STM32—printf function redefinition

　　In order to facilitate debugging, we often need to use the printf function to print out debugging information. In Keil software, if you want to use the printf output function, please note that you need to select the use MicrolLIB option first, as shown below.

　　Next, add the declaration of the printf function below the header file of the main function. The code is as follows:

/* Includes ------------------------------------------------------------------*/

#include "main.h"

#include "stm32f4xx_hal.h"

 // The added code is as follows, function refactoring

#ifdef __GNUC__ //gcc compiler macro definition

  /* 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__ */

/*The above means:

If the macro __GNUC__ is defined, that is, using the GCC compiler, then define the macro #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)

If the macro __GNUC__ is not defined, that is, the GCC compiler is not used, then define the macro #define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f) */

//Add the implementation part of printf reconstruction function

PUTCHAR_PROTOTYPE

{

    HAL_UART_Transmit(&huart1 , (uint8_t *)&ch, 1, 0xFFFF);

    return ch;

}

　　Add a print output function in the while(1) loop of the main function to test the effect.

  while (1)

    {

        printf("printf teset\r\n");//print output

        HAL_Delay(1000); //Delay 1S

    }

　　The test result is as shown in the figure below, which can realize the printing of printf function.