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Python Sync Read Write Protocol 2.0

Sample code

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

#
# sync_read_write.py
#
#  Created on: 2016. 6. 16.
#      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 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_GOAL_POSITION      = 596
ADDR_PRO_PRESENT_POSITION   = 611

# Data Byte Length
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 Groupsyncwrite instance
groupwrite_num = dynamixel.groupSyncWrite(port_num, PROTOCOL_VERSION, ADDR_PRO_GOAL_POSITION, LEN_PRO_GOAL_POSITION)

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

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
dxl1_present_position = 0                                   # Present position
dxl2_present_position = 0

# 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.groupSyncReadAddParam(groupread_num, DXL1_ID)).value
if dxl_addparam_result != 1:
    print("[ID:%03d] groupSyncRead addparam failed" % (DXL1_ID))
    quit()

# Add parameter storage for Dynamixel#2 present position value
dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupSyncReadAddParam(groupread_num, DXL2_ID)).value
if dxl_addparam_result != 1:
    print("[ID:%03d] groupSyncRead 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 Dynamixel#1 goal position value to the Syncwrite storage
    dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupSyncWriteAddParam(groupwrite_num, DXL1_ID, dxl_goal_position[index], LEN_PRO_GOAL_POSITION)).value
    print(dxl_addparam_result)
    if dxl_addparam_result != 1:
        print("[ID:%03d] groupSyncWrite addparam failed" % (DXL1_ID))
        quit()

    # Add Dynamixel#2 goal position value to the Syncwrite parameter storage
    dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupSyncWriteAddParam(groupwrite_num, DXL2_ID, dxl_goal_position[index], LEN_PRO_GOAL_POSITION)).value
    if dxl_addparam_result != 1:
        print("[ID:%03d] groupSyncWrite addparam failed" % (DXL2_ID))
        quit()

    # Syncwrite goal position
    dynamixel.groupSyncWriteTxPacket(groupwrite_num)
    if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
        dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))

    # Clear syncwrite parameter storage
    dynamixel.groupSyncWriteClearParam(groupwrite_num)

    while 1:
        # Syncread present position
        dynamixel.groupSyncReadTxRxPacket(groupread_num)
        if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
            dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))

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

        # Check if groupsyncread data of Dynamixel#2 is available
        dxl_getdata_result = ctypes.c_ubyte(dynamixel.groupSyncReadIsAvailable(groupread_num, DXL2_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION)).value
        if dxl_getdata_result != 1:
            print("[ID:%03d] groupSyncRead getdata failed" % (DXL2_ID))
            quit()

        # 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)

        print("[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))

        if not ((abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD) or (abs(dxl_goal_position[index] - dxl2_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_GOAL_POSITION      = 596
ADDR_PRO_PRESENT_POSITION   = 611

# Data Byte Length
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.

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 Groupsyncwrite instance
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
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.

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
dxl1_present_position = 0                                   # Present position
dxl2_present_position = 0

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):
    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.groupSyncReadAddParam(groupread_num, DXL1_ID)).value
if dxl_addparam_result != 1:
    print("[ID:%03d] groupSyncRead addparam failed" % (DXL1_ID))
    quit()

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

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

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

    # Add Dynamixel#1 goal position value to the Syncwrite storage
    dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupSyncWriteAddParam(groupwrite_num, DXL1_ID, dxl_goal_position[index], LEN_PRO_GOAL_POSITION)).value
    print(dxl_addparam_result)
    if dxl_addparam_result != 1:
        print("[ID:%03d] groupSyncWrite addparam failed" % (DXL1_ID))
        quit()

    # Add Dynamixel#2 goal position value to the Syncwrite parameter storage
    dxl_addparam_result = ctypes.c_ubyte(dynamixel.groupSyncWriteAddParam(groupwrite_num, DXL2_ID, dxl_goal_position[index], LEN_PRO_GOAL_POSITION)).value
    if dxl_addparam_result != 1:
        print("[ID:%03d] groupSyncWrite addparam failed" % (DXL2_ID))
        quit()

    # Syncwrite goal position
    dynamixel.groupSyncWriteTxPacket(groupwrite_num)
    if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
        dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))

    # Clear syncwrite parameter storage
    dynamixel.groupSyncWriteClearParam(groupwrite_num)

    while 1:
        # Syncread present position
        dynamixel.groupSyncReadTxRxPacket(groupread_num)
        if dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION) != COMM_SUCCESS:
            dynamixel.printTxRxResult(PROTOCOL_VERSION, dynamixel.getLastTxRxResult(port_num, PROTOCOL_VERSION))

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

        # Check if groupsyncread data of Dynamixel#2 is available
        dxl_getdata_result = ctypes.c_ubyte(dynamixel.groupSyncReadIsAvailable(groupread_num, DXL2_ID, ADDR_PRO_PRESENT_POSITION, LEN_PRO_PRESENT_POSITION)).value
        if dxl_getdata_result != 1:
            print("[ID:%03d] groupSyncRead getdata failed" % (DXL2_ID))
            quit()

        # 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)

        print("[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))

        if not ((abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD) or (abs(dxl_goal_position[index] - dxl2_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 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 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.