AP_Compass_AK8963: support for timesliced timers

fallback in case the current scheduler doesn't support it

libraries/AP_Compass/AP_Compass_AK8963.cpp

@@ -160,7 +160,8 @@ bool AP_Compass_AK8963::init()
     /* register the compass instance in the frontend */
     _compass_instance = register_compass();
     set_dev_id(_compass_instance, _bus->get_dev_id());
-    hal.scheduler->register_timer_process(FUNCTOR_BIND_MEMBER(&AP_Compass_AK8963::_update, void));
+    /* timer needs to be called every 10ms so set the freq_div to 10 */
+    _timesliced = hal.scheduler->register_timer_process(FUNCTOR_BIND_MEMBER(&AP_Compass_AK8963::_update, void), 10);
 
     _bus_sem->give();
     hal.scheduler->resume_timer_procs();
@@ -230,8 +231,8 @@ void AP_Compass_AK8963::_update()
     Vector3f raw_field;
     uint32_t time_us = AP_HAL::micros();
 
-
-    if (AP_HAL::micros() - _last_update_timestamp < 10000) {
+    if (!_timesliced &&
+        AP_HAL::micros() - _last_update_timestamp < 10000) {
         goto end;
     }
 

libraries/AP_Compass/AP_Compass_AK8963.h

@@ -83,6 +83,7 @@ private:
     bool                _initialized;
     uint32_t            _last_update_timestamp;
     uint32_t            _last_accum_time;
+    bool                _timesliced;
 
     AP_AK8963_SerialBus *_bus = nullptr;
     AP_HAL::Semaphore *_bus_sem;