Stop accelerometer thread when double-tap/wake-on-motion disabled at runtime (#11025)

* Stop accelerometer thread when double-tap/wake-on-motion disabled at runtime

double_tap_as_button_press and wake_on_tap_or_motion are applied live: the
OFF->ON edge calls accelerometerThread->start(), but there was no ON->OFF
branch, so turning either flag off left the sensor thread running (polling
I2C, drawing power) until reboot. Worse, because enabled stayed true, a later
OFF->ON edge was a no-op (the enabled==false guard blocked re-start), leaving
the feature un-restartable without a reboot.

Add the symmetric ON->OFF branch in both handlers. When a flag goes true->off
and the other consumer of the shared thread is also off, call
accelerometerThread->disable() (stops runOnce polling and clears enabled so a
later re-enable can start() again). Each branch checks the other flag first so
disabling one feature never stops the sensor while the other still needs it.

* Keep accelerometer thread running when its sensor drives the compass

* Guard accelerometer thread config toggles against a null thread pointer

* AdminModule: factor shared accelerometer start/stop into a helper

The device and display config handlers had mirror-image blocks reconciling the
shared accelerometer thread. Extract reconcileAccelerometerThread(wasOn, nowOn,
otherFeatureOn) so the null guard, edge logic, compass (providesHeading) guard,
and rationale live in one place; each call site is now a single call. Behavior
is unchanged. Also drops the redundant per-field assignment that the
whole-struct `config.device = ...` / `config.display = ...` overwrites anyway.

---------

Co-authored-by: Thomas Göttgens <tgoettgens@gmail.com>

src/modules/AdminModule.cpp

@@ -786,6 +786,27 @@ void AdminModule::handleSetOwner(const meshtastic_User &o)
     }
 }
 
+#if !defined(ARCH_PORTDUINO) && !defined(ARCH_STM32WL) && !MESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR &&                            \
+    !MESHTASTIC_EXCLUDE_ACCELEROMETER
+// Shared by double-tap-as-button (device) and wake-on-motion (display). Start on either flag's
+// off->on edge; stop on the on->off edge once neither needs it (disable() clears `enabled` so a
+// later re-enable restarts). Skip the stop if the sensor also drives the compass, else the heading
+// freezes until reboot. wasOn/nowOn = old/new of the changed flag; otherFeatureOn = the other flag.
+static void reconcileAccelerometerThread(bool wasOn, bool nowOn, bool otherFeatureOn)
+{
+    if (!accelerometerThread) // null unless a sensor was detected at boot
+        return;
+
+    if (!wasOn && nowOn && accelerometerThread->enabled == false) {
+        accelerometerThread->enabled = true;
+        accelerometerThread->start();
+    } else if (wasOn && !nowOn && !otherFeatureOn && accelerometerThread->enabled == true &&
+               !accelerometerThread->providesHeading()) {
+        accelerometerThread->disable();
+    }
+}
+#endif
+
 void AdminModule::handleSetConfig(const meshtastic_Config &c, bool fromOthers)
 {
     auto changes = SEGMENT_CONFIG;
@@ -801,12 +822,8 @@ void AdminModule::handleSetConfig(const meshtastic_Config &c, bool fromOthers)
         config.has_device = true;
 #if !defined(ARCH_PORTDUINO) && !defined(ARCH_STM32WL) && !MESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR &&                            \
     !MESHTASTIC_EXCLUDE_ACCELEROMETER
-        if (config.device.double_tap_as_button_press == false && c.payload_variant.device.double_tap_as_button_press == true &&
+        reconcileAccelerometerThread(config.device.double_tap_as_button_press,
-            accelerometerThread->enabled == false) {
+                                     c.payload_variant.device.double_tap_as_button_press, config.display.wake_on_tap_or_motion);
-            config.device.double_tap_as_button_press = c.payload_variant.device.double_tap_as_button_press;
-            accelerometerThread->enabled = true;
-            accelerometerThread->start();
-        }
 #endif
         if (config.device.button_gpio == c.payload_variant.device.button_gpio &&
             config.device.buzzer_gpio == c.payload_variant.device.buzzer_gpio &&
@@ -905,12 +922,8 @@ void AdminModule::handleSetConfig(const meshtastic_Config &c, bool fromOthers)
         }
 #if !defined(ARCH_PORTDUINO) && !defined(ARCH_STM32WL) && !MESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR &&                            \
     !MESHTASTIC_EXCLUDE_ACCELEROMETER
-        if (config.display.wake_on_tap_or_motion == false && c.payload_variant.display.wake_on_tap_or_motion == true &&
+        reconcileAccelerometerThread(config.display.wake_on_tap_or_motion, c.payload_variant.display.wake_on_tap_or_motion,
-            accelerometerThread->enabled == false) {
+                                     config.device.double_tap_as_button_press);
-            config.display.wake_on_tap_or_motion = c.payload_variant.display.wake_on_tap_or_motion;
-            accelerometerThread->enabled = true;
-            accelerometerThread->start();
-        }
 #endif
         config.display = c.payload_variant.display;
         break;

src/motion/AccelerometerThread.h

@@ -60,6 +60,10 @@ class AccelerometerThread : public concurrency::OSThread
         }
     }
 
+    // True if the active sensor drives the compass heading in runOnce(). Callers must not
+    // disable() the thread in this case, or the compass would freeze until the next reboot.
+    bool providesHeading() const { return isInitialised && sensor && sensor->providesHeading(); }
+
   protected:
     int32_t runOnce() override
     {

src/motion/BMM150Sensor.h

@@ -50,6 +50,7 @@ class BMM150Sensor : public MotionSensor
 
     // Called each time our sensor gets a chance to run
     virtual int32_t runOnce() override;
+    virtual bool providesHeading() const override { return true; }
 };
 
 #endif

src/motion/BMX160Sensor.h

@@ -25,6 +25,7 @@ class BMX160Sensor : public MotionSensor
     virtual bool init() override;
     virtual int32_t runOnce() override;
     virtual void calibrate(uint16_t forSeconds) override;
+    virtual bool providesHeading() const override { return true; }
 };
 
 #else

src/motion/ICM20948Sensor.h

@@ -100,6 +100,7 @@ class ICM20948Sensor : public MotionSensor
     // Called each time our sensor gets a chance to run
     virtual int32_t runOnce() override;
     virtual void calibrate(uint16_t forSeconds) override;
+    virtual bool providesHeading() const override { return true; }
 };
 
 #endif

src/motion/MotionSensor.h

@@ -42,6 +42,12 @@ class MotionSensor
 
     virtual void calibrate(uint16_t forSeconds){};
 
+    // True if this sensor produces the compass heading (screen->setHeading()) in runOnce().
+    // Combined accel+magnetometer parts (e.g. BMX160, ICM20948) and standalone magnetometers
+    // handled by the accelerometer thread (e.g. BMM150) override this. Used to avoid halting
+    // the thread - and freezing the compass - when motion-only features are disabled at runtime.
+    inline virtual bool providesHeading() const { return false; };
+
   protected:
     // Turn on the screen when a tap or motion is detected
     virtual void wakeScreen();