use standard C library and printf redirection to USART/ITM for debugging need disable semihosting mode on Keil MDK ARM

disablesemihost.c

/*
 * add the below code snippt into your project
 */
#include <stdio.h>

#pragma import(__use_no_semihosting)

struct __FILE
{
    int handle;
};

FILE __stdout;
/**
 * @brief define _sys_exit() to avoid using semihosting mode
 * @param void
 * @return  void
 */
void _sys_exit(int x)
{
    x = x;
}