address ADDR_PRO_GOAL_POSITION.

// Initialize Groupsyncread Structs for Present Position
int groupread_num = dynamixel.groupSyncRead(port_num, PROTOCOL_VERSION, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);

groupSyncRead() function initializes grouped parameters used for packet construction and packet storing. The utility functions of sync read deals simultaneously with more than one Dynamixel through #port_num port, building packets by the function which uses PROTOCOL_VERSION, and requesting LEN_PRO_PRESENT_POSITION bytes of the values on the address ADDR_PRO_GOAL_POSITION.

int index = 0;
int dxl_comm_result = COMM_TX_FAIL;                         // Communication result
Boolean dxl_addparam_result = false;                        // AddParam result
Boolean dxl_getdata_result = false;                         // GetParam result
int[] dxl_goal_position = new int[]{DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE};         // Goal position

byte dxl_error = 0;                                         // Dynamixel error
int dxl1_present_position = 0, dxl2_present_position = 0;   // Present position

index variable points the direction to where the Dynamixel should be rotated.

dxl_comm_result indicates which error has been occurred during packet communication.

dxl_addparam_result indicates the result of parameter addition used for sync/bulk related functions

dxl_getdata_result indicates the result of data reception used for sync/bulk related functions

dxl_goal_position stores goal points of Dynamixel rotation.

dxl_error shows the internal error in Dynamixel.

dxl1_present_position and dxl2_present_position view where now each Dynamixel points out.

// Open port
if (dynamixel.openPort(port_num))
{
  System.out.println("Succeeded to open the port!");
}
else
{
  System.out.println("Failed to open the port!");
  System.out.println("Press any key to terminate...");
  scanner.nextLine();
  return;
}

First, controller opens #port_num port to do serial communication with the Dynamixel. If it fails to open the port, the example will be terminated.

// Set port baudrate
if (dynamixel.setBaudRate(port_num, BAUDRATE))
{
  System.out.println("Succeeded to change the baudrate!");
}
else
{
  System.out.println("Failed to change the baudrate!");
  System.out.println("Press any key to terminate...");
  scanner.nextLine();
  return;
}

Secondly, the controller sets the communication BAUDRATE at #port_num port opened previously.

// Enable Dynamixel#1 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL1_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_ENABLE);
if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
{
  dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);
}
else if ((dxl_error = dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION)) != 0)
{
  dynamixel.printRxPacketError(PROTOCOL_VERSION, dxl_error);
}
else
{
  System.out.printf("Dynamixel#%d has been successfully connected\n", DXL1_ID);
}

// Enable Dynamixel#2 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL2_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_ENABLE);
if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
{
  dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);
}
else if ((dxl_error = dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION)) != 0)
{
  dynamixel.printRxPacketError(PROTOCOL_VERSION, dxl_error);
}
else
{
  System.out.printf("Dynamixel#%d has been successfully connected\n", DXL2_ID);
}

As mentioned in the document, above code enables each Dynamixel`s torque to set their status as being ready to move.

write1ByteTxRx() function orders to the #DXL1_ID and #DXL2_ID Dynamixels in PROTOCOL_VERSION communication protocol through #port_num port, writing 1 byte of TORQUE_ENABLE value to ADDR_PRO_TORQUE_ENABLE address. The function checks Tx/Rx result and receives Hardware error. getLastTxRxResult() function and getLastRxPacketError() function get either, and then printTxRxResult() function and printRxPacketError() function show results on the console window if any communication error or Hardware error has been occurred.

// Add parameter storage for Dynamixel#1 present position value
dxl_addparam_result = dynamixel.groupSyncReadAddParam(groupread_num, DXL1_ID);
if (dxl_addparam_result != true)
{
  System.out.printf("[ID: %d] groupSyncRead addparam failed\n", DXL1_ID);
  return;
}

// Add parameter storage for Dynamixel#2 present position value
dxl_addparam_result = dynamixel.groupSyncReadAddParam(groupread_num, DXL2_ID);
if (dxl_addparam_result != true)
{
  System.out.printf("[ID: %d] groupSyncRead addparam failed\n", DXL2_ID);
  return;
}

groupSyncReadAddParam() function stores the Dynamixel ID of required data to the syncread target Dynamixel list.

while (true)
{
  System.out.println("Press enter to continue! (or press e then enter to quit!)");
  if(scanner.nextLine().equals(KEY_FOR_ESCAPE))
    break;

  // Add Dynamixel#1 goal position value to the Syncwrite storage
  dxl_addparam_result = dynamixel.groupSyncWriteAddParam(groupwrite_num, DXL1_ID, dxl_goal_position[index], LEN_PRO_GOAL_POSITION);
  if (dxl_addparam_result != true)
  {
    System.out.printf("[ID: %d] groupSyncWrite addparam failed\n", DXL1_ID);
    return;
  }

  // Add Dynamixel#2 goal position value to the Syncwrite parameter storage
  dxl_addparam_result = dynamixel.groupSyncWriteAddParam(groupwrite_num, DXL2_ID, dxl_goal_position[index], LEN_PRO_GOAL_POSITION);
  if (dxl_addparam_result != true)
  {
    System.out.printf("[ID: %d] groupSyncWrite addparam failed\n", DXL2_ID);
    return;
  }

  // Syncwrite goal position
  dynamixel.groupSyncWriteTxPacket(groupwrite_num);
  if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);

  // Clear syncwrite parameter storage
  dynamixel.groupSyncWriteClearParam(groupwrite_num);

  do
  {
    // Syncread present position
    dynamixel.groupSyncReadTxRxPacket(groupread_num);
    if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
      dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);

    // Check if groupsyncread data of Dynamixel#1 is available
    dxl_getdata_result = dynamixel.groupSyncReadIsAvailable(groupread_num, DXL1_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);
    if (dxl_getdata_result != true)
    {
      System.out.printf("[ID: %d] groupSyncRead getdata failed\n", DXL1_ID);
      return;
    }

    // Check if groupsyncread data of Dynamixel#2 is available
    dxl_getdata_result = dynamixel.groupSyncReadIsAvailable(groupread_num, DXL2_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);
    if (dxl_getdata_result != true)
    {
      System.out.printf("[ID: %d] groupSyncRead getdata failed\n", DXL2_ID);
      return;
    }

    // Get Dynamixel#1 present position value
    dxl1_present_position = dynamixel.groupSyncReadGetData(groupread_num, DXL1_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);

    // Get Dynamixel#2 present position value
    dxl2_present_position = dynamixel.groupSyncReadGetData(groupread_num, DXL2_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION);

    System.out.printf("[ID: %d] GoalPos: %d  PresPos: %d [ID: %d] GoalPos: %d  PresPos: %d\n", DXL1_ID, dxl_goal_position[index], dxl1_present_position, DXL2_ID, dxl_goal_position[index], dxl2_present_position);

  } while ((Math.abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD) || (Math.abs(dxl_goal_position[index] - dxl2_present_position) > DXL_MOVING_STATUS_THRESHOLD));

  // Change goal position
  if (index == 0)
  {
    index = 1;
  }
  else
  {
    index = 0;
  }
}

During while() loop, the controller writes and reads each Dynamixel position through packet transmission/reception(Tx/Rx).

To continue their rotation, press any key except ESC.

groupSyncWriteAddParam() function stores the Dynamixel ID and its LEN_PRO_GOAL_POSITION bytes goal position dxl_goal_position to the syncwrite target Dynamixel list.

groupSyncWriteTxPacket() function orders to the Dynamixel #DXL1_ID and #DXL2_ID at the same time through #port_num, making it possible to write same pre-listed length bytes to same pre-listed address. The function checks Tx/Rx result. getLastTxRxResult() function gets it, and then printTxRxResult() function shows result on the console window if any communication error has been occurred.

groupSyncWriteClearParam() function clears the Dynamixel list of groupsyncwrite.

groupSyncReadTxRxPacket() function orders to the Dynamixel #DXL1_ID and #DXL2_ID at the same time through #port_num port, making it possible to read same pre-listed length(LEN_PRO_PRESENT_POSITION) of bytes from same pre-listed address(ADDR_PRO_PRESENT_POSITION). The function checks Tx/Rx result. getLastTxRxResult() function gets it, and then printTxRxResult() function shows result on the console window if any communication error has been occurred.

groupSyncReadIsAvailable() function checks if available data is in the groupsyncread data storage. The function returns false if no data is available in the storage.

groupSyncReadGetData() function pop the data received by groupSyncReadTxRxPacket() function out. In the example, it stores LEN_PRO_PRESENT_POSITION byte data got from ADDR_PRO_PRESENT_POSITION address of DXL1_ID andDXL2_ID Dynamixels.

groupSyncReadClearParam() function clears the Dynamixel list of groupsyncread.

Reading their present position will be ended when absolute value of (dxl_goal_position[index] - dxl1_present_position) or (dxl_goal_position[index] - dxl2_present_position) becomes smaller then DXL_MOVING_STATUS_THRESHOLD.

At last, it changes their direction to the counter-wise and waits for extra key input.

// Disable Dynamixel#1 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL1_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_DISABLE);
if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
{
  dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);
}
else if ((dxl_error = dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION)) != 0)
{
  dynamixel.printRxPacketError(PROTOCOL_VERSION, dxl_error);
}

// Disable Dynamixel#2 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL2_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_DISABLE);
if ((dxl_comm_result = dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION)) != COMM_SUCCESS)
{
  dynamixel.printTxRxResult(PROTOCOL_VERSION, dxl_comm_result);
}
else if ((dxl_error = dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION)) != 0)
{
  dynamixel.printRxPacketError(PROTOCOL_VERSION, dxl_error);
}

The controller frees the Dynamixels to be idle.

write1ByteTxRx() function orders to the #DXL1_ID and #DXL2_ID Dynamixels in PROTOCOL_VERSION communication protocol through #port_num port, writing 1 byte of TORQUE_DISABLE value to ADDR_PRO_TORQUE_ENABLE address. The function checks Tx/Rx result and receives Hardware error. getLastTxRxResult() function and getLastRxPacketError() function get either, and then printTxRxResult() function and printRxPacketError() function show results on the console window if any communication error or Hardware error has been occurred.

// Close port
dynamixel.closePort(port_num);

return;

Finally, port becomes disposed.