Allow USB recovery boot without charging an unsafe battery

[TobiasRoeddiger]

A battery rejected by the normal power manager can leave the application waiting before USB starts, making USB diagnosis and reflashing unavailable. Add an automatic USB-only recovery boot to the 2.3.0 FOTA configuration (release branch 2.2.10).

• Assert the charger CD pin before checked, bounded gauge reads. Keep it high for the whole recovery session if the gauge is unavailable/uninitialized or reports an unsafe battery condition.
• Start USB mcumgr without normal battery workers, Bluetooth, audio or sensors. Skip the normal DFU indicator callback because those services are not initialized.
• Power off on USB removal and wake on USB insertion. Healthy USB boots, safe precharging and battery-only boots retain their normal behavior; non-FOTA builds do not enable this feature.
• Preserve the charger's read-to-clear reset indication by not reading that register during the probe.

Validation: full NCS 3.4.1 FOTA and non-FOTA builds passed. All 12 control-logic tests passed on the host with AddressSanitizer/UndefinedBehaviorSanitizer, including gauge/GPIO failures, threshold boundaries, USB removal and latched inhibition. The tests are also registered in the existing Unity/Twister suite.

Draft pending hardware validation: USB image listing/upload, unplug/replug, CD and battery-current measurements, and operation across the PMIC watchdog interval. No device was flashed. Charge inhibition begins in the application, not before MCUboot; the battery is not physically isolated. This cannot retroactively recover an old firmware that never starts USB. Details and the read-only mcumgr image list command are in docs/usb-battery-recovery.md.

[github-actions]

✅ Unit tests passed

6 passed, 0 failed/error, 0 skipped — view workflow run

Test scenario	Platform	Result
openearable.unit.sensor_component	native_sim/native/64	✅ passed
openearable.unit.sensor_transport	native_sim/native/64	✅ passed
openearable.unit.usb_recovery	native_sim/native/64	✅ passed
openearable.unit.ring_buffer	native_sim/native/64	✅ passed
openearable.unit.audio_encoder	native_sim/native/64	✅ passed
openearable.unit.audio_startup	native_sim/native/64	✅ passed

Download the unit-test-results artifact for full Twister reports and logs.

[github-actions]

Compiler warnings

The extended-warning build completed successfully.

Application compiler warnings

Show warnings

unicast_server/main.cpp:91:33: warning: 'int usb_enable(usb_dc_status_callback)' is deprecated [-Wdeprecated-declarations]
src/Battery/usb_recovery_io.c:99:9: warning: 'usb_disable' is deprecated [-Wdeprecated-declarations]
src/Battery/usb_recovery_io.c:121:9: warning: 'usb_enable' is deprecated [-Wdeprecated-declarations]

View this workflow run

[github-actions]

Build output available:
openearable_v2_firmware.zip
openearable_v2_fota.zip

[github-actions]

CodeChecker static analysis

✅ No non-style issues found.