stm32 c, export prototype to rest of project

Question

I'm developing a little project (c) in stm32f407vg and following the UART tutorial in:

http://letanphuc.net/2015/09/stm32f0-uart-tutorial-5/#comment-346

My problem is with the function prototype:

/* Includes ——————————————————————*/
#include “usart.h”
#include “gpio.h”

/* Private function prototypes ———————————————–*/
#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__ */

/**
* @brief Retargets the C library printf function to the USART.
* @param None
* @retval None
*/
PUTCHAR_PROTOTYPE
{
/* Place your implementation of fputc here */
/* e.g. write a character to the USART */
HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, 100);
return ch;
}
/* USER CODE END PFP */

UART_HandleTypeDef huart1;

/* USART1 init function */

void MX_USART1_UART_Init(void)
{
…
..
..

How I have to do the declaration in usart.h so I can use printf() the rest of the project?

Thanks.

EDIT: 2017/01/20 response to Guillaume Michel

I've put in usart.h

#ifndef __usart_H
#define __usart_H

/* Includes ------------------------------------------------------------------*/
#include "stm32f4xx_hal.h"
#include "globals.h"

extern UART_HandleTypeDef huart1;

/* **********************************************
 *
 * **********************************************/
#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__ */

and the PUTCHAR_PROTOTYPE at usart.c:

/* Includes ------------------------------------------------------------------*/
#include "usart.h"
#include "gpio.h"

#include "string.h"


PUTCHAR_PROTOTYPE
{
    /* Place your implementation of fputc here */
    /* e.g. write a character to the USART */
    HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, 100);
    return ch;
}
/* USER CODE END PFP */

//UART_HandleTypeDef huart1;

/* USART1 init function */

void MX_USART1_UART_Init(void){
..
..
}

And in main.c:

/* Includes ------------------------------------------------------------------*/
#include "globals.h"
#include "stm32f4xx_hal.h"
#include "syscfg.h"
#include "can.h"
#include "usart.h"
#include "gpio.h"

#include "kernel.h"

#include <stdio.h>

int main(void){
    SysIniCfg();
    printf("Hola");
    while (1){

        //kernelMotor();

        HAL_GPIO_TogglePin(LED_G_GPIO_Port,LED_G_Pin);

    }
}

I have tried other places to put the two sections of the code but this is the only one I don't get warnings or errors

Answer 1

I am pretty sure there is a catch, otherwise you wouldn't ask the question, but I think that if you cut and paste the code below in your uart.h, that should 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__ */

Don't forget to include uart.h everywhere you call printf

Answer 2

if you are using Newlib libc in your project (STM32Cube generated) you just need to implement int __io_putchar(int ch) any where in the project (main.c if you like), this implementation is used for to outputting characters to the standard output (by printf).

notice that extern int __io_putchar(int ch) __attribute__((weak)); is weakly linked in syscalls.c.

during compilation only the prototype of the function is used, and during the linking of the project, the user defined function is used.

including uart.h all over your project is not a neat solution. make sure you have the rest of Newlib files included.