AP_BoardConfig: allow for heater polarity setting on FMU

libraries/AP_BoardConfig/IMU_heater.cpp

@@ -27,6 +27,10 @@
 
 extern const AP_HAL::HAL& hal;
 
+#ifndef HAL_HEATER_GPIO_ON
+#define HAL_HEATER_GPIO_ON 1
+#endif
+
 void AP_BoardConfig::set_imu_temp(float current)
 {
     int8_t target = heater.imu_target_temperature.get();
@@ -37,7 +41,7 @@ void AP_BoardConfig::set_imu_temp(float current)
     if (target == -1) {
         // nothing to do, make sure heater is left off
 #if defined(HAL_HEATER_GPIO_PIN)
-        hal.gpio->write(HAL_HEATER_GPIO_PIN, false);
+        hal.gpio->write(HAL_HEATER_GPIO_PIN, !HAL_HEATER_GPIO_ON);
 #endif
         return;
     }
@@ -57,7 +61,7 @@ void AP_BoardConfig::set_imu_temp(float current)
         // output as duty cycle to local pin. Use a random sequence to
         // prevent a periodic change to magnetic field
         bool heater_on = (get_random16() < uint32_t(heater.output) * 0xFFFFU / 100U);
-        hal.gpio->write(HAL_HEATER_GPIO_PIN, heater_on);
+        hal.gpio->write(HAL_HEATER_GPIO_PIN, heater_on?HAL_HEATER_GPIO_ON : !HAL_HEATER_GPIO_ON);
 #endif
         return;
     }