arbotix.py

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#!/usr/bin/env python

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# Author: Michael Ferguson

## @file arbotix.py Low-level code to control an ArbotiX.

import serial, time, sys, thread
from ax12 import *
from struct import unpack

## @brief ArbotiX errors. Used by now to handle broken serial connections.
class ArbotiXException(Exception):
    pass

## @brief This class controls an ArbotiX, USBDynamixel, or similar board through a serial connection.
class ArbotiX:

    ## @brief Constructs an ArbotiX instance, optionally opening the serial connection.
    
    def __init__(self, port="/dev/ttyUSB0", baud=115200, timeout=0.1, open_port=True):
        self._mutex = thread.allocate_lock()
        self._ser = serial.Serial()
        
        self._ser.port = port
        self._ser.baudrate = baud
        self._ser.timeout = timeout

        if open_port:
            self._ser.open()

        ## The last error level read back
        self.error = 0

    def __write__(self, msg):
        try:
            self._ser.write(msg)
        except serial.SerialException as e:
            self._mutex.release()
            raise ArbotiXException(e)

    def openPort(self):
        self._ser.close()
        try:
            self._ser.open()
        except serial.SerialException as e:
            raise ArbotiXException(e)

    def closePort(self):
        self._ser.close()

    ## @brief Read a dynamixel return packet in an iterative attempt.
    
    def getPacket(self, mode, id=-1, leng=-1, error=-1, params = None):
        try:
            d = self._ser.read()     
        except Exception as e:
            print e
            return None
        # need a positive byte
        if d == '':
            return None

        # now process our byte
        if mode == 0:           # get our first 0xFF
            if ord(d) == 0xff:   
                return self.getPacket(1)
            else:
                return self.getPacket(0)
        elif mode == 1:         # get our second 0xFF
            if ord(d) == 0xff:
                return self.getPacket(2)
            else:
                return self.getPacket(0)
        elif mode == 2:         # get id
            if d != 0xff:
                return self.getPacket(3, ord(d))
            else:              
                return self.getPacket(0)
        elif mode == 3:         # get length
            return self.getPacket(4, id, ord(d))
        elif mode == 4:         # read error    
            self.error = ord(d)
            if leng == 2:
                return self.getPacket(6, id, leng, ord(d), list())
            else:
                return self.getPacket(5, id, leng, ord(d), list())
        elif mode == 5:         # read params
            params.append(ord(d))
            if len(params) + 2 == leng:
                return self.getPacket(6, id, leng, error, params)
            else:
                return self.getPacket(5, id, leng, error, params)
        elif mode == 6:         # read checksum
            checksum = id + leng + error + sum(params) + ord(d)
            if checksum % 256 != 255:
                return None
            return params
        # fail
        return None

    ## @brief Send an instruction to the device. 
    
    def execute(self, index, ins, params, ret=True):
        values = None
        self._mutex.acquire()  
        try:      
            self._ser.flushInput()
        except Exception as e:
            print e
        length = 2 + len(params)
        checksum = 255 - ((index + length + ins + sum(params))%256)
        self.__write__(chr(0xFF)+chr(0xFF)+chr(index)+chr(length)+chr(ins))
        for val in params:
            self.__write__(chr(val))
        self.__write__(chr(checksum))
        if ret:
            values = self.getPacket(0)
        self._mutex.release()
        return values
    
    ## @brief Read values of registers.
    
    def read(self, index, start, length):
        values = self.execute(index, AX_READ_DATA, [start, length])
        if values == None:
            return -1        
        else:
            return values

    ## @brief Write values to registers.
    
    def write(self, index, start, values):
        self.execute(index, AX_WRITE_DATA, [start] + values)
        return self.error     

    ## @brief Write values to registers on many servos.
    
    def syncWrite(self, start, values):
        output = list()
        for i in values:
            output = output + i 
        length = len(output) + 4                # length of overall packet
        lbytes = len(values[0])-1               # length of bytes to write to a servo               
        self._mutex.acquire()  
        try:      
            self._ser.flushInput()
        except:
            pass  
        self.__write__(chr(0xFF)+chr(0xFF)+chr(254)+chr(length)+chr(AX_SYNC_WRITE))
        self.__write__(chr(start))              # start address
        self.__write__(chr(lbytes))             # bytes to write each servo
        for i in output:
            self.__write__(chr(i))
        checksum = 255 - ((254 + length + AX_SYNC_WRITE + start + lbytes + sum(output))%256)
        self.__write__(chr(checksum))
        self._mutex.release()

    ## @brief Read values of registers on many servos.
    
    def syncRead(self, servos, start, length):
        return self.execute(0xFE, AX_SYNC_READ, [start, length] + servos )
    
    ## @brief Set baud rate of a device.
    
    def setBaud(self, index, baud):
        return self.write(index, P_BAUD_RATE, [baud, ])

    ## @brief Get the return level of a device.
    
    def getReturnLevel(self, index):
        try:
            return int(self.read(index, P_RETURN_LEVEL, 1)[0])
        except:
            return -1

    ## @brief Set the return level of a device.
    
    def setReturnLevel(self, index, value):
        return self.write(index, P_RETURN_LEVEL, [value])        

    ## @brief Turn on the torque of a servo.
    
    def enableTorque(self, index):
        return self.write(index, P_TORQUE_ENABLE, [1])

    ## @brief Turn on the torque of a servo.
    
    def disableTorque(self, index):
        return self.write(index, P_TORQUE_ENABLE, [0])

    ## @brief Set the status of the LED on a servo.
    
    def setLed(self, index, value):
        return self.write(index, P_LED, [value])

    ## @brief Set the position of a servo.
    
    def setPosition(self, index, value):
        return self.write(index, P_GOAL_POSITION_L, [value%256, value>>8])

    ## @brief Set the speed of a servo.
    
    def setSpeed(self, index, value):
        return self.write(index, P_GOAL_SPEED_L, [value%256, value>>8])

    ## @brief Get the position of a servo.
    
    def getPosition(self, index):
        values = self.read(index, P_PRESENT_POSITION_L, 2)
        try:
            return int(values[0]) + (int(values[1])<<8)
        except:
            return -1

    ## @brief Get the speed of a servo.
    
    def getSpeed(self, index):
        values = self.read(index, P_PRESENT_SPEED_L, 2)
        try:
            return int(values[0]) + (int(values[1])<<8)
        except:
            return -1
        
    ## @brief Get the goal speed of a servo.
    
    def getGoalSpeed(self, index):
        values = self.read(index, P_GOAL_SPEED_L, 2)
        try:
            return int(values[0]) + (int(values[1])<<8)
        except:
            return -1

    ## @brief Get the voltage of a device.
    
    def getVoltage(self, index):
        try:
            return int(self.read(index, P_PRESENT_VOLTAGE, 1)[0])/10.0
        except:
            return -1    

    ## @brief Get the temperature of a device.
    
    def getTemperature(self, index):
        try:
            return int(self.read(index, P_PRESENT_TEMPERATURE, 1)[0])
        except:
            return -1

    ## @brief Determine if a device is moving.
    
    def isMoving(self, index):
        try:
            d = self.read(index, P_MOVING, 1)[0]
        except:
            return True
        return d != 0
    
    ## @brief Put a servo into wheel mode (continuous rotation).
    
    def enableWheelMode(self, index):
        self.write(index, P_CCW_ANGLE_LIMIT_L, [0,0])

    ## @brief Put a servo into servo mode.
    
    def disableWheelMode(self, index, resolution=10):
        resolution = (2 ** resolution) - 1
        self.write(index, P_CCW_ANGLE_LIMIT_L, [resolution%256,resolution>>8])

    ## Direction definition for setWheelSpeed
    FORWARD = 0
    ## Direction definition for setWheelSpeed
    BACKWARD = 1

    ## @brief Set the speed and direction of a servo which is in wheel mode (continuous rotation).
    
    def setWheelSpeed(self, index, direction, speed):
        if speed > 1023:
            speed = 1023
        if direction == self.FORWARD:
            # 0~1023 is forward, it is stopped by setting to 0 while rotating to CCW direction.
            self.write(index, P_GOAL_SPEED_L, [speed%256, speed>>8])
        else:
            # 1024~2047 is backward, it is stopped by setting to 1024 while rotating to CW direction.
            speed += 1024
            self.write(index, P_GOAL_SPEED_L, [speed%256, speed>>8])

    ###########################################################################
    # Extended ArbotiX Driver

    ## Helper definition for analog and digital access.
    LOW = 0
    ## Helper definition for analog and digital access.
    HIGH = 0xff
    ## Helper definition for analog and digital access.
    INPUT = 0
    ## Helper definition for analog and digital access.
    OUTPUT = 0xff

    # ArbotiX-specific register table
    # We do Model, Version, ID, Baud, just like the AX-12
    ## Register base address for reading digital ports
    REG_DIGITAL_IN0 = 5
    REG_DIGITAL_IN1 = 6
    REG_DIGITAL_IN2 = 7
    REG_DIGITAL_IN3 = 8
    ## Register address for triggering rescan
    REG_RESCAN = 15
    # 16, 17 = RETURN, ALARM
    ## Register address of first analog port (read only).
    ## Each additional port is BASE + index.
    ANA_BASE = 18
    ## Register address of analog servos. Up to 10 servos, each
    ## uses 2 bytes (L, then H), pulse width (0, 1000-2000ms) (Write only)
    SERVO_BASE = 26
    # Address 46 is Moving, just like an AX-12
    REG_DIGITAL_OUT0 = 47

    ## @brief Force the ArbotiX2 to rescan the Dynamixel busses.
    def rescan(self):
        self.write(253, self.REG_RESCAN, [1,])

    ## @brief Get the value of an analog input pin.
    
    def getAnalog(self, index, leng=1):
        try:
            val = self.read(253, self.ANA_BASE+int(index), leng)
            return sum(val[i] << (i * 8) for i in range(leng))
        except:
            return -1

    ## @brief Get the value of an digital input pin.
    
    def getDigital(self, index):
        try:
            if index < 32:
                x = self.read(253, self.REG_DIGITAL_IN0 + int(index/8), 1)[0]
            else:
                return -1
        except:
            return -1
        if x & (2**(index%8)):
            return 255
        else:
            return 0

    ## @brief Get the value of an digital input pin.
    
    def setDigital(self, index, value, direction=0xff):
        if index > 31: return -1
        if value == 0 and direction > 0:
            self.write(253, self.REG_DIGITAL_OUT0 + int(index), [1])
        elif value > 0 and direction > 0:
            self.write(253, self.REG_DIGITAL_OUT0 + int(index), [3])
        elif value > 0 and direction == 0:
            self.write(253, self.REG_DIGITAL_OUT0 + int(index), [2])
        else:
            self.write(253, self.REG_DIGITAL_OUT0 + int(index), [0])
        return 0

    ## @brief Set the position of a hobby servo.
    
    def setServo(self, index, value):
        if index > 7: return -1
        if value != 0 and (value < 500 or value > 2500):
            print "ArbotiX Error: Servo value out of range:", value
        else:
            self.write(253, self._SERVO_BASE + 2*index, [value%256, value>>8])
        return 0