using PIO on Pico for STEP/DIR interface

[Chr157i4n]

Describe the feature
The Raspberry Pi Pico has PIO channels that can be used to offload at least the switching of the STEP pin.

I think the best way to implement this cleanly is with an additional MotionControl module (e.g. TmcMotionControlStepPIODir), which then uses a PIO for the STEP pin.

This is not necessary for EN and DIR.

Ideally, this should be implemented for both MicroPython and CircuitPython within this module. Unfortunately, the interfaces for accessing the PIOs differ:
https://docs.micropython.org/en/latest/rp2/tutorial/pio.html
https://docs.circuitpython.org/en/latest/shared-bindings/rp2pio

[Chr157i4n]

Unfortunately, CircuitPython and MicroPython use different methods to write the code for the PIO. Ideally, the code should not be duplicated.

MicroPython

uses @rp2.asm_pio and PIO-ASM inline in the Python code

import rp2

@rp2.asm_pio(set_init=rp2.PIO.OUT_LOW)
def step_program():
    # Assembly code here
    # ...

CircuitPython

uses adafruit_pioasm or precompiled PIO binaries

from adafruit_pioasm import Program
from rp2pio import StateMachine

_asm_str = """
Assembly code here
...
"""

program = Program(_asm_str)
sm = StateMachine(program.assembled, ...)

Furthermore, CircuitPython does not support interrupts.

Currently, interrupts from the PIO are used to inform the controller of the number of steps the PIO already made. This does not work with CircuitPython. One possible solution would be to send a block via the TX-FIFO to signal that the movement is complete.