Fixes UART pin setting + adds CTS/RTS HW Flow Control (#6272)

* fixes setPins and begin to keep rx/tx unmodified

* adds Hardware Flow Control mode and CTS/RTS pin setting

* adds Hardware Flow Control mode and CTS/RTS pin setting

* adds Hardware Flow Control mode and CTS/RTS pin setting

* adds Hardware Flow Control mode and CTS/RTS pin setting

* Code Review

cores/esp32/HardwareSerial.cpp

@@ -6,6 +6,7 @@
 #include "pins_arduino.h"
 #include "HardwareSerial.h"
 #include "soc/soc_caps.h"
+#include "driver/uart.h"
 
 #ifndef SOC_RX0
 #if CONFIG_IDF_TARGET_ESP32
@@ -114,7 +115,6 @@ void serialEventRun(void)
 }
 #endif
 
-
 HardwareSerial::HardwareSerial(int uart_nr) : _uart_nr(uart_nr), _uart(NULL), _rxBufferSize(256) {}
 
 void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, int8_t txPin, bool invert, unsigned long timeout_ms, uint8_t rxfifo_full_thrhd)
@@ -123,28 +123,39 @@ void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, in
         log_e("Serial number is invalid, please use numers from 0 to %u", SOC_UART_NUM - 1);
         return;
     }
+
+    // First Time or after end() --> set default Pins
+    if (!uartIsDriverInstalled(_uart)) {
+        switch (_uart_nr) {
+            case UART_NUM_0:
+                rxPin = rxPin < 0 ? SOC_RX0 : rxPin;
+                txPin = txPin < 0 ? SOC_TX0 : txPin;
+            break;
+#if SOC_UART_NUM > 1                   // may save some flash bytes...
+            case UART_NUM_1:
+                rxPin = rxPin < 0 ? RX1 : rxPin;
+                txPin = txPin < 0 ? TX1 : txPin;
+            break;
+#endif
+#if SOC_UART_NUM > 2                   // may save some flash bytes...
+            case UART_NUM_2:
+                rxPin = rxPin < 0 ? RX2 : rxPin;
+                txPin = txPin < 0 ? TX2 : txPin;
+            break;
+#endif
+            default:
+                log_e("Bad UART Number");
+                return;
+        }
+    }
+
     if(_uart) {
         // in this case it is a begin() over a previous begin() - maybe to change baud rate
         // thus do not disable debug output
         end(false);
     }
-    if(_uart_nr == 0 && rxPin < 0 && txPin < 0) {
-        rxPin = SOC_RX0;
-        txPin = SOC_TX0;
-    }
-#if SOC_UART_NUM > 1
-    if(_uart_nr == 1 && rxPin < 0 && txPin < 0) {
-        rxPin = RX1;
-        txPin = TX1;
-    }
-#endif
-#if SOC_UART_NUM > 2
-    if(_uart_nr == 2 && rxPin < 0 && txPin < 0) {
-        rxPin = RX2;
-        txPin = TX2;
-    }
-#endif
 
+    // IDF UART driver keeps Pin setting on restarting. Negative Pin number will keep it unmodified.
     _uart = uartBegin(_uart_nr, baud ? baud : 9600, config, rxPin, txPin, _rxBufferSize, invert, rxfifo_full_thrhd);
     if (!baud) {
         // using baud rate as zero, forces it to try to detect the current baud rate in place
@@ -280,9 +291,16 @@ void HardwareSerial::setRxInvert(bool invert)
     uartSetRxInvert(_uart, invert);
 }
 
-void HardwareSerial::setPins(uint8_t rxPin, uint8_t txPin)
+// negative Pin value will keep it unmodified
+void HardwareSerial::setPins(int8_t rxPin, int8_t txPin, int8_t ctsPin, int8_t rtsPin)
 {
-    uartSetPins(_uart, rxPin, txPin);
+    uartSetPins(_uart, rxPin, txPin, ctsPin, rtsPin);
+}
+
+// Enables or disables Hardware Flow Control using RTS and/or CTS pins (must use setAllPins() before)
+void HardwareSerial::setHwFlowCtrlMode(uint8_t mode, uint8_t threshold)
+{
+    uartSetHwFlowCtrlMode(_uart, mode, threshold);
 }
 
 size_t HardwareSerial::setRxBufferSize(size_t new_size) {

cores/esp32/HardwareSerial.h

@@ -107,7 +107,13 @@ public:
     void setDebugOutput(bool);
     
     void setRxInvert(bool);
-    void setPins(uint8_t rxPin, uint8_t txPin);
+
+    // Negative Pin Number will keep it unmodified, thus this function can set individual pins
+    // SetPins shall be called after Serial begin()
+    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
+
     size_t setRxBufferSize(size_t new_size);
 
 protected:

cores/esp32/esp32-hal-uart.c

@@ -155,15 +155,27 @@ bool uartIsDriverInstalled(uart_t* uart)
     return false;
 }
 
-void uartSetPins(uart_t* uart, uint8_t rxPin, uint8_t txPin)
+// Valid pin UART_PIN_NO_CHANGE is defined to (-1)
+// Negative Pin Number will keep it unmodified, thus this function can set individual pins
+void uartSetPins(uart_t* uart, int8_t rxPin, int8_t txPin, int8_t ctsPin, int8_t rtsPin)
 {
-    if(uart == NULL || rxPin >= SOC_GPIO_PIN_COUNT || txPin >= SOC_GPIO_PIN_COUNT) {
+    if(uart == NULL) {
         return;
     }
     UART_MUTEX_LOCK();
-    ESP_ERROR_CHECK(uart_set_pin(uart->num, txPin, rxPin, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE)); 
+    // IDF uart_set_pin() will issue necessary Error Message and take care of all GPIO Number validation.
+    uart_set_pin(uart->num, txPin, rxPin, ctsPin, rtsPin); 
     UART_MUTEX_UNLOCK();  
+}
 
+// 
+void uartSetHwFlowCtrlMode(uart_t *uart, uint8_t mode, uint8_t threshold) {
+    if(uart == NULL) {
+        return;
+    }
+    // IDF will issue corresponding error message when mode or threshold are wrong and prevent crashing
+    // IDF will check (mode > HW_FLOWCTRL_CTS_RTS || threshold >= SOC_UART_FIFO_LEN)
+    uart_set_hw_flow_ctrl(uart->num, (uart_hw_flowcontrol_t) mode, threshold);
 }
 
 
@@ -173,10 +185,6 @@ uart_t* uartBegin(uint8_t uart_nr, uint32_t baudrate, uint32_t config, int8_t rx
         return NULL;
     }
 
-    if(rxPin == -1 && txPin == -1) {
-        return NULL;
-    }
-
     uart_t* uart = &_uart_bus_array[uart_nr];
 
     if (uart_is_driver_installed(uart_nr)) {

cores/esp32/esp32-hal-uart.h

@@ -48,6 +48,14 @@ extern "C" {
 #define SERIAL_7O2 0x800003b
 #define SERIAL_8O2 0x800003f
 
+// These are Hardware Flow Contol possible usage
+// equivalent to UDF enum uart_hw_flowcontrol_t from 
+// https://github.com/espressif/esp-idf/blob/master/components/hal/include/hal/uart_types.h#L75-L81
+#define HW_FLOWCTRL_DISABLE   0x0       // disable HW Flow Control
+#define HW_FLOWCTRL_RTS       0x1       // use only RTS PIN for HW Flow Control
+#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
+
 struct uart_struct_t;
 typedef struct uart_struct_t uart_t;
 
@@ -76,7 +84,12 @@ void uartSetDebug(uart_t* uart);
 int uartGetDebug();
 
 bool uartIsDriverInstalled(uart_t* uart);
-void uartSetPins(uart_t* uart, uint8_t rxPin, uint8_t txPin);
+
+// Negative Pin Number will keep it unmodified, thus this function can set individual pins
+void uartSetPins(uart_t* uart, int8_t rxPin, int8_t txPin, int8_t ctsPin, int8_t rtsPin);
+
+// 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);
 
 void uartStartDetectBaudrate(uart_t *uart);
 unsigned long uartDetectBaudrate(uart_t *uart);