Configurable IRQ prio and read first in ISR

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

@@ -67,6 +67,7 @@ static const stm32_usart_t extmoduleUSART = {
   .GPIOx = EXTMODULE_TX_GPIO,
   .pinInit = &extmoduleUSART_PinDef,
   .IRQn = EXTMODULE_USART_IRQn,
+  .IRQ_Prio = EXTMODULE_USART_IRQ_PRIORITY,
   .DMAx = EXTMODULE_USART_TX_DMA,
   .DMA_Stream = EXTMODULE_USART_TX_DMA_STREAM_LL,
   .DMA_Channel = EXTMODULE_USART_TX_DMA_CHANNEL,

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

@@ -24,6 +24,8 @@
 #include <stdint.h>
 #include "hal/serial_driver.h"
 
+#define EXTMODULE_USART_IRQ_PRIORITY 6
+
 // Callbacks using intmoduleFifo
 void extmoduleFifoReceive(uint8_t data);
 void extmoduleFifoError();

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

@@ -78,6 +78,7 @@ static const stm32_usart_t intmoduleUSART = {
   .GPIOx = INTMODULE_GPIO,
   .pinInit = &intmoduleUSART_PinDef,
   .IRQn = INTMODULE_USART_IRQn,
+  .IRQ_Prio = INTMODULE_USART_IRQ_PRIORITY,
   .DMAx = INTMODULE_DMA,
   .DMA_Stream = INTMODULE_DMA_STREAM_LL,
   .DMA_Channel = INTMODULE_DMA_CHANNEL,

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

@@ -24,6 +24,8 @@
 #include <stdint.h>
 #include "hal/serial_driver.h"
 
+#define INTMODULE_USART_IRQ_PRIORITY 6
+
 // Callbacks using intmoduleFifo
 void intmoduleFifoReceive(uint8_t data);
 void intmoduleFifoError();

radio/src/targets/common/arm/stm32/stm32_usart_driver.cpp

@@ -82,7 +82,7 @@ void stm32_usart_init(const stm32_usart_t* usart, const etx_serial_init* params)
 
   if (!usart->DMAx || params->rx_enable) {
     // TODO: configurable priority ???
-    NVIC_SetPriority(usart->IRQn, 6);
+    NVIC_SetPriority(usart->IRQn, usart->IRQ_Prio);
     NVIC_EnableIRQ(usart->IRQn);
   }
 }
@@ -107,6 +107,7 @@ void stm32_usart_deinit(const stm32_usart_t* usart)
 
 void stm32_usart_send_byte(const stm32_usart_t* usart, uint8_t byte)
 {
+  // TODO: split into 2 steps to avoid blocking on send
   while (!LL_USART_IsActiveFlag_TXE(usart->USARTx));
   LL_USART_TransmitData8(usart->USARTx, byte);
 }
@@ -177,18 +178,7 @@ void stm32_usart_isr(const stm32_usart_t* usart, etx_serial_callbacks_t* cb)
 {
   uint32_t status = LL_USART_ReadReg(usart->USARTx, SR);
 
-  // IRQ based send: TXE IRQ is enabled only during transfer
-  if (LL_USART_IsEnabledIT_TXE(usart->USARTx) && (status & LL_USART_SR_TXE)) {
-
-    uint8_t data;
-    if (cb->on_send && cb->on_send(data)) {
-      LL_USART_TransmitData8(usart->USARTx, data);
-    } else {
-      LL_USART_DisableIT_TXE(usart->USARTx);
-    }
-  }
-
-  // Receive
+  // Receive: do it first as it is more time critical
   if (LL_USART_IsEnabledIT_TXE(usart->USARTx)) {
 
     // Drain RX
@@ -209,4 +199,15 @@ void stm32_usart_isr(const stm32_usart_t* usart, etx_serial_callbacks_t* cb)
       status = LL_USART_ReadReg(usart->USARTx, SR);
     }
   }
+
+  // IRQ based send: TXE IRQ is enabled only during transfer
+  if (LL_USART_IsEnabledIT_TXE(usart->USARTx) && (status & LL_USART_SR_TXE)) {
+
+    uint8_t data;
+    if (cb->on_send && cb->on_send(data)) {
+      LL_USART_TransmitData8(usart->USARTx, data);
+    } else {
+      LL_USART_DisableIT_TXE(usart->USARTx);
+    }
+  }
 }

radio/src/targets/common/arm/stm32/stm32_usart_driver.h

@@ -31,7 +31,10 @@ struct stm32_usart_t {
     USART_TypeDef*             USARTx;
     GPIO_TypeDef*              GPIOx;
     const LL_GPIO_InitTypeDef* pinInit;
+
+    // USART IRQ
     IRQn_Type                  IRQn;
+    uint8_t                    IRQ_Prio;
 
     // TX DMA defs
     DMA_TypeDef*               DMAx;