Screen wake and sleep.

The screen wakes on any configured source (dial, button, motion, light) and sleeps after the idle timeout with no activity. Publishes :power events (:awake / :asleep).

To keep the screen on (an alarm, a settings screen), take a hold:

{:ok, hold} = NestGen2.Power.keep_awake(:alarm)
# ... the screen is on and won't sleep from idleness ...
:ok = NestGen2.Power.release(hold)

Holds stack: idle sleep resumes once every hold is released, starting a fresh idle timeout then. A hold is released automatically if the process that took it exits, so a crash can't leave the screen on for good. sleep/0 still turns the screen off when asked, holds or not.

Deep sleep

With deep_sleep on (config, or set_deep_sleep/1), once the screen has been asleep for deep_sleep_after_ms (10 s) with no holds, the whole system suspends to RAM, as Nest's own software does: the processor, radios and every process stop, and carry on exactly where they were when it wakes. That's what lets the battery charge on the base, which supplies only about 120 mA; awake all the time, the Nest drains its battery even on the base.

It wakes on the button, on the base (which wakes it for motion), or after deep_sleep_max_s (270 s) to keep in touch with the base. A wake-up that doesn't wake the screen goes back to sleep after deep_sleep_awake_ms (8 s). While suspended nothing runs: timers pause (they count awake time only), Wi-Fi drops and reconnects within a few seconds of waking. Apps that show changing data should refresh it on {:nest_gen2, :power, :awake}.