DYNAMIXEL SDK

CPP Sync Write Protocol 1.0

Description

This example writes goal positions to two DYNAMIXEL’s simultaneously and repeats to read each present positions until DYNAMIXEL stop moving. The funtions that are related with the Syncwrite handle the number of items that are near to each other in the Dynamixel control table on multiple DYNAMIXEL’s, such as the goal position and the goal velocity.
Available Dynamixel

All series using protocol 1.0

Sample code Parts

/*
 * sync_write.cpp
 *
 *  Created on: 2016. 2. 21.
 *      Author: leon
 */

//
// *********     Sync Write Example      *********
//
//
// Available Dynamixel model on this example : All models using Protocol 1.0
// This example is designed for using two Dynamixel MX-28, and an USB2DYNAMIXEL.
// To use another Dynamixel model, such as X series, see their details in E-Manual(support.robotis.com) and edit below "#define"d variables yourself.
// Be sure that Dynamixel MX properties are already set as %% ID : 1 / Baudnum : 1 (Baudrate : 1000000 [1M])
//

#ifdef __linux__
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#elif defined(_WIN32) || defined(_WIN64)
#include <conio.h>
#endif

#include <stdlib.h>
#include <stdio.h>

#include "dynamixel_sdk.h"                                  // Uses DYNAMIXEL SDK library

// Control table address
#define ADDR_MX_TORQUE_ENABLE           24                  // Control table address is different in Dynamixel model
#define ADDR_MX_GOAL_POSITION           30
#define ADDR_MX_PRESENT_POSITION        36

// Data Byte Length
#define LEN_MX_GOAL_POSITION            2
#define LEN_MX_PRESENT_POSITION         2

// Protocol version
#define PROTOCOL_VERSION                1.0                 // See which protocol version is used in the Dynamixel

// Default setting
#define DXL1_ID                         1                   // Dynamixel#1 ID: 1
#define DXL2_ID                         2                   // Dynamixel#2 ID: 2
#define BAUDRATE                        1000000
#define DEVICENAME                      "/dev/ttyUSB0"      // Check which port is being used on your controller
                                                            // ex) Windows: "COM1"   Linux: "/dev/ttyUSB0"

#define TORQUE_ENABLE                   1                   // Value for enabling the torque
#define TORQUE_DISABLE                  0                   // Value for disabling the torque
#define DXL_MINIMUM_POSITION_VALUE      100                 // Dynamixel will rotate between this value
#define DXL_MAXIMUM_POSITION_VALUE      4000                // 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.)
#define DXL_MOVING_STATUS_THRESHOLD     10                  // Dynamixel moving status threshold

#define ESC_ASCII_VALUE                 0x1b

int getch()
{
#ifdef __linux__
  struct termios oldt, newt;
  int ch;
  tcgetattr(STDIN_FILENO, &oldt);
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  ch = getchar();
  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
  return ch;
#elif defined(_WIN32) || defined(_WIN64)
  return _getch();
#endif
}

int kbhit(void)
{
#ifdef __linux__
  struct termios oldt, newt;
  int ch;
  int oldf;

  tcgetattr(STDIN_FILENO, &oldt);
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  oldf = fcntl(STDIN_FILENO, F_GETFL, 0);
  fcntl(STDIN_FILENO, F_SETFL, oldf | O_NONBLOCK);

  ch = getchar();

  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
  fcntl(STDIN_FILENO, F_SETFL, oldf);

  if (ch != EOF)
  {
    ungetc(ch, stdin);
    return 1;
  }

  return 0;
#elif defined(_WIN32) || defined(_WIN64)
  return _kbhit();
#endif
}

int main()
{
  // Initialize PortHandler instance
  // Set the port path
  // Get methods and members of PortHandlerLinux or PortHandlerWindows
  dynamixel::PortHandler *portHandler = dynamixel::PortHandler::getPortHandler(DEVICENAME);

  // Initialize PacketHandler instance
  // Set the protocol version
  // Get methods and members of Protocol1PacketHandler or Protocol2PacketHandler
  dynamixel::PacketHandler *packetHandler = dynamixel::PacketHandler::getPacketHandler(PROTOCOL_VERSION);

  // Initialize GroupSyncWrite instance
  dynamixel::GroupSyncWrite groupSyncWrite(portHandler, packetHandler, ADDR_MX_GOAL_POSITION, LEN_MX_GOAL_POSITION);

  int index = 0;
  int dxl_comm_result = COMM_TX_FAIL;             // Communication result
  bool dxl_addparam_result = false;                // addParam result
  int dxl_goal_position[2] = {DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE};         // Goal position

  uint8_t dxl_error = 0;                          // Dynamixel error
  uint8_t param_goal_position[2];
  uint16_t dxl1_present_position = 0, dxl2_present_position = 0;              // Present position

  // Open port
  if (portHandler->openPort())
  {
    printf("Succeeded to open the port!\n");
  }
  else
  {
    printf("Failed to open the port!\n");
    printf("Press any key to terminate...\n");
    getch();
    return 0;
  }

  // Set port baudrate
  if (portHandler->setBaudRate(BAUDRATE))
  {
    printf("Succeeded to change the baudrate!\n");
  }
  else
  {
    printf("Failed to change the baudrate!\n");
    printf("Press any key to terminate...\n");
    getch();
    return 0;
  }

  // Enable Dynamixel#1 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }
  else
  {
    printf("Dynamixel#%d has been successfully connected \n", DXL1_ID);
  }

  // Enable Dynamixel#2 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }
  else
  {
    printf("Dynamixel#%d has been successfully connected \n", DXL2_ID);
  }

  while(1)
  {
    printf("Press any key to continue! (or press ESC to quit!)\n");
    if (getch() == ESC_ASCII_VALUE)
      break;

    // Allocate goal position value into byte array
    param_goal_position[0] = DXL_LOBYTE(dxl_goal_position[index]);
    param_goal_position[1] = DXL_HIBYTE(dxl_goal_position[index]);

    // Add Dynamixel#1 goal position value to the Syncwrite storage
    dxl_addparam_result = groupSyncWrite.addParam(DXL1_ID, param_goal_position);
    if (dxl_addparam_result != true)
    {
      fprintf(stderr, "[ID:%03d] groupSyncWrite addparam failed", DXL1_ID);
      return 0;
    }

    // Add Dynamixel#2 goal position value to the Syncwrite parameter storage
    dxl_addparam_result = groupSyncWrite.addParam(DXL2_ID, param_goal_position);
    if (dxl_addparam_result != true)
    {
      fprintf(stderr, "[ID:%03d] groupSyncWrite addparam failed", DXL2_ID);
      return 0;
    }

    // Syncwrite goal position
    dxl_comm_result = groupSyncWrite.txPacket();
    if (dxl_comm_result != COMM_SUCCESS) packetHandler->printTxRxResult(dxl_comm_result);

    // Clear syncwrite parameter storage
    groupSyncWrite.clearParam();

    do
    {
      // Read Dynamixel#1 present position
      dxl_comm_result = packetHandler->read2ByteTxRx(portHandler, DXL1_ID, ADDR_MX_PRESENT_POSITION, &dxl1_present_position, &dxl_error);
      if (dxl_comm_result != COMM_SUCCESS)
      {
        packetHandler->printTxRxResult(dxl_comm_result);
      }
      else if (dxl_error != 0)
      {
        packetHandler->printRxPacketError(dxl_error);
      }

      // Read Dynamixel#2 present position
      dxl_comm_result = packetHandler->read2ByteTxRx(portHandler, DXL2_ID, ADDR_MX_PRESENT_POSITION, &dxl2_present_position, &dxl_error);
      if (dxl_comm_result != COMM_SUCCESS)
      {
        packetHandler->printTxRxResult(dxl_comm_result);
      }
      else if (dxl_error != 0)
      {
        packetHandler->printRxPacketError(dxl_error);
      }

      printf("[ID:%03d] GoalPos:%03d  PresPos:%03d\t[ID:%03d] GoalPos:%03d  PresPos:%03d\n", DXL1_ID, dxl_goal_position[index], dxl1_present_position, DXL2_ID, dxl_goal_position[index], dxl2_present_position);

    }while((abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD) || (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
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }

  // Disable Dynamixel#2 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }

  // Close port
  portHandler->closePort();

  return 0;
}

Details

#ifdef __linux__
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#elif defined(_WIN32) || defined(_WIN64)
#include <conio.h>
#endif

This source includes above to get key input interruption while the example is running. Actual functions for getting the input is described in a little below.

#include <stdlib.h>

The function abs() is in the example code, and it needs stdlib.h to be included.

#include <stdio.h>

The example shows Dynamixel status in sequence by the function printf(). So here stdio.h is needed.

#include "DynamixelSDK.h"                                   // Uses DYNAMIXEL SDK library

All libraries of DYNAMIXEL SDK are linked with the header file dynamixel_sdk.h.

// Control table address
#define ADDR_MX_TORQUE_ENABLE           24                  // Control table address is different in Dynamixel model
#define ADDR_MX_GOAL_POSITION           30
#define ADDR_MX_PRESENT_POSITION        36

// Data Byte Length
#define LEN_MX_GOAL_POSITION            2
#define LEN_MX_PRESENT_POSITION         2

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://emanual.robotis.com/.

// Protocol version
#define PROTOCOL_VERSION                1.0                 // 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
#define DXL1_ID                         1                   // Dynamixel#1 ID: 1
#define DXL2_ID                         2                   // Dynamixel#2 ID: 2
#define BAUDRATE                        1000000
#define DEVICENAME1                     "/dev/ttyUSB0"      // Check which port is being used on your controller

#define TORQUE_ENABLE                   1                   // Value for enabling the torque
#define TORQUE_DISABLE                  0                   // Value for disabling the torque
#define DXL_MINIMUM_POSITION_VALUE      100                 // Dynamixel will rotate between this value
#define DXL_MAXIMUM_POSITION_VALUE      4000                // 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.)
#define DXL_MOVING_STATUS_THRESHOLD     10                  // Dynamixel moving status threshold

#define ESC_ASCII_VALUE                 0x1b

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 DYNAMIXEL’s 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 getch()
{
#ifdef __linux__
  struct termios oldt, newt;
  int ch;
  tcgetattr(STDIN_FILENO, &oldt);
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  ch = getchar();
  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
  return ch;
#elif defined(_WIN32) || defined(_WIN64)
  return _getch();
#endif
}

int kbhit(void)
{
#ifdef __linux__
  struct termios oldt, newt;
  int ch;
  int oldf;

  tcgetattr(STDIN_FILENO, &oldt);
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  oldf = fcntl(STDIN_FILENO, F_GETFL, 0);
  fcntl(STDIN_FILENO, F_SETFL, oldf | O_NONBLOCK);

  ch = getchar();

  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
  fcntl(STDIN_FILENO, F_SETFL, oldf);

  if (ch != EOF)
  {
    ungetc(ch, stdin);
    return 1;
  }

  return 0;
#elif defined(_WIN32) || defined(_WIN64)
  return _kbhit();
#endif
}

These functions accept the key inputs in terms of example action. The example codes mainly apply the function getch() rather than the function kbhit() to get information which key has been pressed.

int main()
{
  // Initialize PortHandler instance
  // Set the port path
  // Get methods and members of PortHandlerLinux or PortHandlerWindows
  dynamixel::PortHandler *portHandler = dynamixel::PortHandler::getPortHandler(DEVICENAME);

  // Initialize PacketHandler instance
  // Set the protocol version
  // Get methods and members of Protocol1PacketHandler or Protocol2PacketHandler
  dynamixel::PacketHandler *packetHandler = dynamixel::PacketHandler::getPacketHandler(PROTOCOL_VERSION);

  // Initialize GroupSyncWrite instance
  dynamixel::GroupSyncWrite groupSyncWrite(portHandler, packetHandler, ADDR_MX_GOAL_POSITION, LEN_MX_GOAL_POSITION);

  int index = 0;
  int dxl_comm_result = COMM_TX_FAIL;             // Communication result
  bool dxl_addparam_result = false;                // addParam result
  int dxl_goal_position[2] = {DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE};         // Goal position

  uint8_t dxl_error = 0;                          // Dynamixel error
  uint8_t param_goal_position[2];
  uint16_t dxl1_present_position = 0, dxl2_present_position = 0;              // Present position

  // Open port
  if (portHandler->openPort())
  {
    printf("Succeeded to open the port!\n");
  }
  else
  {
    printf("Failed to open the port!\n");
    printf("Press any key to terminate...\n");
    getch();
    return 0;
  }

  // Set port baudrate
  if (portHandler->setBaudRate(BAUDRATE))
  {
    printf("Succeeded to change the baudrate!\n");
  }
  else
  {
    printf("Failed to change the baudrate!\n");
    printf("Press any key to terminate...\n");
    getch();
    return 0;
  }

  // Enable Dynamixel#1 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }
  else
  {
    printf("Dynamixel#%d has been successfully connected \n", DXL1_ID);
  }

  // Enable Dynamixel#2 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }
  else
  {
    printf("Dynamixel#%d has been successfully connected \n", DXL2_ID);
  }

  while(1)
  {
    printf("Press any key to continue! (or press ESC to quit!)\n");
    if (getch() == ESC_ASCII_VALUE)
      break;

    // Allocate goal position value into byte array
    param_goal_position[0] = DXL_LOBYTE(dxl_goal_position[index]);
    param_goal_position[1] = DXL_HIBYTE(dxl_goal_position[index]);

    // Add Dynamixel#1 goal position value to the Syncwrite storage
    dxl_addparam_result = groupSyncWrite.addParam(DXL1_ID, param_goal_position);
    if (dxl_addparam_result != true)
    {
      fprintf(stderr, "[ID:%03d] groupSyncWrite addparam failed", DXL1_ID);
      return 0;
    }

    // Add Dynamixel#2 goal position value to the Syncwrite parameter storage
    dxl_addparam_result = groupSyncWrite.addParam(DXL2_ID, param_goal_position);
    if (dxl_addparam_result != true)
    {
      fprintf(stderr, "[ID:%03d] groupSyncWrite addparam failed", DXL2_ID);
      return 0;
    }

    // Syncwrite goal position
    dxl_comm_result = groupSyncWrite.txPacket();
    if (dxl_comm_result != COMM_SUCCESS) packetHandler->printTxRxResult(dxl_comm_result);

    // Clear syncwrite parameter storage
    groupSyncWrite.clearParam();

    do
    {
      // Read Dynamixel#1 present position
      dxl_comm_result = packetHandler->read2ByteTxRx(portHandler, DXL1_ID, ADDR_MX_PRESENT_POSITION, &dxl1_present_position, &dxl_error);
      if (dxl_comm_result != COMM_SUCCESS)
      {
        packetHandler->printTxRxResult(dxl_comm_result);
      }
      else if (dxl_error != 0)
      {
        packetHandler->printRxPacketError(dxl_error);
      }

      // Read Dynamixel#2 present position
      dxl_comm_result = packetHandler->read2ByteTxRx(portHandler, DXL2_ID, ADDR_MX_PRESENT_POSITION, &dxl2_present_position, &dxl_error);
      if (dxl_comm_result != COMM_SUCCESS)
      {
        packetHandler->printTxRxResult(dxl_comm_result);
      }
      else if (dxl_error != 0)
      {
        packetHandler->printRxPacketError(dxl_error);
      }

      printf("[ID:%03d] GoalPos:%03d  PresPos:%03d\t[ID:%03d] GoalPos:%03d  PresPos:%03d\n", DXL1_ID, dxl_goal_position[index], dxl1_present_position, DXL2_ID, dxl_goal_position[index], dxl2_present_position);

    }while((abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD) || (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
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }

  // Disable Dynamixel#2 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }

  // Close port
  portHandler->closePort();

  return 0;
}

In main() function, the codes call actual functions for Dynamixel control.

  // Initialize PortHandler instance
  // Set the port path
  // Get methods and members of PortHandlerLinux or PortHandlerWindows
  dynamixel::PortHandler *portHandler = dynamixel::PortHandler::getPortHandler(DEVICENAME);

getPortHandler() function sets port path as DEVICENAME, and prepare an appropriate dynamixel::PortHandler in controller OS automatically.

  // Initialize PacketHandler instance
  // Set the protocol version
  // Get methods and members of Protocol1PacketHandler or Protocol2PacketHandler
  dynamixel::PacketHandler *packetHandler = dynamixel::PacketHandler::getPacketHandler(PROTOCOL_VERSION);

getPacketHandler() function sets the methods for packet construction by choosing the PROTOCOL_VERSION.

  // Initialize GroupSyncWrite instance
  dynamixel::GroupSyncWrite groupSyncWrite(portHandler, packetHandler, ADDR_MX_GOAL_POSITION, LEN_MX_GOAL_POSITION);

Methods of groupSyncWrite instance deals simultaneously with more than one Dynamixel through the port which the portHandler handles, building packets by the methods of packetHandler instance and writing LEN_MX_GOAL_POSITION bytes of the values on the address ADDR_MX_GOAL_POSITION.

  int index = 0;
  int dxl_comm_result = COMM_TX_FAIL;             // Communication result
  bool dxl_addparam_result = false;                // addParam result
  int dxl_goal_position[2] = {DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE};         // Goal position

  uint8_t dxl_error = 0;                          // Dynamixel error
  uint8_t param_goal_position[2];
  uint16_t 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_goal_position stores goal points of Dynamixel rotation.

dxl_error shows the internal error in Dynamixel.

param_goal_position becomes filled with couple of goal position values to write on each Dynamixel.

dxl1_present_position and dxl2_present_position view where now each Dynamixel points out.

  // Open port
  if (portHandler->openPort())
  {
    printf("Succeeded to open the port!\n");
  }
  else
  {
    printf("Failed to open the port!\n");
    printf("Press any key to terminate...\n");
    getch();
    return 0;
  }

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

  // Set port baudrate
  if (portHandler->setBaudRate(BAUDRATE))
  {
    printf("Succeeded to change the baudrate!\n");
  }
  else
  {
    printf("Failed to change the baudrate!\n");
    printf("Press any key to terminate...\n");
    getch();
    return 0;
  }

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

  // Enable Dynamixel#1 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }
  else
  {
    printf("Dynamixel#%d has been successfully connected \n", DXL1_ID);
  }

  // Enable Dynamixel#2 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }
  else
  {
    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.

dynamixel::PacketHandler::write1ByteTxRx() function sends an instruction to the #DXL_ID Dynamixel through the port which the portHandler handles, writing 1 byte of TORQUE_ENABLE value to ADDR_MX_TORQUE_ENABLE address. Then, it receives the dxl_error. The function returns 0 if no communication error has been occurred.

  while(1)
  {
    printf("Press any key to continue! (or press ESC to quit!)\n");
    if (getch() == ESC_ASCII_VALUE)
      break;

    // Allocate goal position value into byte array
    param_goal_position[0] = DXL_LOBYTE(dxl_goal_position[index]);
    param_goal_position[1] = DXL_HIBYTE(dxl_goal_position[index]);

    // Add Dynamixel#1 goal position value to the Syncwrite storage
    dxl_addparam_result = groupSyncWrite.addParam(DXL1_ID, param_goal_position);
    if (dxl_addparam_result != true)
    {
      fprintf(stderr, "[ID:%03d] groupSyncWrite addparam failed", DXL1_ID);
      return 0;
    }

    // Add Dynamixel#2 goal position value to the Syncwrite parameter storage
    dxl_addparam_result = groupSyncWrite.addParam(DXL2_ID, param_goal_position);
    if (dxl_addparam_result != true)
    {
      fprintf(stderr, "[ID:%03d] groupSyncWrite addparam failed", DXL2_ID);
      return 0;
    }

    // Syncwrite goal position
    dxl_comm_result = groupSyncWrite.txPacket();
    if (dxl_comm_result != COMM_SUCCESS) packetHandler->printTxRxResult(dxl_comm_result);

    // Clear syncwrite parameter storage
    groupSyncWrite.clearParam();

    do
    {
      // Read Dynamixel#1 present position
      dxl_comm_result = packetHandler->read2ByteTxRx(portHandler, DXL1_ID, ADDR_MX_PRESENT_POSITION, &dxl1_present_position, &dxl_error);
      if (dxl_comm_result != COMM_SUCCESS)
      {
        packetHandler->printTxRxResult(dxl_comm_result);
      }
      else if (dxl_error != 0)
      {
        packetHandler->printRxPacketError(dxl_error);
      }

      // Read Dynamixel#2 present position
      dxl_comm_result = packetHandler->read2ByteTxRx(portHandler, DXL2_ID, ADDR_MX_PRESENT_POSITION, &dxl2_present_position, &dxl_error);
      if (dxl_comm_result != COMM_SUCCESS)
      {
        packetHandler->printTxRxResult(dxl_comm_result);
      }
      else if (dxl_error != 0)
      {
        packetHandler->printRxPacketError(dxl_error);
      }

      printf("[ID:%03d] GoalPos:%03d  PresPos:%03d\t[ID:%03d] GoalPos:%03d  PresPos:%03d\n", DXL1_ID, dxl_goal_position[index], dxl1_present_position, DXL2_ID, dxl_goal_position[index], dxl2_present_position);

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

param_goal_position[0] and param_goal_position[1] becomes filled with each low-byte and high-byte part of dxl_goal_position by using predefined function DXL_LOBYTE() and DXL_HIBYTE().

dynamixel::GroupSyncWrite::addParam() function stores the Dynamixel ID and its goal position param_goal_position to the syncwrite target Dynamixel list.

dynamixel::GroupSyncWrite::txPacket() function sends an instruction to the Dynamixel #DXL1_ID and #DXL2_ID at the same time through the ports which the portHandler handles, making it possible to write same pre-listed length bytes to same pre-listed address. The function returns 0 if no communication error has been occurred.

dynamixel::GroupSyncWrite::clearParam() function clears the Dynamixel list of groupsyncwrite.

dynamixel::PacketHandler::read2ByteTxRx() functions order to the Dynamixel #DXL1_ID and #DXL2_ID through the port which the portHandler handles, requesting 2 bytes of values of ADDR_MX_PRESENT_POSITION address. Then, they receive dxl_present_positions and dxl_errors. The functions return 0 if no communication error has been occurred.

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
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }

  // Disable Dynamixel#2 Torque
  dxl_comm_result = packetHandler->write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE, &dxl_error);
  if (dxl_comm_result != COMM_SUCCESS)
  {
    packetHandler->printTxRxResult(dxl_comm_result);
  }
  else if (dxl_error != 0)
  {
    packetHandler->printRxPacketError(dxl_error);
  }

The controller frees the DYNAMIXEL to be idle.

dynamixel::PacketHandler::write1ByteTxRx() function sends an instruction to the #DXL_ID Dynamixel through the port which the portHandler handles, writing 1 byte of TORQUE_DISABLE value to ADDR_MX_TORQUE_ENABLE address. Then, it receives the dxl_error. The function returns 0 if no communication error has been occurred.

    // Close port
    portHandler->closePort();

    return 0;

Finally, port becomes disposed.