fix: Corrupt data using soft serial driver (#3329)

* restore bit start detection IRQ for soft serial

* restore bit start detection IRQ for softserial (target Taranis and Horus)

* target Taranis: EXTI9_5 is a shared interrupt for Rotary Encoder and Heartbeat for X7, X7-ACCESS und TPRO radios. Changed IRQ priority accordingly

* fix crashes where the heartbeat ISR running at interrupt priorities higher than 5 interferes with FreeRTOS calls made from within the heartbeat ISR.

* changed mixer scheduler timer initialization to allow for software generated update events to avoid freeRTOS calls from now prio 0 heartbeat ISR.

* resolved review feedback: using defines for IRQ prio settings

* following review by @raphaelcoeffic:

- new function void mixerSchedulerSoftTrigger() (to be called by heartbeat driver)
- defines in hal.h for targets horus and taranis

* following @raphaelcoeffics review

- changed all but telemetry EXIT IRQ (soft serial) definition back to their original state and added define to override EXIT IRQ (soft serial) prio

radio/src/mixer_scheduler.h

@@ -40,9 +40,6 @@ void mixerSchedulerStart();
 // Stop the scheduler timer
 void mixerSchedulerStop();
 
-// Set the timer counter to 0
-void mixerSchedulerResetTimer();
-
 // Set the scheduling period for a given module
 void mixerSchedulerSetPeriod(uint8_t moduleIdx, uint16_t periodUs);
 
@@ -55,6 +52,9 @@ void mixerSchedulerEnableTrigger();
 // Disable the timer trigger
 void mixerSchedulerDisableTrigger();
 
+// Trigger mixer from heartbeat interrupt 
+void mixerSchedulerSoftTrigger();
+
 // Fetch the current scheduling period
 uint16_t getMixerSchedulerPeriod();
 
@@ -66,14 +66,14 @@ void mixerSchedulerISRTrigger();
 #define mixerSchedulerInit()
 #define mixerSchedulerStart()
 #define mixerSchedulerStop()
-#define mixerSchedulerResetTimer()
 #define mixerSchedulerSetPeriod(m,p) ((void)(p))
 #define mixerSchedulerGetPeriod(m) ((uint16_t)MIXER_SCHEDULER_DEFAULT_PERIOD_US)
-#define mixerSchedulerClearTrigger()
 
 #define mixerSchedulerEnableTrigger()
 #define mixerSchedulerDisableTrigger()
 
+#define mixerSchedulerSoftTrigger()
+
 #define getMixerSchedulerPeriod() (MIXER_SCHEDULER_DEFAULT_PERIOD_US)
 #define mixerSchedulerISRTrigger()
 

radio/src/targets/common/arm/stm32/heartbeat_driver.cpp

@@ -41,8 +41,7 @@ static void trigger_intmodule_heartbeat()
   heartbeatCapture.count++;
 #endif
 
-  mixerSchedulerResetTimer();
-  mixerSchedulerISRTrigger();
+  mixerSchedulerSoftTrigger();
 }
 
 void init_intmodule_heartbeat()

radio/src/targets/common/arm/stm32/mixer_scheduler_driver.cpp

@@ -30,13 +30,11 @@
 void mixerSchedulerStart()
 {
   MIXER_SCHEDULER_TIMER->CR1 &= ~TIM_CR1_CEN;
-
-  MIXER_SCHEDULER_TIMER->CR1   = TIM_CR1_URS; // do not generate interrupt on soft update
   MIXER_SCHEDULER_TIMER->PSC   = MIXER_SCHEDULER_TIMER_FREQ / 1000000 - 1; // 1uS (1Mhz)
   MIXER_SCHEDULER_TIMER->CCER  = 0;
   MIXER_SCHEDULER_TIMER->CCMR1 = 0;
   MIXER_SCHEDULER_TIMER->ARR   = getMixerSchedulerPeriod() - 1;
-  MIXER_SCHEDULER_TIMER->EGR   = TIM_EGR_UG;   // reset timer
+  MIXER_SCHEDULER_TIMER->CNT   = 0;   // reset counter
 
   NVIC_EnableIRQ(MIXER_SCHEDULER_TIMER_IRQn);
   NVIC_SetPriority(MIXER_SCHEDULER_TIMER_IRQn,
@@ -53,13 +51,6 @@ void mixerSchedulerStop()
   NVIC_DisableIRQ(MIXER_SCHEDULER_TIMER_IRQn);
 }
 
-void mixerSchedulerResetTimer()
-{
-  mixerSchedulerDisableTrigger();
-  MIXER_SCHEDULER_TIMER->CNT = 0;
-  mixerSchedulerEnableTrigger();
-}
-
 void mixerSchedulerEnableTrigger()
 {
   MIXER_SCHEDULER_TIMER->DIER |= TIM_DIER_UIE; // enable interrupt
@@ -70,6 +61,15 @@ void mixerSchedulerDisableTrigger()
   MIXER_SCHEDULER_TIMER->DIER &= ~TIM_DIER_UIE; // disable interrupt
 }
 
+void mixerSchedulerSoftTrigger() {
+  // Generate a timer update event (TIM_EGR_UG) to reload the Prescaler and the repetition 
+  // counter value immediately to avoid making FreeRTOS calls within this ISR:
+  // - fires MIXER_SCHEDULER_TIMER interrupt after returning from this ISR
+  // - MIXER_SCHEDULER_TIMER_IRQHandler(void) takes care of making FreeRTOS calls
+  //   to ensure switching to highest priority task.
+  MIXER_SCHEDULER_TIMER->EGR = TIM_EGR_UG; 
+}
+
 extern "C" void MIXER_SCHEDULER_TIMER_IRQHandler(void)
 {
   MIXER_SCHEDULER_TIMER->SR &= ~TIM_SR_UIF; // clear flag

radio/src/targets/horus/hal.h

@@ -28,6 +28,8 @@
 #define TIMER_MULT_APB1                 2
 #define TIMER_MULT_APB2                 2
 
+#define TELEMETRY_EXTI_PRIO             0 // required for soft serial
+
 // Keys
 #define KEYS_RCC_AHB1Periph             (RCC_AHB1Periph_GPIOB | RCC_AHB1Periph_GPIOC | RCC_AHB1Periph_GPIOD | RCC_AHB1Periph_GPIOE | RCC_AHB1Periph_GPIOG | RCC_AHB1Periph_GPIOH | RCC_AHB1Periph_GPIOI | RCC_AHB1Periph_GPIOJ)
 #if defined(PCBX12S)
@@ -521,8 +523,10 @@
 // TELEMETRY_EXTI IRQ
 #if !defined(USE_EXTI9_5_IRQ)
   #define USE_EXTI9_5_IRQ
-  #define EXTI9_5_IRQ_Priority 5
 #endif
+// overwrite priority
+#undef EXTI9_5_IRQ_Priority
+#define EXTI9_5_IRQ_Priority            TELEMETRY_EXTI_PRIO
 
 #define TELEMETRY_TIMER                 TIM11
 #define TELEMETRY_TIMER_IRQn            TIM1_TRG_COM_TIM11_IRQn

radio/src/targets/taranis/hal.h

@@ -35,6 +35,8 @@
 #define TIMER_MULT_APB1                 2
 #define TIMER_MULT_APB2                 2
 
+#define TELEMETRY_EXTI_PRIO             0 // required for soft serial
+
 // Keys
 #if defined(PCBX9E)
   #define KEYS_GPIO_REG_MENU            GPIOD->IDR
@@ -1962,8 +1964,10 @@
 // TELEMETRY_EXTI IRQ
 #if !defined(USE_EXTI9_5_IRQ)
   #define USE_EXTI9_5_IRQ
-  #define EXTI9_5_IRQ_Priority 5
 #endif
+// overwrite priority
+#undef EXTI9_5_IRQ_Priority
+#define EXTI9_5_IRQ_Priority            TELEMETRY_EXTI_PRIO
 
 #define TELEMETRY_TIMER                 TIM11
 #define TELEMETRY_TIMER_PRESCALER       ()