Fix alarm.wake_alarm not set after deep sleep on pi pico

[georgboe]

Hi,

EDIT: Fixes #6483.

I would like to see this issue fixed, so I had a look at it.

The problem here seems to be that watchdog's scratch register is read and alarm.wake_alarm is assigned in run_boot_py as a part of start_mp. Afterwards the scratch register is cleared by alarm_reset (https://github.com/adafruit/circuitpython/blob/main/ports/raspberrypi/common-hal/alarm/__init__.c#L105). By the time we get to run_code_py the scratch register has already been cleared and we have nothing that indicates that we have woken from deep sleep so alarm.wake_alarm is set to None.

I'm not sure how you'd like this to be fixed. But if you can please have a look at the changes and suggest improvements or a different approach, I'd willing to change it.

[dhalbert]

Thanks for the insight! This is not a problem on ESP32-nn alarms because the "alarm happened" state is not cleared by alarm_reset(), but it is on RP2040, as you diagnosed. I am taking a look to see what the best way to fix this would be. There might be some issues not doing alarm_reset() during run_boot_py() if some pins are going to be used.

[dhalbert]

Note to myself: fix should also take #6476 into account. That is on Espressif, but there may be a more general solution here.

[dhalbert]

Subsumed by #7154.