Added baudrate detection to esp32-hal-uart and HardwareSerial (espressif#1961)

* Added baudrate detection to esp32-hal-uart and HardwareSerial

* Solved compiler warning for uartResizeRxBuffer()

* Add unit to header variable name (timeout_ms)

* Reverting accidentally changed files to master

* Add small delay after baudrate detection

Author: Jeroen88

cores/esp32/HardwareSerial.cpp

@@ -30,7 +30,7 @@ HardwareSerial Serial2(2);
 
 HardwareSerial::HardwareSerial(int uart_nr) : _uart_nr(uart_nr), _uart(NULL) {}
 
-void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, int8_t txPin, bool invert)
+void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, int8_t txPin, bool invert, unsigned long timeout_ms)
 {
     if(0 > _uart_nr || _uart_nr > 2) {
         log_e("Serial number is invalid, please use 0, 1 or 2");
@@ -51,7 +51,26 @@ void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, in
         rxPin = RX2;
         txPin = TX2;
     }
-    _uart = uartBegin(_uart_nr, baud, config, rxPin, txPin, 256, invert);
+
+    _uart = uartBegin(_uart_nr, baud ? baud : 9600, config, rxPin, txPin, 256, invert);
+
+    if(!baud) {
+        time_t startMillis = millis();
+        unsigned long detectedBaudRate;
+        while(millis() - startMillis < timeout_ms && !(detectedBaudRate = uartDetectBaudrate(_uart))) {
+            yield();
+        }
+
+        end();
+
+        if(detectedBaudRate) {
+            delay(100); // Give some time...
+            _uart = uartBegin(_uart_nr, detectedBaudRate, config, rxPin, txPin, 256, invert);
+        } else {
+            log_e("Could not detect baudrate. Serial data at the port must be present within the timeout for detection to be possible");
+            _uart = NULL;
+        }
+    }
 }
 
 void HardwareSerial::end()

cores/esp32/HardwareSerial.h

@@ -22,6 +22,24 @@
  Modified 18 December 2014 by Ivan Grokhotkov (esp8266 platform support)
  Modified 31 March 2015 by Markus Sattler (rewrite the code for UART0 + UART1 support in ESP8266)
  Modified 25 April 2015 by Thomas Flayols (add configuration different from 8N1 in ESP8266)
+ Modified 13 October 2018 by Jeroen Döll (add baudrate detection)
+ Baudrate detection example usage (detection on Serial1):
+   void setup() {
+     Serial.begin(115200);
+     delay(100);
+     Serial.println();
+
+     Serial1.begin(0, SERIAL_8N1, -1, -1, true, 11000UL);  // Passing 0 for baudrate to detect it, the last parameter is a timeout in ms
+
+     unsigned long detectedBaudRate = Serial1.baudRate();
+     if(detectedBaudRate) {
+       Serial.printf("Detected baudrate is %lu\n", detectedBaudRate);
+     } else {
+       Serial.println("No baudrate detected, Serial1 will not work!");
+     }
+   }
+
+ Pay attention: the baudrate returned by baudRate() may be rounded, eg 115200 returns 115201
  */
 
 #ifndef HardwareSerial_h
@@ -37,7 +55,7 @@ class HardwareSerial: public Stream
 public:
     HardwareSerial(int uart_nr);
 
-    void begin(unsigned long baud, uint32_t config=SERIAL_8N1, int8_t rxPin=-1, int8_t txPin=-1, bool invert=false);
+    void begin(unsigned long baud, uint32_t config=SERIAL_8N1, int8_t rxPin=-1, int8_t txPin=-1, bool invert=false, unsigned long timeout_ms = 20000UL);
     void end();
     int available(void);
     int availableForWrite(void);

cores/esp32/esp32-hal-uart.c

@@ -242,7 +242,7 @@ void uartEnd(uart_t* uart)
 
 size_t uartResizeRxBuffer(uart_t * uart, size_t new_size) {
     if(uart == NULL) {
-        return;
+        return 0;
     }
 
     UART_MUTEX_LOCK();
@@ -455,3 +455,65 @@ int log_printf(const char *format, ...)
     }
     return len;
 }
+
+/*
+ * if enough pulses are detected return the minimum high pulse duration + minimum low pulse duration divided by two. 
+ * This equals one bit period. If flag is true the function return inmediately, otherwise it waits for enough pulses.
+ */
+unsigned long uartBaudrateDetect(uart_t *uart, bool flg)
+{
+    while(uart->dev->rxd_cnt.edge_cnt < 30) { // UART_PULSE_NUM(uart_num)
+        if(flg) return 0;
+        ets_delay_us(1000);
+    }
+
+    UART_MUTEX_LOCK();
+    unsigned long ret = ((uart->dev->lowpulse.min_cnt + uart->dev->highpulse.min_cnt) >> 1) + 12;
+    UART_MUTEX_UNLOCK();
+
+    return ret;
+}
+
+/*
+ * To start detection of baud rate with the uart the auto_baud.en bit needs to be cleared and set. The bit period is 
+ * detected calling uartBadrateDetect(). The raw baudrate is computed using the UART_CLK_FREQ. The raw baudrate is 
+ * rounded to the closed real baudrate.
+*/
+unsigned long
+uartDetectBaudrate(uart_t *uart)
+{
+    static bool uartStateDetectingBaudrate = false;
+
+    if(!uartStateDetectingBaudrate) {
+        uart->dev->auto_baud.glitch_filt = 0x08;
+        uart->dev->auto_baud.en = 0;
+        uart->dev->auto_baud.en = 1;
+        uartStateDetectingBaudrate = true;
+    }
+
+    unsigned long divisor = uartBaudrateDetect(uart, true);
+    if (!divisor) {
+        return 0;
+    }
+
+    uart->dev->auto_baud.en = 0;
+    uartStateDetectingBaudrate = false; // Initialize for the next round
+
+    unsigned long baudrate = UART_CLK_FREQ / divisor;
+
+    static const unsigned long default_rates[] = {300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 74880, 115200, 230400, 256000, 460800, 921600, 1843200, 3686400};
+
+    size_t i;
+    for (i = 1; i < sizeof(default_rates) / sizeof(default_rates[0]) - 1; i++)	// find the nearest real baudrate
+    {
+        if (baudrate <= default_rates[i])
+        {
+            if (baudrate - default_rates[i - 1] < default_rates[i] - baudrate) {
+                i--;
+            }
+            break;
+        }
+    }
+
+    return default_rates[i];
+}

cores/esp32/esp32-hal-uart.h

@@ -72,6 +72,8 @@ size_t uartResizeRxBuffer(uart_t* uart, size_t new_size);
 void uartSetDebug(uart_t* uart);
 int uartGetDebug();
 
+unsigned long uartDetectBaudrate(uart_t *uart);
+
 #ifdef __cplusplus
 }
 #endif