Parallel while loops in python for motor control and data acquisition

Question

Let's say I've got two functions:

def moveMotorToPosition(position,velocity) 
    #moves motor to a particular position
    #does not terminate until motor is at that position

and

def getMotorPosition() 
    #retrieves the motor position at any point in time

In practice what I want to be able to have the motor oscillating back and forth (by having a loop that calls moveMotorToPosition twice; once with a positive position and one with a negative position)

While that 'control' loop is iterating, I want a separate while loop to be pulling data at some frequency by calling getMotorPositionnd. I would then set a timer on this loop that would let me set the sampling frequency.

In LabView (the motor controller supplies a DLL to hook into) I achieve this with 'parallel' while loops. I've never done anything with parallel and python before, and not exactly sure which is the most compelling direction to head.

Answer 1

To point you a little closer to what it sounds like you're wanting:

import threading

def poll_position(fobj, seconds=0.5):
    """Call once to repeatedly get statistics every N seconds."""
    position = getMotorPosition()

    # Do something with the position.
    # Could store it in a (global) variable or log it to file.
    print position
    fobj.write(position + '\n')

    # Set a timer to run this function again.
    t = threading.Timer(seconds, poll_position, args=[fobj, seconds])
    t.daemon = True
    t.start()

def control_loop(positions, velocity):
    """Repeatedly moves the motor through a list of positions at a given velocity."""
    while True:
        for position in positions:
            moveMotorToPosition(position, velocity)

if __name__ == '__main__':
    # Start the position gathering thread.
    poll_position()
    # Define `position` and `velocity` as it relates to `moveMotorToPosition()`.
    control_loop([first_position, second_position], velocity)