ssis-robotics / rvr

Control the Sphero RVR over the serial port, using Circuitpython

rvr

Control the Sphero RVR over the serial port, using Circuitpython

Documentation of protocol and code

The packages are well documented by @emwdx in his code for drive_to_position:

# Set up the serial port on the board
uart = busio.UART(board.TX, board.RX, baudrate=115200)

# This function takes in an angle, a pair of x and y coordinates, and a speed target to use for the RVR.
def drive_to_position_si(yaw_angle, x, y, speed):

  # This sets up the list of bytes needed for this command to be sent to the RVR through the serial port.
    SOP = 0x8d             # Always the start byte for a command to the RVR
    FLAGS = 0x06           # This tells the RVR to ignore the target and source ID, 
	                       # and that this command expects a response only if there are errors.
    TARGET_ID = 0x0e 
    SOURCE_ID = 0x0b
    DEVICE_ID = 0x16       # The drive system ID is 0x16
    COMMAND_ID = 0x38      # The drive_to_position_si command has ID of 38
    SEQ = 0x01             # The sequence value is arbitrarily 1. We aren't using the sequence capability here.
    EOP = 0xD8             # The final byte in the command is 0xD8

  # The command expects four float values for yaw angle, x coordinate, y coordinate, and speed. 
  # This lets you use decimal values.
  # The lines below convert the float values to a set of four bytes representing each value.
    yaw_angle = bytearray(struct.pack('>f', yaw_angle))
    x = bytearray(struct.pack('>f', x))
    y = bytearray(struct.pack('>f', y))
    speed = bytearray(struct.pack('>f', speed))
	
  # The command has a flags byte that lets you set different attributes for how the robot moves 
  # between the positions. Check out page 12 of the SpheroRVRControlSystem manual for the details.
    flags = bytearray(struct.pack('B', 0))

  # Now we build the command packet byte by byte. First the first five bytes:
    output_packet = [SOP, FLAGS, DEVICE_ID, COMMAND_ID, SEQ]

  # Now the bytes for the flags
    output_packet.extend(yaw_angle)
    output_packet.extend(x)
    output_packet.extend(y)
    output_packet.extend(speed)
    output_packet.extend(flags)
  # And the checksum byte which does some math with the sum of the previous 
  # bytes in the command, and finally the end of packet byte.
    output_packet.extend([~((sum(output_packet) - SOP) % 256) & 0x00FF,EOP])

  # Now that the command is complete, return the command as an array of bytes.
    return bytearray(output_packet)

# END OF DRIVE_TO_POSITION_SI