feat(uart): support UART Tx Rx invert function

This enables UART Tx and Rx invert function on STM32 families that support it.

In order to enable Tx and Rx invert, call respectively:

```c++
Serial1.setTxInvert();
Serial1.setRxInvert();
```

Fixes: #1160 #2669
See also: #1418

Signed-off-by: Andrew Yong <me@ndoo.sg>

Author: ndoo

cores/arduino/HardwareSerial.cpp

@@ -446,7 +446,7 @@ void HardwareSerial::begin(unsigned long baud, byte config)
       break;
   }
 
-  uart_init(&_serial, (uint32_t)baud, databits, parity, stopbits);
+  uart_init(&_serial, (uint32_t)baud, databits, parity, stopbits, _rx_invert, _tx_invert);
   enableHalfDuplexRx();
   uart_attach_rx_callback(&_serial, _rx_complete_irq);
 }
@@ -668,4 +668,14 @@ void HardwareSerial::enableHalfDuplexRx(void)
   }
 }
 
+void HardwareSerial::setRxInvert(void)
+{
+  _rx_invert = true;
+}
+
+void HardwareSerial::setTxInvert(void)
+{
+  _tx_invert = true;
+}
+
 #endif // HAL_UART_MODULE_ENABLED && !HAL_UART_MODULE_ONLY

cores/arduino/HardwareSerial.h

@@ -95,6 +95,8 @@ class HardwareSerial : public Stream {
   protected:
     // Has any byte been written to the UART since begin()
     bool _written;
+    bool _rx_invert;
+    bool _tx_invert;
 
     // Don't put any members after these buffers, since only the first
     // 32 bytes of this struct can be accessed quickly using the ldd
@@ -165,6 +167,11 @@ class HardwareSerial : public Stream {
     bool isHalfDuplex(void) const;
     void enableHalfDuplexRx(void);
 
+    // Enable HW Rx/Tx inversion
+    // This needs to be done before the call to begin()
+    void setRxInvert(void);
+    void setTxInvert(void);
+
     friend class STM32LowPower;
 
     // Interrupt handlers

libraries/SrcWrapper/inc/uart.h

@@ -254,7 +254,7 @@ struct serial_s {
 
 /* Exported macro ------------------------------------------------------------*/
 /* Exported functions ------------------------------------------------------- */
-void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t parity, uint32_t stopbits);
+void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t parity, uint32_t stopbits, uint8_t rx_invert, uint8_t tx_invert);
 void uart_deinit(serial_t *obj);
 #if defined(HAL_PWR_MODULE_ENABLED) && (defined(UART_IT_WUF) || defined(LPUART1_BASE))
 void uart_config_lowpower(serial_t *obj);

libraries/SrcWrapper/src/stm32/uart.c

@@ -115,7 +115,7 @@ serial_t *get_serial_obj(UART_HandleTypeDef *huart)
   * @param  obj : pointer to serial_t structure
   * @retval None
   */
-void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t parity, uint32_t stopbits)
+void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t parity, uint32_t stopbits, uint8_t rx_invert, uint8_t tx_invert)
 {
   if (obj == NULL) {
     return;
@@ -408,10 +408,20 @@ void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t par
   huart->Init.HwFlowCtl    = flow_control;
   huart->Init.OverSampling = UART_OVERSAMPLING_16;
 #if defined(UART_ADVFEATURE_SWAP_INIT)
-  huart->AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_SWAP_INIT;
+  huart->AdvancedInit.AdvFeatureInit |= UART_ADVFEATURE_SWAP_INIT;
   huart->AdvancedInit.Swap = pin_swap;
 #elif defined(UART_ADVFEATURE_NO_INIT)
-  huart->AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
+  huart->AdvancedInit.AdvFeatureInit |= UART_ADVFEATURE_NO_INIT;
+#endif
+#if defined(UART_ADVFEATURE_RXINVERT_INIT)
+  if (rx_invert) {
+    huart->AdvancedInit.AdvFeatureInit |= UART_ADVFEATURE_RXINVERT_INIT;
+  }
+#endif
+#if defined(UART_ADVFEATURE_TXINVERT_INIT)
+  if (tx_invert) {
+    huart->AdvancedInit.AdvFeatureInit |= UART_ADVFEATURE_TXINVERT_INIT;
+  }
 #endif
 #ifdef UART_ONE_BIT_SAMPLE_DISABLE
   huart->Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
@@ -812,7 +822,7 @@ void uart_debug_init(void)
     serial_debug.pin_tx = pinmap_pin(DEBUG_UART, PinMap_UART_TX);
 #endif
     /* serial_debug.pin_rx set by default to NC to configure in half duplex mode */
-    uart_init(&serial_debug, DEBUG_UART_BAUDRATE, UART_WORDLENGTH_8B, UART_PARITY_NONE, UART_STOPBITS_1);
+    uart_init(&serial_debug, DEBUG_UART_BAUDRATE, UART_WORDLENGTH_8B, UART_PARITY_NONE, UART_STOPBITS_1, false, false);
   }
 }