Added setMode function to set the esp32 uart mode

Used to set the esp32 uart mode for use with RS485 Half Duplex and the auto RTS pin mode. This will set/clear the RTS pin output to control the RE/DE pin on most RS485 chips.

cores/esp32/HardwareSerial.cpp

@@ -572,6 +572,16 @@ void HardwareSerial::setHwFlowCtrlMode(uint8_t mode, uint8_t threshold)
     uartSetHwFlowCtrlMode(_uart, mode, threshold);
 }
 
+// Sets the uart mode in the esp32 uart for use with RS485 modes (HwFlowCtrl must be disabled and RTS pin set)
+int HardwareSerial::setMode(uart_mode_t mode)
+{
+    if (_uart == 0)
+    {
+        return -1;
+    }
+    return uartSetMode(_uart, mode);
+}
+
 size_t HardwareSerial::setRxBufferSize(size_t new_size) {
 
     if (_uart) {

cores/esp32/HardwareSerial.h

@@ -164,7 +164,8 @@ class HardwareSerial: public Stream
     void setPins(int8_t rxPin, int8_t txPin, int8_t ctsPin = -1, int8_t rtsPin = -1);
     // Enables or disables Hardware Flow Control using RTS and/or CTS pins (must use setAllPins() before)
     void setHwFlowCtrlMode(uint8_t mode = HW_FLOWCTRL_CTS_RTS, uint8_t threshold = 64);   // 64 is half FIFO Length
-
+    // Used to set RS485 modes such as UART_MODE_RS485_HALF_DUPLEX for Auto RTS function on ESP32
+    int setMode(uint8_t mode);
     size_t setRxBufferSize(size_t new_size);
     size_t setTxBufferSize(size_t new_size);
 

cores/esp32/esp32-hal-uart.c

@@ -518,6 +518,17 @@ void uart_install_putc()
     }
 }
 
+// Routines that take care of UART mode in the HardwareSerial Class code
+// used to set UART_MODE_RS485_HALF_DUPLEX auto RTS for TXD for ESP32 chips
+int uartSetMode(uart_t *uart, uint8_t mode)
+{
+    if (uart == NULL || uart->num >= SOC_UART_NUM)
+    {
+        return -1;
+    }
+    return uart_set_mode(uart->num, mode);
+}
+
 void uartSetDebug(uart_t* uart)
 {
     if(uart == NULL || uart->num >= SOC_UART_NUM) {

cores/esp32/esp32-hal-uart.h

@@ -58,6 +58,15 @@ extern "C" {
 #define HW_FLOWCTRL_CTS       0x2       // use only CTS PIN for HW Flow Control
 #define HW_FLOWCTRL_CTS_RTS   0x3       // use both CTS and RTS PIN for HW Flow Control
 
+// These are Hardware Uart Modes possible usage
+// equivalent to UDF enum uart_mode_t from
+// https://github.com/espressif/esp-idf/blob/master/components/hal/include/hal/uart_types.h#L34-L40
+#define MODE_UART 0x00                   // mode: regular UART mode
+#define MODE_RS485_HALF_DUPLEX 0x01      // mode: half duplex RS485 UART mode control by RTS pin
+#define MODE_IRDA 0x02                   // mode: IRDA  UART mode
+#define MODE_RS485_COLLISION_DETECT 0x03 // mode: RS485 collision detection UART mode (used for test purposes)
+#define MODE_RS485_APP_CTRL 0x04
+
 struct uart_struct_t;
 typedef struct uart_struct_t uart_t;
 
@@ -99,6 +108,10 @@ void uartDetachPins(uart_t* uart, int8_t rxPin, int8_t txPin, int8_t ctsPin, int
 // Enables or disables HW Flow Control function -- needs also to set CTS and/or RTS pins
 void uartSetHwFlowCtrlMode(uart_t *uart, uint8_t mode, uint8_t threshold);
 
+// Used to set RS485 function -- needs to disable HW Flow Control and set RTS pin to use
+// RTS pin becomes RS485 half duplex RE/DE
+int uartSetMode(uart_t *uart, uint8_t mode);
+
 void uartStartDetectBaudrate(uart_t *uart);
 unsigned long uartDetectBaudrate(uart_t *uart);