CODEWITHSUNDEEP
cembeddedprintfstdoutstm32
Mouin
Mouin

Reputation: 1103

Retarget printf to a serial port

I want use the function printf to print character on the serial port. I have read these 2 posts 1 and 2, But I'am not sure to understand the manip:

in the 1st link it's said:

To enable printf functionality, first you need to create a new __FILE struct. This struct is then called with FILE struct.

Why I have to create __FILE struct I didn't realy undrestand this sentence.

In the 2nd link it's said

To complete the separation from the standard I/O library we also have had to redefine __stdout and __stdin. These can be found inside the retarget.c file below the declaration of the __FILE structure.

If I redefine these 2 variables isn't that a compilation error I mean a redefinition.

Upvotes: 0

Views: 7521

Answers (2)

Farrukh
Farrukh

Reputation: 61

Add this piece of code in your code

#ifdef __GNUC__
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
#define PUTCHAR_PROTOTYPE int fputc(int ch, FILE * f)
#endif

PUTCHAR_PROTOTYPE {
    HAL_UART_Transmit( & huart2, (uint8_t * ) & ch, 1, 0xFFFF);
    return ch;
}

Only thing to edit is this line, set it as per your device serial port driver

HAL_UART_Transmit( & huart2, (uint8_t * ) & ch, 1, 0xFFFF);

Upvotes: 0

SamR
SamR

Reputation: 399

This may possibly a duplication of How to make printf work on STM32F103?

I will put my answer, which I posted in the above thread, here too, anyway.

Writing an own printf implementation is an option, and probably the most recommended option according to me. Get some inspiration from the standard library implementation and write your own version, only to cater your requirements. In general, what you have to do is, first retarget a putc function to send char s through your serial interface. Then override the printf method by using the putc custom implementation. Perhaps, a very simple approach is sending the string character-wise by recursive calls for putc function.

Last but not least, you can find some lightweight printf implementations. The code size and the set of features offered by these lightweight implementations lie in between the custom written printf function and the stock standard prinf function (aka the beast). I have recently tried this and very pleased with its performance on an ARM core in terms of memory footprint and the number of execution cycles required. http://www.sparetimelabs.com/tinyprintf/tinyprintf.php

-PS

Copied from my own writings sometime back - http://mycola.info/2015/02/09/lightweight-printfscanf-for-embedded-applications/

Upvotes: 1

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