Sub: use scheduler ticks in place of mainloop_count

ArduSub/ArduSub.cpp

@@ -129,9 +129,6 @@ void Sub::loop()
     G_Dt                    = (float)(timer - fast_loopTimer) / 1000000.0f;
     fast_loopTimer          = timer;
 
-    // for mainloop failure monitoring
-    mainLoop_count++;
-
     // Execute the fast loop
     // ---------------------
     fast_loop();

ArduSub/Sub.cpp

@@ -53,7 +53,6 @@ Sub::Sub(void)
           circle_nav(inertial_nav, ahrs_view, pos_control),
           pmTest1(0),
           fast_loopTimer(0),
-          mainLoop_count(0),
           in_mavlink_delay(false),
           param_loader(var_info),
           last_pilot_yaw_input_ms(0)

ArduSub/Sub.h

@@ -405,8 +405,6 @@ private:
     // --------------
     // Time in microseconds of main control loop
     uint32_t fast_loopTimer;
-    // Counter of main loop executions.  Used for performance monitoring and failsafe processing
-    uint16_t mainLoop_count;
 
     // Reference to the relay object
     AP_Relay relay;

ArduSub/failsafe.cpp

@@ -6,7 +6,7 @@
  */
 
 static bool failsafe_enabled = false;
-static uint16_t failsafe_last_mainLoop_count;
+static uint16_t failsafe_last_ticks;
 static uint32_t failsafe_last_timestamp;
 static bool in_failsafe;
 
@@ -30,9 +30,10 @@ void Sub::mainloop_failsafe_check()
 {
     uint32_t tnow = AP_HAL::micros();
 
-    if (mainLoop_count != failsafe_last_mainLoop_count) {
+    const uint16_t ticks = scheduler.ticks();
+    if (ticks != failsafe_last_ticks) {
         // the main loop is running, all is OK
-        failsafe_last_mainLoop_count = mainLoop_count;
+        failsafe_last_ticks = ticks;
         failsafe_last_timestamp = tnow;
         if (in_failsafe) {
             in_failsafe = false;