Added argument to HardwareSerial.begin to specify whether the logic levels of...

Added argument to HardwareSerial.begin to specify whether the logic levels of the UART rx and tx lines should be inverted (#719)

cores/esp32/HardwareSerial.cpp

@@ -9,7 +9,7 @@ HardwareSerial Serial(0);
 
 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)
+void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, int8_t txPin, bool invert)
 {
     if(0 > _uart_nr || _uart_nr > 2) {
         log_e("Serial number is invalid, please use 0, 1 or 2");
@@ -30,7 +30,7 @@ void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, in
         rxPin = 16;
         txPin = 17;
     }
-    _uart = uartBegin(_uart_nr, baud, config, rxPin, txPin, 256, false);
+    _uart = uartBegin(_uart_nr, baud, config, rxPin, txPin, 256, invert);
 }
 
 void HardwareSerial::end()

cores/esp32/HardwareSerial.h

@@ -37,7 +37,7 @@ 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);
+    void begin(unsigned long baud, uint32_t config=SERIAL_8N1, int8_t rxPin=-1, int8_t txPin=-1, bool invert=false);
     void end();
     int available(void);
     int peek(void);