🔧 USART6 for STM32, expand port range (#27262)

Marlin/Configuration.h

@@ -77,7 +77,7 @@
  * Serial port -1 is the USB emulated serial port, if available.
  * Note: The first serial port (-1 or 0) will always be used by the Arduino bootloader.
  *
- * :[-1, 0, 1, 2, 3, 4, 5, 6, 7]
+ * :[-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  */
 #define SERIAL_PORT 0
 
@@ -99,7 +99,7 @@
 /**
  * Select a secondary serial port on the board to use for communication with the host.
  * Currently Ethernet (-2) is only supported on Teensy 4.1 boards.
- * :[-2, -1, 0, 1, 2, 3, 4, 5, 6, 7]
+ * :[-2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  */
 //#define SERIAL_PORT_2 -1
 //#define BAUDRATE_2 250000   // :[2400, 9600, 19200, 38400, 57600, 115200, 250000, 500000, 1000000] Enable to override BAUDRATE
@@ -107,14 +107,14 @@
 /**
  * Select a third serial port on the board to use for communication with the host.
  * Currently only supported for AVR, DUE, LPC1768/9 and STM32/STM32F1
- * :[-1, 0, 1, 2, 3, 4, 5, 6, 7]
+ * :[-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  */
 //#define SERIAL_PORT_3 1
 //#define BAUDRATE_3 250000   // :[2400, 9600, 19200, 38400, 57600, 115200, 250000, 500000, 1000000] Enable to override BAUDRATE
 
 /**
  * Select a serial port to communicate with RS485 protocol
- * :[-1, 0, 1, 2, 3, 4, 5, 6, 7]
+ * :[-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  */
 //#define RS485_SERIAL_PORT 1
 #ifdef RS485_SERIAL_PORT

Marlin/src/HAL/STM32/MarlinSerial.cpp

@@ -37,6 +37,9 @@
 #ifndef USART5
   #define USART5 UART5
 #endif
+#ifndef USART6
+  #define USART6 UART6
+#endif
 #ifndef USART7
   #define USART7 UART7
 #endif