NUCLEO-H743ZI USB printf works in STM32CubeIDE but not in Keil

[LKris.1]

I have a problem with using the printf function in Keil. I used the STM32CubeMX to setup a project and generated the code for Keil.

All settings in CubeMX is standard, only thing changed is the USB_DEVICE set to Communication Device Class (Virtual Port Com).

If this is setup and genrate for STM32CubeIDE and then in main.c I add #include "stdio.h" and within User Code 4 I insert the following, then printf is working on the USB connection.

/* USER CODE BEGIN 4 */

int __io_putchar(int ch) {

uint8_t c[1];

c[0] = ch & 0x00FF;

HAL_UART_Transmit(&huart3, &*c, 1, 10);

return ch;

}

int _write(int file, char *ptr, int len) {

int DataIdx;

for (DataIdx = 0; DataIdx < len; DataIdx++) {

__io_putchar(*ptr++);

}

return len;

}

/* USER CODE END 4 */

If i then do the same thing for keil, its not working, anyone who can guide me how to solve this.

[Peter BENSCH · Accepted solution]

Compilers use different implementations for printf, GNU GCC calls e.g. __io_putchar, others call fputc

You could try:

#ifdef __GNUC__
  #define PUTCHAR_PROTOTYPE int __io_putchar(uint8_t ch)
#else
  #define PUTCHAR_PROTOTYPE int fputc(uint8_t 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 __io_putchar/fputc here, e.g.
  HAL_UART_Transmit(&huart2, &ch, 1, 3);
  return ch;
}

Good luck!

When your question is answered, please close this topic by choosing Select as Best. This will help other users find that answer faster.

/Peter

[Tesla DeLorean]

Keil doesn't use syscalls/write​

[LKris.1]

Hi Peter

I just tried this, actually i also tried this earliere, but its still not printing anything on my serial monitor.

Do you have an idea why its not working with my NUCLEO-H743ZI and Keil?