M252: Support configurability of USB/STDIO UART pins

-   STDIO_UART and STDIO_UART_TX/STDIO_UART_RX
-   USB_UART and USBTX/USBRX

targets/TARGET_NUVOTON/TARGET_M251/PeripheralNames.h

@@ -20,6 +20,7 @@
 #define MBED_PERIPHERALNAMES_H
 
 #include "cmsis.h"
+#include "PinNames.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -77,7 +78,16 @@ typedef enum {
     UART_2 = (int) NU_MODNAME(UART2_BASE, 2, 0),
 
     /* NOTE: board-specific */
-    STDIO_UART  = UART_0
+#if defined(MBED_CONF_TARGET_USB_UART)
+    USB_UART    = MBED_CONF_TARGET_USB_UART,
+#else
+    USB_UART    = NC,
+#endif
+#if defined(MBED_CONF_TARGET_STDIO_UART)
+    STDIO_UART  = MBED_CONF_TARGET_STDIO_UART
+#else
+    STDIO_UART  = USB_UART
+#endif
 } UARTName;
 
 typedef enum {

targets/TARGET_NUVOTON/TARGET_M251/PinNames.h

@@ -107,10 +107,26 @@ typedef enum {
     /* Other board-specific naming */
 
     /* UART naming */
-    USBTX = PB_13,
+#if defined(MBED_CONF_TARGET_USB_UART_TX)
-    USBRX = PB_12,
+    USBTX           = MBED_CONF_TARGET_USB_UART_TX,
+#else
+    USBTX           = NC,
+#endif
+#if defined(MBED_CONF_TARGET_USB_UART_RX)
+    USBRX           = MBED_CONF_TARGET_USB_UART_RX,
+#else
+    USBRX           = NC,
+#endif
+#if defined(MBED_CONF_TARGET_STDIO_UART_TX)
+    STDIO_UART_TX   = MBED_CONF_TARGET_STDIO_UART_TX,
+#else
     STDIO_UART_TX   = USBTX,
+#endif
+#if defined(MBED_CONF_TARGET_STDIO_UART_RX)
+    STDIO_UART_RX   = MBED_CONF_TARGET_STDIO_UART_RX,
+#else
     STDIO_UART_RX   = USBRX,
+#endif
     SERIAL_TX       = D10,
     SERIAL_RX       = D13,
 

targets/targets.json

@@ -5656,6 +5656,30 @@
             "IAR"
         ],
         "config": {
+            "usb-uart": {
+                "help": "Configure USB_UART. USB_UART and USB_UART_TX/USB_UART_RX must be consistent.",
+                "value": null
+            },
+            "usb-uart-tx": {
+                "help": "Configure USBTX. USB_UART and USBTX/USBRX must be consistent.",
+                "value": null
+            },
+            "usb-uart-rx": {
+                "help": "Configure USBRX. USB_UART and USBTX/USBRX must be consistent.",
+                "value": null
+            },
+            "stdio-uart": {
+                "help": "Configure STDIO_UART. STDIO_UART and STDIO_UART_TX/STDIO_UART_RX must be consistent. STDIO_UART defaults to USB_UART.",
+                "value": null
+            },
+            "stdio-uart-tx": {
+                "help": "Configure STDIO_UART_TX. STDIO_UART and STDIO_UART_TX/STDIO_UART_RX must be consistent. STDIO_UART_TX defaults to USBTX.",
+                "value": null
+            },
+            "stdio-uart-rx": {
+                "help": "Configure STDIO_UART_RX. STDIO_UART and STDIO_UART_TX/STDIO_UART_RX must be consistent. STDIO_UART_RX defaults to USBRX.",
+                "value": null
+            },
             "gpio-irq-debounce-enable": {
                 "help": "Enable GPIO IRQ debounce",
                 "value": 0
@@ -5733,7 +5757,12 @@
             "2",
             "5"
         ],
-        "device_name": "M252KG6AE"
+        "device_name": "M252KG6AE",
+        "overrides": {
+            "usb-uart": "UART_0",
+            "usb-uart-tx": "PB_13",
+            "usb-uart-rx": "PB_12"
+        }
     },
     "TMPM4G9": {
         "inherits": [