How to retarget printf() on an STM32F10x? - c

Question

I use this code for retarget printf(), but it does not work
#ifdef __GNUC__
/* With GCC/RAISONANCE, small printf (option LD Linker->Libraries->Small printf
set to 'Yes') calls __io_putchar() */
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
#define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif /* __GNUC__ */
PUTCHAR_PROTOTYPE
{
/* Place your implementation of fputc here */
/* e.g. write a character to the LCD */
lcd_Data_Write((u8)ch);
return ch;
}
I use STM32F103RBT6
compiler : GCC with emBitz editor

Answer 1

Try hijacking the _write function like so:
#define STDOUT_FILENO 1
#define STDERR_FILENO 2
int _write(int file, char *ptr, int len)
{
switch (file)
{
case STDOUT_FILENO: /*stdout*/
// Send the string somewhere
break;
case STDERR_FILENO: /* stderr */
// Send the string somewhere
break;
default:
return -1;
}
return len;
}

Answer 2

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 <stdio.h>
#include <stdarg.h>
#include <string.h>
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;
}
}
}

Answer 3

Tank you Bence Kaulics
I use tinyprintf library and it worked quite well : github link

Answer 4

just make sure to add the following in the init code:
// Turn off buffers, so I/O occurs immediately
setvbuf(stdin, NULL, _IONBF, 0);
setvbuf(stdout, NULL, _IONBF, 0);
setvbuf(stderr, NULL, _IONBF, 0);