Passing parameters to state machine in PIO

[Prakhar005]

Hello all,

I am working on defining a state machine using the PIO functionality of raspberry Pico. I am using micropython for defining the program. In my state machine, I would like to set the scratch registers 'x' and 'y' by passing user-defined parameters to the state machine program. However, it seems there is no direct way to pass arguments to the state machine program. I was wondering if anyone has any hints on how to solve this issue? thank you!

[Vendelator]

If I understand what you want to do, you need to first put data into PIO and then PULL from inside an SM.

import rp2

@rp2.asm_pio()
def pio_function():
    pull()
    mov(x, osr)

sm_0 = rp2.StateMachine(0, pio_function, freq=10_000)
user_parameter = int(input("Write user input: "))
sm_0.put(user_parameter)

Something along those lines.

BR

[Prakhar005]

Thank you for the suggested implementation. This makes a lot of sense! I use 'x' register as a counter which decrements to zero in the state machine. However, when the state machine wraps back to the start, I would like 'x' to be initialized again with the same user-specified value. I am unable to figure out how to re-initialize it. Is there a way to implement the 'put' command in the state machine itself and pass 'user_parameter' as an argument to 'pro_function()'. Thank you for the help! :)

[Vendelator]

I am guessing now. Because I am very much a beginner with this.

But if you:

mov(y, osr)
mov(x, y)

y should not get "used up" and keep refilling x.

I saw in another example they did like this to keep refilling the program. I assume X will then change when a new value is put into it. (copied from OSR)

@rp2.asm_pio(set_init=rp2.PIO.OUT_LOW)
def stepper():
    pull(noblock)
    mov(x, osr
    mov(y, x)

    jmp(not_x, "end")

    label("delay")
    jmp(x_dec, "delay")

    label("end")
    mov(x, y)

[Prakhar005]

Thank you for the help! I tried to implement your idea and it works very well. Thank you!

[Vendelator]

This I great news, I have learned from this as well.

Good luck with your coding.