part of 2217 which may fix it alone (#2220)

firmware/controllers/algo/event_registry.h

@@ -58,6 +58,9 @@ class FuelSchedule {
 public:
 	FuelSchedule();
 
+	// Call this function if something happens that requires a rebuild, like a change to the trigger pattern
+	void invalidate();
+
 	// Call this every trigger tooth.  It will schedule all required injector events.
 	void onTriggerTooth(size_t toothIndex, int rpm, efitick_t nowNt DECLARE_ENGINE_PARAMETER_SUFFIX);
 
@@ -73,10 +76,7 @@ public:
 	 * injection events, per cylinder
 	 */
 	InjectionEvent elements[MAX_INJECTION_OUTPUT_COUNT];
-	bool isReady;
-
-private:
-	void clear();
+	bool isReady = false;
 };
 
 class AngleBasedEvent {

firmware/controllers/engine_cycle/fuel_schedule.cpp

@@ -14,14 +14,13 @@ EXTERN_ENGINE;
 #if EFI_ENGINE_CONTROL
 
 FuelSchedule::FuelSchedule() {
-	clear();
 	for (int cylinderIndex = 0; cylinderIndex < MAX_INJECTION_OUTPUT_COUNT; cylinderIndex++) {
 		InjectionEvent *ev = &elements[cylinderIndex];
 		ev->ownIndex = cylinderIndex;
 	}
 }
 
-void FuelSchedule::clear() {
+void FuelSchedule::invalidate() {
 	isReady = false;
 }
 
@@ -142,19 +141,26 @@ bool FuelSchedule::addFuelEventsForCylinder(int i  DECLARE_ENGINE_PARAMETER_SUFF
 }
 
 void FuelSchedule::addFuelEvents(DECLARE_ENGINE_PARAMETER_SIGNATURE) {
-	clear();
-
 	for (int cylinderIndex = 0; cylinderIndex < CONFIG(specs.cylindersCount); cylinderIndex++) {
 		InjectionEvent *ev = &elements[cylinderIndex];
 		ev->ownIndex = cylinderIndex;  // todo: is this assignment needed here? we now initialize in constructor
 		bool result = addFuelEventsForCylinder(cylinderIndex PASS_ENGINE_PARAMETER_SUFFIX);
-		if (!result)
+		if (!result) {
+			invalidate();
 			return;
 		}
+	}
+
+	// We made it through all cylinders, mark the schedule as ready so it can be used
 	isReady = true;
 }
 
 void FuelSchedule::onTriggerTooth(size_t toothIndex, int rpm, efitick_t nowNt DECLARE_ENGINE_PARAMETER_SUFFIX) {
+	// Wait for schedule to be built - this happens the first time we get RPM
+	if (!isReady) {
+		return;
+	}
+
 	for (int i = 0; i < CONFIG(specs.cylindersCount); i++) {
 		elements[i].onTriggerTooth(toothIndex, rpm, nowNt);
 	}

firmware/controllers/math/engine_math.cpp

@@ -412,6 +412,9 @@ void prepareOutputSignals(DECLARE_ENGINE_PARAMETER_SIGNATURE) {
 	prepareIgnitionPinIndices(CONFIG(ignitionMode) PASS_ENGINE_PARAMETER_SUFFIX);
 
 	TRIGGER_WAVEFORM(prepareShape(&ENGINE(triggerCentral.triggerFormDetails) PASS_ENGINE_PARAMETER_SUFFIX));
+
+	// Fuel schedule may now be completely wrong, force a reset
+	ENGINE(injectionEvents).invalidate();
 }
 
 void setTimingRpmBin(float from, float to DECLARE_CONFIG_PARAMETER_SUFFIX) {

firmware/controllers/trigger/decoders/trigger_structure.cpp

@@ -418,9 +418,14 @@ void findTriggerPosition(TriggerWaveform *triggerShape,
 		return;
 	}
 
+	{
+		// This must happen under lock so that the tooth and offset don't get partially read and mismatched
+		chibios_rt::CriticalSectionLocker csl;
+
 		position->triggerEventIndex = triggerEventIndex;
 		position->angleOffsetFromTriggerEvent = angle - triggerEventAngle;
 	}
+}
 
 void TriggerWaveform::prepareShape(TriggerFormDetails *details DECLARE_ENGINE_PARAMETER_SUFFIX) {
 #if EFI_ENGINE_CONTROL && EFI_SHAFT_POSITION_INPUT