mightResetPid docs (#912)

firmware/controllers/actuators/idle_thread.cpp

@@ -51,7 +51,10 @@ EXTERN_ENGINE
 ;
 
 static bool shouldResetPid = false;
-// we might reset PID state when the state is changed, but only if needed (See autoIdle())
+// The idea of 'mightResetPid' is to reset PID only once - each time when TPS > idlePidDeactivationTpsThreshold.
+// The throttle pedal can be pressed for a long time, making the PID data obsolete (thus the reset is required).
+// We set 'mightResetPid' to true only if PID was actually used (i.e. idlePid.getOutput() was called) to save some CPU resources.
+// See automaticIdleController().
 static bool mightResetPid = false;
 
 #if EFI_IDLE_INCREMENTAL_PID_CIC