feat(uart): allows the board pins_arduino.h to define other uart pins

Author: SuGlider

cores/esp32/HardwareSerial.cpp

@@ -349,8 +349,34 @@ void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, in
 #endif
         }
         break;
+#endif
+#if SOC_UART_HP_NUM > 3  // may save some flash bytes...
+      case UART_NUM_3:
+        if (rxPin < 0 && txPin < 0) {
+          // do not change RX2/TX2 if it has already been set before
+#ifdef RX3
+          rxPin = _rxPin < 0 ? (int8_t)RX3 : _rxPin;
+#endif
+#ifdef TX3
+          txPin = _txPin < 0 ? (int8_t)TX3 : _txPin;
+#endif
+        }
+        break;
 #endif
     }
+#if SOC_UART_HP_NUM > 4  // may save some flash bytes...
+      case UART_NUM_4:
+        if (rxPin < 0 && txPin < 0) {
+          // do not change RX2/TX2 if it has already been set before
+#ifdef RX4
+          rxPin = _rxPin < 0 ? (int8_t)RX4 : _rxPin;
+#endif
+#ifdef TX4
+          txPin = _txPin < 0 ? (int8_t)TX4 : _txPin;
+#endif
+        }
+        break;
+#endif
   }
 
   // if no RX/TX pins are defined, it will not start the UART driver