Add support for RX pull-up management

Author: manchoz

Diff for: cores/arduino/Serial.cpp

@@ -126,6 +126,15 @@ void UART::begin(unsigned long baudrate) {
 	}
 }
 
+void UART::begin(unsigned long baudrate, uint16_t config, bool no_rx_pullup) {
+	begin(baudrate, config);
+#if defined(SET_GPIO_PULL_FUNCTION)
+	if (no_rx_pullup) {
+		SET_GPIO_PULL_FUNCTION(_rx, NO_PULL);
+	}
+#endif
+}
+
 void UART::on_rx() {
 #if defined(SERIAL_CDC)
 	if (is_usb) {

Diff for: cores/arduino/Serial.h

@@ -45,6 +45,7 @@ class UART : public HardwareSerial {
 		}
 		void begin(unsigned long);
 		void begin(unsigned long baudrate, uint16_t config);
+		void begin(unsigned long baudrate, uint16_t config, bool no_rx_pullup);
 		void end();
 		int available(void);
 		int peek(void);

Diff for: variants/OPTA/pins_arduino.h

@@ -193,4 +193,22 @@ void _ontouch1200bps_();
 
 #define USB_MAX_POWER	(500)
 
+static GPIO_TypeDef * const GPIO_PORT[] = {
+    GPIOA,
+    GPIOB,
+    GPIOC,
+    GPIOD,
+    GPIOE,
+    GPIOF,
+    GPIOG,
+    GPIOH,
+    GPIOI,
+    GPIOJ,
+    GPIOK,
+};
+
+#include "pin_device.h"
+#define SET_GPIO_PULL_FUNCTION(x, y)        LL_GPIO_SetPinPull(GPIO_PORT[STM_PORT(x)], ll_pin_defines[STM_PIN(x)], y)
+#define NO_PULL         LL_GPIO_PULL_NO 
+
 #endif //__PINS_ARDUINO__