Example semihosting code for Cortex-M4 stm32f429

semi.c

#include <stdint.h>

static int semihost_call(int service, void *opaque)
{
	register int r0 asm("r0") = service;
	register void *r1 asm("r1") = opaque;
	register int result asm("r0");
	asm volatile("bkpt 0xab"
	             : "=r" (result) : "r" (r0), "r" (r1));
	return result;
}

enum SEMIHOST_SVC {
	SYS_WRITEC = 0x03,
	SYS_WRITE0 = 0x04,
	SYS_WRITE  = 0x05,
};

void putchar(uint8_t chr)
{
	semihost_call(SYS_WRITEC, &chr);	
}

void puts(uint8_t *str)
{
    semihost_call(SYS_WRITE0, str)
}

void print(uint8_t msg[])
{
    uint32_t param[] = {1, (uint32_t) message, sizeof(message)};
    semihost_call(SYS_WRITE, (void *) param);
}