add support for cstx stm32f103re dtu board

board/CSTX_STM32F103RE_DTU/BSP/Src/main.c

@@ -0,0 +1,23 @@
+#include "mcu_init.h"
+#include "cmsis_os.h"
+
+#define APPLICATION_TASK_STK_SIZE       1024
+extern void application_entry(void *arg);
+osThreadDef(application_entry, osPriorityNormal, 1, APPLICATION_TASK_STK_SIZE);
+
+__weak void application_entry(void *arg)
+{
+    while (1) {
+        printf("This is a demo task,please use your task entry!\r\n");
+        tos_task_delay(1000);
+    }
+}
+
+int main(void)
+{
+    board_init();
+    printf("Welcome to TencentOS tiny\r\n");
+    osKernelInitialize();
+    osThreadCreate(osThread(application_entry), NULL);
+    osKernelStart();
+}