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Java Read Write Protocol 2.0

Sample code

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

//
// *********     Read and Write Example      *********
//
//
// Available Dynamixel model on this example : All models using Protocol 2.0
// This example is designed for using a 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 ReadWrite
{
  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;

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

    // Default setting
    byte DXL_ID                         = 1;                   // Dynamixel ID: 1
    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();

    int index = 0;
    int dxl_comm_result = COMM_TX_FAIL;                        // Communication result
    int[] dxl_goal_position = new int[]{DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE};         // Goal position

    byte dxl_error = 0;                                        // Dynamixel error
    int dxl_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 Torque
    dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL_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.println("Dynamixel has been successfully connected");
    }

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

      // Write goal position
      dynamixel.write4ByteTxRx(port_num, PROTOCOL_VERSION, DXL_ID, ADDR_PRO_GOAL_POSITION, dxl_goal_position[index]);
      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);
      }

      do
      {
        // Read present position
        dxl_present_position = dynamixel.read4ByteTxRx(port_num, PROTOCOL_VERSION, DXL_ID, ADDR_PRO_PRESENT_POSITION);
        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);
        }

        System.out.printf("[ID: %d] GoalPos:%d  PresPos:%d\n", DXL_ID, dxl_goal_position[index], dxl_present_position);

      } while ((Math.abs(dxl_goal_position[index] - dxl_present_position) > DXL_MOVING_STATUS_THRESHOLD));

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

    // Disable Dynamixel Torque
    dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL_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;
  }
}

Details

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;

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
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 DXL_ID                         = 1;                   // Dynamixel ID: 1
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 already 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.

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.

int index = 0;
int dxl_comm_result = COMM_TX_FAIL;                        // Communication result
int[] dxl_goal_position = new int[]{DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE};         // Goal position

byte dxl_error = 0;                                        // Dynamixel error
int dxl_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_goal_position stores goal points of Dynamixel rotation.

dxl_error shows the internal error in Dynamixel.

dxl_present_position views where now it 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 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL_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.println("Dynamixel has been successfully connected");
}

As mentioned in the document, above code enables Dynamixel torque to set its status as being ready to move.

write1ByteTxRx() function sends an instruction to the #DXL_ID Dynamixel 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.

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

  // Write goal position
  dynamixel.write4ByteTxRx(port_num, PROTOCOL_VERSION, DXL_ID, ADDR_PRO_GOAL_POSITION, dxl_goal_position[index]);
  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);
  }

  do
  {
    // Read present position
    dxl_present_position = dynamixel.read4ByteTxRx(port_num, PROTOCOL_VERSION, DXL_ID, ADDR_PRO_PRESENT_POSITION);
    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);
    }

    System.out.printf("[ID: %d] GoalPos:%d  PresPos:%d\n", DXL_ID, dxl_goal_position[index], dxl_present_position);

  } while ((Math.abs(dxl_goal_position[index] - dxl_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 the Dynamixel position through packet transmission/reception(Tx/Rx).

To continue its rotation, press any key except ESC.

write4ByteTxRx() function sends an instruction to the #DXL_ID Dynamixel in PROTOCOL_VERSION communication protocol through #port_num port, writing 4 byte of dxl_goal_position[index] value to ADDR_PRO_GOAL_POSITION 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.

read4ByteTxRx() function sends an instruction to the #DXL_ID Dynamixel in PROTOCOL_VERSION communication protocol through #port_num port, requesting 4 bytes of value in ADDR_PRO_PRESENT_POSITION 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.

Reading its present position will be ended when absolute value of (dxl_goal_position[index] - dxl_present_position) becomes smaller then DXL_MOVING_STATUS_THRESHOLD.

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

// Disable Dynamixel Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL_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 Dynamixel to be idle.

write1ByteTxRx() function sends an instruction to the #DXL_ID Dynamixel 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.