How to retarget printf() on an STM32F10x?

Question

I use this code for retarget printf(), but it does not work

#ifdef __GNUC__
/* With GCC/RAISONANCE, small printf (option LD Linker->Libraries->         


        

Answer 1

As an alternative, you could write your own printf() function using, Variable Argument Functions (va_list).

With va_list a custom print function looks like the following:

#include 
#include 
#include 

void vprint(const char *fmt, va_list argp)
{
    char string[200];
    if(0 < vsprintf(string,fmt,argp)) // build string
    {
        HAL_UART_Transmit(&huart1, (uint8_t*)string, strlen(string), 0xffffff); // send message via UART
    }
}

void my_printf(const char *fmt, ...) // custom printf() function
{
    va_list argp;
    va_start(argp, fmt);
    vprint(target, fmt, argp);
    va_end(argp);
}

Usage example:

uint16_t year = 2016;
uint8_t month = 10;
uint8_t day   = 02;
char* date = "date";

// "Today's date: 2015-12-18"
my_printf("Today's %s: %d-%d-%d\r\n", date, year, month, day);

Note that while this solution gives you convenient function to use, it is slower than sending raw data or using even sprintf(). I have used this solution both on AVR and on STM32 microcontrollers.

You could further modify the vprint like this, where periphery_t is a simple enum type:

void vprint(periphery_t target, const char *fmt, va_list argp)
{
    char string[200];
    if(0 < vsprintf(string,fmt,argp))
    {
        switch(target)
        {
            case PC: PC_send_str(string);
                break;
            case GSM: GSM_send_str(string);
                break;
            case LCD: LCD_print_str(string);
                break;
            default: LCD_print_str(string);
                break;
        }
    }
}