RP2040: Deep sleep until alarm without reset

[rgov]

Since the RP2040 preserves RAM when in the dormant (deep sleep) state, is it not possible to resume the program after an alarm, without resetting the board? This would make it significantly easier to preserve state while dropping into lower power modes.

@ghubcoder's blog post describes how to recover from the dormant state after an RTC alarm. This was implemented for MicroPython in modpicosleep.c (accompanying blog post).

[dhalbert]

I think we could do this for "light sleep", and make light sleep be a deeper sleep.

[bablokb]

@rgov: you could test the artifact of PR #10023. This will use dormant mode without reset for lightsleep like you suggested. According to my measurements, we are now in the same range as the blog-post claims for MicroPython.