Baro: health check that values are changing

libraries/AP_Baro/AP_Baro.cpp

@@ -517,10 +517,10 @@ void AP_Baro::update(void)
     }
 
     // consider a sensor as healthy if it has had an update in the
-    // last 0.5 seconds
+    // last 0.5 seconds and values are non-zero and have changed within the last 2 seconds
     uint32_t now = AP_HAL::millis();
     for (uint8_t i=0; i<_num_sensors; i++) {
-        sensors[i].healthy = (now - sensors[i].last_update_ms < 500) && !is_zero(sensors[i].pressure);
+        sensors[i].healthy = (now - sensors[i].last_update_ms < BARO_TIMEOUT_MS) && (now - sensors[i].last_change_ms < BARO_DATA_CHANGE_TIMEOUT_MS) && !is_zero(sensors[i].pressure);
     }
 
     for (uint8_t i=0; i<_num_sensors; i++) {

libraries/AP_Baro/AP_Baro.h

@@ -12,6 +12,10 @@
 // multiple sensor instances
 #define BARO_MAX_DRIVERS 3
 
+// timeouts for health reporting
+#define BARO_TIMEOUT_MS                 500     // timeout in ms since last successful read
+#define BARO_DATA_CHANGE_TIMEOUT_MS     2000    // timeout in ms since last successful read that involved temperature of pressure changing
+
 class AP_Baro_Backend;
 
 class AP_Baro
@@ -169,6 +173,7 @@ private:
     struct sensor {
         baro_type_t type;                   // 0 for air pressure (default), 1 for water pressure
         uint32_t last_update_ms;        // last update time in ms
+        uint32_t last_change_ms;        // last update time in ms that included a change in reading from previous readings
         bool healthy:1;                 // true if sensor is healthy
         bool alt_ok:1;                  // true if calculated altitude is ok
         bool calibrated:1;              // true if calculated calibrated successfully

libraries/AP_Baro/AP_Baro_Backend.cpp

@@ -17,7 +17,15 @@ void AP_Baro_Backend::_copy_to_frontend(uint8_t instance, float pressure, float
     if (instance >= _frontend._num_sensors) {
         return;
     }
+    uint32_t now = AP_HAL::millis();
+
+    // check for changes in data values
+    if (!is_equal(_frontend.sensors[instance].pressure, pressure) || !is_equal(_frontend.sensors[instance].temperature, temperature)) {
+        _frontend.sensors[instance].last_change_ms = now;
+    }
+
+    // update readings
     _frontend.sensors[instance].pressure = pressure;
     _frontend.sensors[instance].temperature = temperature;
-    _frontend.sensors[instance].last_update_ms = AP_HAL::millis();
+    _frontend.sensors[instance].last_update_ms = now;
 }