feat: add STM32 four-channel weighing firmware

STM32_4路称重_Git提交精简工程/gcc_build/gcc_syscalls.c

@@ -0,0 +1,17 @@
+#include "stm32f10x.h"
+
+int _write(int file, char *data, int length)
+{
+    int index;
+
+    (void)file;
+    for (index = 0; index < length; ++index)
+    {
+        while (USART_GetFlagStatus(UART5, USART_FLAG_TC) == RESET)
+        {
+        }
+        USART_SendData(UART5, (uint8_t)data[index]);
+    }
+
+    return length;
+}