pico - zombie pio state machines after soft reset

version:

>>> import sys
>>> sys.implementation
(name='micropython', version=(1, 19, 1), _machine='Raspberry Pi Pico with RP2040', _mpy=4102)

Problem description: pio sm instances can be unexpectedly resucitated after a soft reset

More detailed description:

• instantiate and activate many pio state machines with the same pio program
• call machine.soft_reset()
• instantiate and activate only one sm, with the same pio program
• Expected: only one sm activelly driven his output
• Observed: all sm with same pio program will be activelly driven their outputs

The demo script expects to have led + resistor in gpios 10..13

It will instantiate and activate four sm, each blinling a led, do a soft reset, instantiate and activate only one sm, do a hard reset and repeat.

Expected 5 seconds of four led blinking, followed by 5 seconds of only one led blinking, repeat

Observed always four leds blinking

See docstring for instuctions to run

demo script: pio_and_machine_reset.py

""" demoing zombie state machines after soft reset

Using a pico lean and mean, not W or other variants
HW: led + resistor on gpios 10..13

Shoul do: blink the four leds 5 seconds, then blink only the led in gpio 13
Observed: four leds blinking always

Operation:
   - if not first run, ensure the file 'soft_reset_flag.txt' does not
     exist in the pico
   - Close Thonny or other runner / debugger to discard other sw interference 
   - Unplug and plug the pico to ensure a hard reset
   - Use minicom or Bootterm ( bt ) to get the serial output from the pico
"""

from machine import Pin
from rp2 import PIO, StateMachine, asm_pio
import time

def report_state_machines():
    for p in (0, 1):
        for sm_c in range(4):
            fmt = "rp2.PIO(%d).state_machine(%d).active(): %s"
            print( fmt % (p, sm_c, rp2.PIO(p).state_machine(sm_c).active()))

class FSFlag:
    def __init__(self, name):
        self.name = name
        self.fname = name + "_flag.txt"
        
    def is_flag_set(self):
        present = False
        try:
            f = open(self.fname, "r")
            present = True
            f.close()
        except Exception:
            present = False
        return present

    def set_(self):
        f = open(self.fname, "w")
        f.write("flag file")
        f.close()

    def clear(self):
        import os
        if self.is_flag_set():
            os.remove(self.fname)

    def value(self, val=None):
        if val is None:
            return self.is_flag_set()
        elif val:
            self.set_()
        else:
            self.clear()


@rp2.asm_pio(set_init=rp2.PIO.OUT_LOW)
def blink():
    set(pins, 1)   [31]
    nop()          [31]
    nop()          [31]
    nop()          [31]
    nop()          [31]
    set(pins, 0)   [31]
    nop()          [31]
    nop()          [31]
    nop()          [31]
    nop()          [31]

def blink_1_led(dt):
    print("only led on gpio 13 should blink")
    print("only SM 3 should be active")
    sm = StateMachine(3, blink, freq=2000, set_base=Pin(13, Pin.OUT, value=0))
    sm.active(1)
    report_state_machines()
    time.sleep(dt)

def blink_4_leds(dt):
    print("leds in gpios (10, 11, 12, 13) should blink")
    print("SMs 0..4 should be active")
    gpios = (10, 11, 12, 13)
    py_sm_ids = (0, 1, 2, 3)
    pairs = [(id_, Pin(gp, Pin.OUT, value=0)) for id_, gp in zip(py_sm_ids, gpios)]
    sms = {id_: StateMachine(id_, blink, freq=2000, set_base=pin) for id_, pin in pairs} 
    for sm in sms.values():
        sm.active(1)
    report_state_machines()
    time.sleep(dt)

print("Comming Alive")
report_state_machines()
soft_reset = FSFlag("soft_reset")
if soft_reset.value():
    print("after soft reset")
    blink_1_led(5)
    soft_reset.value(0)
    machine.reset()
else:
    print("after hard reset")
    blink_4_leds(5)
    soft_reset.value(1)
    machine.soft_reset()

Additional info, not demoed but can easily show with variants on the demo code:

• always after soft reset all the sm active before the reset are shown as active by rp2.PIO(p).state_machine(sm_c).active()
• if no sm is instantiated after the soft reset, no pin activity shows in the pins controlled by the old sm's
• if a pio sm with a different pio program is instantiated after the soft reset, no pin activity shows in the pins controlled by the old sm's
• if a pio sm with same pio program is activated after the soft reset, the old sm's activelly drive their pins

This issue is probably related to
https://forums.raspberrypi.com/viewtopic.php?t=340099
https://github.com/thonny/thonny/issues/2455

Start with the repro in pio_and_machine_reset.py and run it on a Raspberry Pi Pico with LEDs on GPIOs 10–13. Inspect the machine.soft_reset and rp2.PIO state_machine active behavior described in the report. Done means that after soft reset, only the newly activated state machine drives its output and the previous machines are inactive.