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Python Bulk Read Write Protocol 2.0

Sample code

#!/usr/bin/env python
# -*- coding: utf-8 -*-

#
# bulk_read_write.py
#
#  Created on: 2016. 6. 16.
#      Author: Ryu Woon Jung (Leon)
#

#
# *********     Bulk Read and Bulk 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 and 2 / Baudnum : 3 (Baudrate : 1000000 [1M])
#

import os, sys, ctypes

if os.name == 'nt':
    import msvcrt
    def getch():
        return msvcrt.getch().decode()
else:
    import tty, termios
    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)
    tty.setraw(sys.stdin.fileno())
    def getch():
        return sys.stdin.read(1)

os.sys.path.append('../dynamixel_functions_py')             # Path setting

import dynamixel_functions as dynamixel                     # Uses Dynamixel SDK library

# Control table address
ADDR_PRO_TORQUE_ENABLE      = 562                           # Control table address is different in Dynamixel model
ADDR_PRO_LED_RED            = 563
ADDR_PRO_GOAL_POSITION      = 596
ADDR_PRO_PRESENT_POSITION   = 611

# Data Byte Length
LEN_PRO_LED_RED             = 1
LEN_PRO_GOAL_POSITION       = 4
LEN_PRO_PRESENT_POSITION    = 4

# Protocol version
PROTOCOL_VERSION            = 2                             # See which protocol version is used in the Dynamixel

# Default setting
DXL1_ID                     = 1                             # Dynamixel ID: 1
DXL2_ID                     = 2                             # Dynamixel ID: 2
BAUDRATE                    = 1000000
DEVICENAME                  = "/dev/ttyUSB0".encode('utf-8')        # Check which port is being used on your controller
                                                            # ex) Windows: "COM1"   Linux: "/dev/ttyUSB0"

TORQUE_ENABLE               = 1                             # Value for enabling the torque
TORQUE_DISABLE              = 0                             # Value for disabling the torque
DXL_MINIMUM_POSITION_VALUE  = -150000                       # Dynamixel will rotate between this value
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.)
DXL_MOVING_STATUS_THRESHOLD = 20                            # Dynamixel moving status threshold

ESC_ASCII_VALUE             = 0x1b

COMM_SUCCESS                = 0                             # Communication Success result value
COMM_TX_FAIL                = -1001                         # Communication Tx Failed

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

# Initialize PacketHandler Structs
dynamixel.packetHandler()

# Initialize groupBulkWrite Struct
groupwrite_num = dynamixel.groupBulkWrite(port_num, PROTOCOL_VERSION)

# Initialize Groupsyncwrite instance
groupread_num = dynamixel.groupBulkRead(port_num, PROTOCOL_VERSION)

index = 0
dxl_comm_result = COMM_TX_FAIL                              # Communication result
dxl_addparam_result = 0                                     # AddParam result
dxl_getdata_result = 0                                      # GetParam result
dxl_goal_position = [DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE]         # Goal position

dxl_error = 0                                               # Dynamixel error
dxl_led_value = [0, 255]                                    # Dynamixel LED value for write
dxl1_present_position = 0                                   # Present position
dxl2_led_value_read = 0                                     # Dynamixel moving status


# Open port
if dynamixel.openPort(port_num):
    print("Succeeded to open the port!")
else:
    print("Failed to open the port!")
    print("Press any key to terminate...")
    getch()
    quit()

# Set port baudrate
if dynamixel.setBaudRate(port_num, BAUDRATE):
    print("Succeeded to change the baudrate!")
else:
    print("Failed to change the baudrate!")
    print("Press any key to terminate...")
    getch()
    quit()


# Enable Dynamixel#1 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL1_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_ENABLE)
if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))
elif dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION) != 0:
    dynamixel.printRxPacketError(PROTOCOL_VERSION, dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION))
else:
    print("Dynamixel#1 has been successfully connected")

# Enable Dynamixel#2 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL2_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_ENABLE)
if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))
elif dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION) != 0:
    dynamixel.printRxPacketError(PROTOCOL_VERSION, dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION))
else:
    print("Dynamixel#2 has been successfully connected")

# Add parameter storage for Dynamixel#1 present position value
dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupBulkReadAddParam(groupread_num, DXL1_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION)).value
if dxl_addparam_result != 1:
    print("[ID:%03d] groupBulkRead addparam failed" % (DXL1_ID))
    quit()

# Add parameter storage for Dynamixel#2 present moving value
dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupBulkReadAddParam(groupread_num, DXL2_ID, ADDR_PRO_LED_RED, LEN_PRO_LED_RED)).value
if dxl_addparam_result != 1:
    print("[ID:%03d] groupBulkRead addparam failed" % (DXL2_ID))
    quit()


while 1:
    print("Press any key to continue! (or press ESC to quit!)")
    if getch() == chr(ESC_ASCII_VALUE):
        break

    # Add parameter storage for Dynamixel#1 goal position
    dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupBulkWriteAddParam(groupwrite_num, DXL1_ID, ADDR_PRO_GOAL_POSITION, LEN_PRO_GOAL_POSITION, dxl_goal_position[index], LEN_PRO_GOAL_POSITION)).value
    if dxl_addparam_result != 1:
        fprintf(stderr, "[ID:%03d] groupBulkWrite addparam failed", DXL1_ID)
        quit()

    # Add parameter storage for Dynamixel#2 LED value
    dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupBulkWriteAddParam(groupwrite_num, DXL2_ID, ADDR_PRO_LED_RED, LEN_PRO_LED_RED, dxl_led_value[index], LEN_PRO_LED_RED)).value
    if dxl_addparam_result != 1:
        fprintf(stderr, "[ID:%03d] groupBulkWrite addparam failed", DXL2_ID)
        quit()

    # Bulkwrite goal position and LED value
    dynamixel.groupBulkWriteTxPacket(groupwrite_num)
    if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
        dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))

    # Clear bulkwrite parameter storage
    dynamixel.groupBulkWriteClearParam(groupwrite_num)

    while 1:
        # Bulkread present position and moving status
        dynamixel.groupBulkReadTxRxPacket(groupread_num)
        if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
            dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))

        # Check if groupbulkread data of Dynamixel#1 is available
        dxl_getdata_result = ctypes.c_ubyte(dynamixel.groupBulkReadIsAvailable(groupread_num, DXL1_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION)).value
        if dxl_getdata_result != 1:
            print("[ID:%03d] groupBulkRead getdata failed" % (DXL1_ID))
            quit()

        # Check if groupbulkread data of Dynamixel#2 is available
        dxl_getdata_result = ctypes.c_ubyte(dynamixel.groupBulkReadIsAvailable(groupread_num, DXL2_ID, ADDR_PRO_LED_RED, LEN_PRO_LED_RED)).value
        if dxl_getdata_result != 1:
            print("[ID:%03d] groupBulkRead getdata failed" % (DXL2_ID))
            quit()

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

        # Get Dynamixel#2 moving status value
        dxl2_led_value_read = dynamixel.groupBulkReadGetData(groupread_num, DXL2_ID, ADDR_PRO_LED_RED, LEN_PRO_LED_RED)

        print("[ID:%03d] Present Position : %d \t [ID:%03d] LED Value: %d" % (DXL1_ID, dxl1_present_position, DXL2_ID, dxl2_led_value_read))

        if not (abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD):
            break

    # 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 dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))
elif dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION) != 0:
    dynamixel.printRxPacketError(PROTOCOL_VERSION, dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION))

# Disable Dynamixel#2 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL2_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_DISABLE)
if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))
elif dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION) != 0:
    dynamixel.printRxPacketError(PROTOCOL_VERSION, dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION))

# Close port
dynamixel.closePort(port_num)

Details

import os, sys, ctypes

if os.name == 'nt':
    import msvcrt
    def getch():
        return msvcrt.getch().decode()
else:
    import tty, termios
    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)
    tty.setraw(sys.stdin.fileno())
    def getch():
        return sys.stdin.read(1)

os.sys.path.append('../dynamixel_functions_py')             # Path setting

import dynamixel_functions as dynamixel                     # Uses Dynamixel SDK library

getch() gets the input which is for example code control.

os.sys.path.append() sets paths of function reference.

This example uses dynamixel_functions library as dynamixel imported from dynamixel_functions_py package.

# Control table address
ADDR_PRO_TORQUE_ENABLE      = 562                           # Control table address is different in Dynamixel model
ADDR_PRO_LED_RED            = 563
ADDR_PRO_GOAL_POSITION      = 596
ADDR_PRO_PRESENT_POSITION   = 611

# Data Byte Length
LEN_PRO_LED_RED             = 1
LEN_PRO_GOAL_POSITION       = 4
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://emanual.robotis.com/.

# Protocol version
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
DXL1_ID                     = 1                             # Dynamixel ID: 1
DXL2_ID                     = 2                             # Dynamixel ID: 2
BAUDRATE                    = 1000000
DEVICENAME                  = "/dev/ttyUSB0".encode('utf-8')        # Check which port is being used on your controller
                                                            # ex) Windows: "COM1"   Linux: "/dev/ttyUSB0"

TORQUE_ENABLE               = 1                             # Value for enabling the torque
TORQUE_DISABLE              = 0                             # Value for disabling the torque
DXL_MINIMUM_POSITION_VALUE  = -150000                       # Dynamixel will rotate between this value
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.)
DXL_MOVING_STATUS_THRESHOLD = 20                            # Dynamixel moving status threshold

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 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.

Dynamixel LED has its own range of value: 1 byte red LED for Dynamixel MX-28 and 1byte each on red, green, blue LED for Dynamixel PRO 54-200.

DXL_MOVING_STATUS_THRESHOLD acts as a criteria for verifying its rotation stopped.

COMM_SUCCESS                = 0                             # Communication Success result value
COMM_TX_FAIL                = -1001                         # Communication Tx Failed

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

# Initialize PortHandler Structs
# Set the port path
# Get methods and members of PortHandlerLinux or PortHandlerWindows
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 groupBulkWrite Struct
groupwrite_num = dynamixel.groupBulkWrite(port_num, PROTOCOL_VERSION)

groupBulkWrite() function initializes grouped parameters used for packet construction and packet storing. The utility functions of bulk read deals simultaneously with more than one Dynamixel through #port_num port, building packets by the function which uses PROTOCOL_VERSION.

# Initialize Groupsyncwrite instance
groupread_num = dynamixel.groupBulkRead(port_num, PROTOCOL_VERSION)

groupBulkRead() function initializes grouped parameters used for packet construction and packet storing. The utility functions of bulk read deals simultaneously with more than one Dynamixel through #port_num port, building packets by the function which uses PROTOCOL_VERSION.

index = 0
dxl_comm_result = COMM_TX_FAIL                              # Communication result
dxl_addparam_result = 0                                     # AddParam result
dxl_getdata_result = 0                                      # GetParam result
dxl_goal_position = [DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE]         # Goal position

dxl_error = 0                                               # Dynamixel error
dxl_led_value = [0, 255]                                    # Dynamixel LED value for write
dxl1_present_position = 0                                   # Present position
dxl2_led_value_read = 0                                     # Dynamixel moving status

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.

dxl_led_value stores LED values of Dynamixel.

dxl1_present_position views where now Dynamixel DXL1_ID points out.

dxl2_moving views whether the Dynamixel is stopped.

# Open port
if dynamixel.openPort(port_num):
    print("Succeeded to open the port!")
else:
    print("Failed to open the port!")
    print("Press any key to terminate...")
    getch()
    quit()

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):
    print("Succeeded to change the baudrate!")
else:
    print("Failed to change the baudrate!")
    print("Press any key to terminate...")
    getch()
    quit()

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 dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))
elif dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION) != 0:
    dynamixel.printRxPacketError(PROTOCOL_VERSION, dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION))
else:
    print("Dynamixel#1 has been successfully connected")

# Enable Dynamixel#2 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL2_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_ENABLE)
if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))
elif dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION) != 0:
    dynamixel.printRxPacketError(PROTOCOL_VERSION, dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION))
else:
    print("Dynamixel#2 has been successfully connected")

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 = ctypes.c_ubyte(dynamixel.groupBulkReadAddParam(groupread_num, DXL1_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION)).value
if dxl_addparam_result != 1:
    print("[ID:%03d] groupBulkRead addparam failed" % (DXL1_ID))
    quit()

# Add parameter storage for Dynamixel#2 present moving value
dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupBulkReadAddParam(groupread_num, DXL2_ID, ADDR_PRO_LED_RED, LEN_PRO_LED_RED)).value
if dxl_addparam_result != 1:
    print("[ID:%03d] groupBulkRead addparam failed" % (DXL2_ID))
    quit()

groupBulkReadAddParam() function stores the Dynamixel ID and address ADDR_PRO_PRESENT_POSITION or ADDR_PRO_LED_RED, byte length LEN_PRO_PRESENT_POSITION or LEN_PRO_LED_RED of required data to the bulkread target Dynamixel list.

while 1:
    print("Press any key to continue! (or press ESC to quit!)")
    if getch() == chr(ESC_ASCII_VALUE):
        break

    # Add parameter storage for Dynamixel#1 goal position
    dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupBulkWriteAddParam(groupwrite_num, DXL1_ID, ADDR_PRO_GOAL_POSITION, LEN_PRO_GOAL_POSITION, dxl_goal_position[index], LEN_PRO_GOAL_POSITION)).value
    if dxl_addparam_result != 1:
        fprintf(stderr, "[ID:%03d] groupBulkWrite addparam failed", DXL1_ID)
        quit()

    # Add parameter storage for Dynamixel#2 LED value
    dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupBulkWriteAddParam(groupwrite_num, DXL2_ID, ADDR_PRO_LED_RED, LEN_PRO_LED_RED, dxl_led_value[index], LEN_PRO_LED_RED)).value
    if dxl_addparam_result != 1:
        fprintf(stderr, "[ID:%03d] groupBulkWrite addparam failed", DXL2_ID)
        quit()

    # Bulkwrite goal position and LED value
    dynamixel.groupBulkWriteTxPacket(groupwrite_num)
    if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
        dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))

    # Clear bulkwrite parameter storage
    dynamixel.groupBulkWriteClearParam(groupwrite_num)

    while 1:
        # Bulkread present position and moving status
        dynamixel.groupBulkReadTxRxPacket(groupread_num)
        if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
            dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))

        # Check if groupbulkread data of Dynamixel#1 is available
        dxl_getdata_result = ctypes.c_ubyte(dynamixel.groupBulkReadIsAvailable(groupread_num, DXL1_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION)).value
        if dxl_getdata_result != 1:
            print("[ID:%03d] groupBulkRead getdata failed" % (DXL1_ID))
            quit()

        # Check if groupbulkread data of Dynamixel#2 is available
        dxl_getdata_result = ctypes.c_ubyte(dynamixel.groupBulkReadIsAvailable(groupread_num, DXL2_ID, ADDR_PRO_LED_RED, LEN_PRO_LED_RED)).value
        if dxl_getdata_result != 1:
            print("[ID:%03d] groupBulkRead getdata failed" % (DXL2_ID))
            quit()

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

        # Get Dynamixel#2 moving status value
        dxl2_led_value_read = dynamixel.groupBulkReadGetData(groupread_num, DXL2_ID, ADDR_PRO_LED_RED, LEN_PRO_LED_RED)

        print("[ID:%03d] Present Position : %d \t [ID:%03d] LED Value: %d" % (DXL1_ID, dxl1_present_position, DXL2_ID, dxl2_led_value_read))

        if not (abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD):
            break

    # Change goal position
    if index == 0:
        index = 1
    else:
        index = 0

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

To continue their rotation, press any key except ESC.

groupBulkWriteAddParam() function stores the Dynamixel ID and its goal position dxl_goal_position or red LED value dxl_led_value to the bulkwrite target Dynamixel list.

groupBulkWriteTxPacket() function orders to the Dynamixel #DXL1_ID and #DXL2_ID at the same time through the port, making it possible to write data bytes to different address. (In this example, LEN_PRO_GOAL_POSITION bytes of the values to the address ADDR_PRO_GOAL_POSITION and LEN_PRO_LED_RED bytes of the values to the address ADDR_PRO_LED_RED, each.) 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.

groupBulkWriteClearParam() function clears the Dynamixel list of groupbulkwrite.

groupBulkReadTxRxPacket() function orders to the Dynamixel #DXL1_ID and #DXL2_ID at the same time through the port, making it possible to require data bytes from different address. (In this example, LEN_PRO_PRESENT_POSITION bytes of the values to the address ADDR_PRO_PRESENT_POSITION and LEN_PRO_LED_RED bytes of the values to the address ADDR_PRO_LED_RED, each.) 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.

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

groupBulkReadGetData() function pop the data received by groupBulkReadTxRxPacket() function out. In the example, it stores LEN_PRO_PRESENT_POSITION byte data got from ADDR_PRO_PRESENT_POSITION address of DXL1_ID Dynamixel and LEN_PRO_LED_RED byte data got from ADDR_PRO_LED_RED address of DXL2_ID Dynamixel, each.

groupBulkReadClearParam() function clears the Dynamixel list of groupbulkread.

Reading their present position will be ended when absolute value of (dxl_goal_position[index] - dxl1_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 dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))
elif dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION) != 0:
    dynamixel.printRxPacketError(PROTOCOL_VERSION, dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION))

# Disable Dynamixel#2 Torque
dynamixel.write1ByteTxRx(port_num, PROTOCOL_VERSION, DXL2_ID, ADDR_PRO_TORQUE_ENABLE, TORQUE_DISABLE)
if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
    dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))
elif dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION) != 0:
    dynamixel.printRxPacketError(PROTOCOL_VERSION, dynamixel.getLastRxPacketError(port_num, PROTOCOL_VERSION))

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)

Finally, port becomes disposed.