Retargeting printf on STM32F746G

[Renaud Dk]

Hi,

I'm using STM32CubeIDE and I'm trying to retarget printf to the USART1 of the STM32F746G.

USART1 of the MCU is connected to the ST-Link Virtual com. I have tested the connection the USART1 directly using the function "HAL_UART_Transmit(&huart1, "A", 1, 0xFFFF)" this does work meaning that the hardware is correctly setup. So far I have implemented __io_putchar() function in my main.cpp like the following :

int __io_putchar(int ch)

{

 /* Place your implementation of fputc here */

 /* e.g. write a character to the EVAL_COM1 and Loop until the end of transmission */

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

 return ch;

}

I took the code from the one of the example in the STM32Cube_FW_F7_V1.15.0 but for an other board since there is no UART_printf example for the STM32F746G.

Any of what could be wrong with my implementation ?

[Olivier GALLIEN]

Hi @Renaud Dk​ 

Does your project embed syscall.c ?

Else customized _write function has to be defined also.

Please refer to "AN4989 STM32 microcontroller debug toolbox" Chapter 7.

https://www.st.com/content/ccc/resource/technical/document/application_note/group0/3d/a5/0e/30/76/51/45/58/DM00354244/files/DM00354244.pdf/jcr:content/translations/en.DM00354244.pdf

Olivier

[Renaud Dk]

Hi @Community member​ 

Yes I have syscall.c integrated in my project (under [PROJECT_ROOT]/Core/Src). I read the app note and this why I chose to implement the __io_putchar() instead of _write(). One word about my project configuration, my main.cpp is in C++ because I'm using touchgfx framework with CMSIS-Freertos.

Renaud

[Pavel A.]

> Any of what could be wrong with my implementation ?

Try two small changes before digging deeper:

1: in your __io_putchar:

extern "C"
int __io_putchar(int ch)
{
    if (ch == '\n')
        HAL_UART_Transmit(&huart1, (uint8_t *)"\r", 1, 0xFFFF);
    HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, 0xFFFF);
    return ch;
}

2: in UART1 advanced settings (in CubeMX) - make sure to disable overrun detection.

-- pa