add support for GD32F310G-START

board/GD32F310G_START/BSP/Src/mcu_init.c

@@ -0,0 +1,36 @@
+#include "mcu_init.h"
+
+#define USART_CONSOLE (USART0)
+int fputc(int ch, FILE *f)
+{
+  if (ch == '\n') {
+    while(RESET == usart_flag_get(USART_CONSOLE, USART_FLAG_TBE));
+    /* Auto complete return char */
+    usart_data_transmit(USART_CONSOLE, '\r');
+  }
+  while(RESET == usart_flag_get(USART_CONSOLE, USART_FLAG_TBE));
+  usart_data_transmit(USART_CONSOLE, ch);
+  return ch;
+}
+
+int _write(int fd, char *ptr, int len)
+{
+    int i = 0;
+    for (; i < len; i++)
+    {
+        if (*(ptr + i) == '\n') {
+          while(RESET == usart_flag_get(USART_CONSOLE, USART_FLAG_TBE));
+          /* Auto complete return char */
+          usart_data_transmit(USART_CONSOLE, '\r');
+        }
+        while(RESET == usart_flag_get(USART_CONSOLE, USART_FLAG_TBE));
+        usart_data_transmit(USART_CONSOLE, *(ptr + i));
+    }
+    return len;
+}
+
+void board_init(void)
+{
+    board_gpio_init();
+    board_usart_init();
+}