RAK3401: reliable AIN1 button — interrupt latch, debounce, digital read, instant screen-on 🤖🤖

[disq]

Problem

The RAK3401 companion build has a single user button on AIN1 (P0.31), driven by analogRead() polled once per main-loop iteration — there is no interrupt serving it. Symptoms:

• Presses dropped when the loop briefly stalls (LoRa RX/TX, BLE, flash writes).
• Single clicks feel laggy: the screen only wakes after the multi-click window expires.
• The button can't wake the device from hibernate (SYSTEMOFF) — and a naive GPIO SENSE wake makes it wake instantly and never stay off.

This PR makes the AIN1 button story self-contained: reliable input and a working hibernate wake. It folds in #2642's RAK3401 board pieces (so that PR can be closed in favor of this one).

Changes

MomentaryButton (generic)

• Configurable multi-click window on the analog constructor (default unchanged).
• reset() — abandon the in-flight gesture.
• enableInterrupt() — permanent FALLING-edge GPIOTE interrupt that latches presses so they survive loop stalls. Debounced: one count per press, re-armed only after check() sees a clean release (rejects press/release contact bounce). Skipped for analog/SAADC-threshold buttons (GPIOTE vs analogRead conflict on the same pin).

companion_radio UITask

• Wake the display instantly on the press edge when it's off, instead of after the multi-click window.
• Arm the button interrupt at startup for PIN_USER_BTN_ANA boards.

variants/rak3401 — input

• Read AIN1 digitally (active-low, internal pull-up) instead of via SAADC — digitalRead coexists with the GPIOTE edge interrupt where analogRead does not (analogRead otherwise reads stuck "always pressed" once the interrupt is attached). Multi-click retained: single=NEXT / double=PREV / triple=SELECT / long=ENTER.

Hibernate wake via LPCOMP (2nd commit; supersedes #2642's GPIO-SENSE approach)

• NRF52Board::configureVoltageWake() gains a detect_down param (default false = UP crossing for voltage recovery; true = DOWN crossing for a button press), selecting ANADETECT Down/Up and INTENSET DOWN/UP accordingly.
• RAK3401Board.h: powerOff() override routing through initiateShutdown(USER).
• RAK3401Board::initiateShutdown(): when PIN_USER_BTN_ANA is defined, arm LPCOMP on AIN7 at REFSEL 3 (~½ VDD) for a DOWN crossing as the SYSTEMOFF wake source. Waits for a confirmed release (analogRead above threshold) before arming, bounded by a 5 s timeout. Channel/threshold overridable via PWRMGT_BTN_LPCOMP_AIN / PWRMGT_BTN_LPCOMP_REFSEL.

Why LPCOMP, not GPIO SENSE

AIN1 is wired as an analog button (pressed == analogRead() < threshold). Its digital input buffer reads the released idle level as LOW even though analogRead reports ~VDD, so arming SENSE_Low latches DETECT the instant we enter SYSTEMOFF — sd_power_system_off() returns immediately and the fall-through reset reboots ("instant wake"). LATCH/EVENTS_PORT clearing and release debounce don't help, because the released level itself reads LOW digitally. LPCOMP operates in the analog domain and sees the idle level correctly, so a DOWN-crossing arm works: released idles above threshold, a press pulls below → wake.

Relationship to #2642

This supersedes #2642 — it ports #2642's powerOff() override and AIN SYSTEMOFF wake, but replaces the GPIO-SENSE wake (which instant-wakes on this pin) with the LPCOMP approach. #2642 can be closed once this lands.

Testing

• Builds clean: RAK_3401_companion_radio_ble, RAK_3401_companion_radio_usb.
• Button input bench-tested on RAK3401 companion_radio_ble hardware: digital read fixes the SAADC+GPIOTE "always pressed" conflict; presses reliable through loop stalls; single/double/triple/long all work, no dropped or double-counted clicks.
• Hibernate: GPIO-SENSE instant-wakes on this pin (confirmed on hardware); the LPCOMP DOWN-crossing approach is the fix. Please re-flash/re-test the hibernate path before merge.

Known edge case

If the loop stalls through the middle of a fast double-click so check() never re-arms between the two presses, the second press is dropped (fails toward "one click", never a phantom extra). Normal clicking is unaffected.

🤖 Generated with Claude Code

[disq]

Probably not needed.