Rover: use scheduler ticks in place of mainloop_count

APMrover2/APMrover2.cpp

@@ -138,9 +138,6 @@ void Rover::loop()
     G_Dt                = (timer - fast_loopTimer_us) * 1.0e-6f;
     fast_loopTimer_us   = timer;
 
-    // for mainloop failure monitoring
-    mainLoop_count++;
-
     // tell the scheduler one tick has passed
     scheduler.tick();
 

APMrover2/Rover.h

@@ -337,8 +337,6 @@ private:
     // System Timers
     // Time in microseconds of start of main control loop.
     uint32_t fast_loopTimer_us;
-    // Counter of main loop executions.  Used for performance monitoring and failsafe processing
-    uint16_t mainLoop_count;
 
     // set if we are driving backwards
     bool in_reverse;

APMrover2/failsafe.cpp

@@ -16,13 +16,14 @@
  */
 void Rover::failsafe_check()
 {
-    static uint16_t last_mainLoop_count;
+    static uint16_t last_ticks;
     static uint32_t last_timestamp;
     const uint32_t tnow = AP_HAL::micros();
 
-    if (mainLoop_count != last_mainLoop_count) {
+    const uint16_t ticks = scheduler.ticks();
+    if (ticks != last_ticks) {
         // the main loop is running, all is OK
-        last_mainLoop_count = mainLoop_count;
+        last_ticks = ticks;
         last_timestamp = tnow;
         return;
     }