fix: PXX1 external module timings (#3941)

radio/src/boards/generic_stm32/module_ports.cpp

@@ -520,6 +520,10 @@ const etx_module_t _sport_module = {
 
 #endif // SPORT_UPDATE_PWR_GPIO
 
+#if !defined(RADIO_X10E)
+uint32_t __pxx1_get_inverter_comp() { return 1; }
+#endif
+
 void boardInitModulePorts()
 {
   _sport_direction_init();

radio/src/targets/common/arm/stm32/stm32_softserial_driver.cpp

@@ -313,6 +313,8 @@ static void _conv_byte_8n1(stm32_softserial_tx_state* st, uint8_t b)
 #define PXX1_BIT_ZERO  16 /* 0 = 16us */
 #define PXX1_BIT_ONE   24 /* 1 = 24us */
 
+__attribute__ ((weak)) uint32_t __pxx1_get_inverter_comp() { return 0; }
+
 static void _conv_byte_pxx1(stm32_softserial_tx_state* st, uint8_t b)
 {
   uint32_t bits = st->serial_size < 8 ? st->serial_size : 8;
@@ -360,7 +362,7 @@ static void* stm32_softserial_tx_init(void* hw_def, const etx_serial_init* param
     freq = PXX1_FREQ;
     polarity = false;
     ocmode = LL_TIM_OCMODE_FORCED_INACTIVE;
-    cmp_val = PXX1_PWM_ON;
+    cmp_val = PXX1_PWM_ON + __pxx1_get_inverter_comp();
     break;
 
   default:
@@ -483,7 +485,7 @@ static void stm32_softserial_tx_send_buffer(void* ctx, const uint8_t* data, uint
   // dirty hack...
   if (st->conv_byte == _conv_byte_pxx1) {
     ocmode = LL_TIM_OCMODE_PWM1;
-    cmp_val = PXX1_PWM_ON;
+    cmp_val = PXX1_PWM_ON + __pxx1_get_inverter_comp();
   }
 
   stm32_pulse_start_dma_req(timer, pulses, length, ocmode, cmp_val);

radio/src/targets/common/arm/stm32/stm32_softserial_driver.h

@@ -105,3 +105,7 @@ struct stm32_softserial_tx_port {
 #define REF_STM32_SOFTSERIAL_PORT(p) ((void*)& p ## _STM32Softserial)
 
 extern const etx_serial_driver_t STM32SoftSerialTxDriver;
+
+// This is defined as a weak symbol to allow stretching the prelude part
+// of PXX1 pulses to an acceptable length
+uint32_t __pxx1_get_inverter_comp();