Bugfix/detect baudrate (#3188)

* Expose uartStartDetectBaudrate(uart_t *) in esp32-hal-uart.h and call it from HardwareSerial::begin() if baudrate detection is requested (by passing a baudrate of 0) to solve baudrate detection problems

* Avoid a division by zero error in uartGetBaudRate()

cores/esp32/HardwareSerial.cpp

@@ -55,6 +55,7 @@ void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, in
     _uart = uartBegin(_uart_nr, baud ? baud : 9600, config, rxPin, txPin, 256, invert);
 
     if(!baud) {
+        uartStartDetectBaudrate(_uart);
         time_t startMillis = millis();
         unsigned long detectedBaudRate = 0;
         while(millis() - startMillis < timeout_ms && !(detectedBaudRate = uartDetectBaudrate(_uart))) {

cores/esp32/esp32-hal-uart.c

@@ -401,7 +401,12 @@ uint32_t uartGetBaudRate(uart_t* uart)
     if(uart == NULL) {
         return 0;
     }
+
     uint32_t clk_div = (uart->dev->clk_div.div_int << 4) | (uart->dev->clk_div.div_frag & 0x0F);
+    if(!clk_div) {
+        return 0;
+    }
+
     return ((getApbFrequency()<<4)/clk_div);
 }
 
@@ -522,6 +527,14 @@ unsigned long uartBaudrateDetect(uart_t *uart, bool flg)
  * detected calling uartBadrateDetect(). The raw baudrate is computed using the UART_CLK_FREQ. The raw baudrate is 
  * rounded to the closed real baudrate.
 */
+void uartStartDetectBaudrate(uart_t *uart) {
+  if(!uart) return;
+
+  uart->dev->auto_baud.glitch_filt = 0x08;
+  uart->dev->auto_baud.en = 0;
+  uart->dev->auto_baud.en = 1;
+}
+
 unsigned long
 uartDetectBaudrate(uart_t *uart)
 {

cores/esp32/esp32-hal-uart.h

@@ -72,6 +72,7 @@ size_t uartResizeRxBuffer(uart_t* uart, size_t new_size);
 void uartSetDebug(uart_t* uart);
 int uartGetDebug();
 
+void uartStartDetectBaudrate(uart_t *uart);
 unsigned long uartDetectBaudrate(uart_t *uart);
 
 bool uartRxActive(uart_t* uart);