Implement Tx only Flush

cores/esp32/HardwareSerial.cpp

@@ -131,11 +131,16 @@ int HardwareSerial::read(void)
     return -1;
 }
 
-void HardwareSerial::flush()
+void HardwareSerial::flush(void)
 {
     uartFlush(_uart);
 }
 
+void HardwareSerial::flush(bool txOnly)
+{
+    uartFlushTxOnly(_uart, txOnly);
+}
+
 size_t HardwareSerial::write(uint8_t c)
 {
     uartWrite(_uart, c);

cores/esp32/HardwareSerial.h

@@ -63,6 +63,7 @@ class HardwareSerial: public Stream
     int peek(void);
     int read(void);
     void flush(void);
+    void flush( bool txOnly);
     size_t write(uint8_t);
     size_t write(const uint8_t *buffer, size_t size);
 

cores/esp32/esp32-hal-uart.c

@@ -327,24 +327,31 @@ void uartWriteBuf(uart_t* uart, const uint8_t * data, size_t len)
 }
 
 void uartFlush(uart_t* uart)
+{
+    uartFlushTxOnly(uart,false);
+}
+
+void uartFlushTxOnly(uart_t* uart, bool txOnly)
 {
     if(uart == NULL) {
         return;
     }
 
     UART_MUTEX_LOCK();
     while(uart->dev->status.txfifo_cnt || uart->dev->status.st_utx_out);
+
+    if( !txOnly ){
+        //Due to hardware issue, we can not use fifo_rst to reset uart fifo.
+        //See description about UART_TXFIFO_RST and UART_RXFIFO_RST in <<esp32_technical_reference_manual>> v2.6 or later.
 
-    //Due to hardware issue, we can not use fifo_rst to reset uart fifo.
-    //See description about UART_TXFIFO_RST and UART_RXFIFO_RST in <<esp32_technical_reference_manual>> v2.6 or later.
+        // we read the data out and make `fifo_len == 0 && rd_addr == wr_addr`.
+        while(uart->dev->status.rxfifo_cnt != 0 || (uart->dev->mem_rx_status.wr_addr != uart->dev->mem_rx_status.rd_addr)) {
+            READ_PERI_REG(UART_FIFO_REG(uart->num));
+        }
 
-    // we read the data out and make `fifo_len == 0 && rd_addr == wr_addr`.
-    while(uart->dev->status.rxfifo_cnt != 0 || (uart->dev->mem_rx_status.wr_addr != uart->dev->mem_rx_status.rd_addr)) {
-        READ_PERI_REG(UART_FIFO_REG(uart->num));
+        xQueueReset(uart->queue);
     }
-
-    xQueueReset(uart->queue);
-
+
     UART_MUTEX_UNLOCK();
 }
 

cores/esp32/esp32-hal-uart.h

@@ -63,6 +63,7 @@ void uartWrite(uart_t* uart, uint8_t c);
 void uartWriteBuf(uart_t* uart, const uint8_t * data, size_t len);
 
 void uartFlush(uart_t* uart);
+void uartFlushTxOnly(uart_t* uart, bool txOnly );
 
 void uartSetBaudRate(uart_t* uart, uint32_t baud_rate);
 uint32_t uartGetBaudRate(uart_t* uart);