Redirect printf() to COM port

Why not build your own printf_usb function not to rely on specifics? This way you can even customize the escape codes... Got custon printf for text lcd, serial, usb, modem etc... One printf won t be enough over time.

My experience with "newlib-nano" is that what you really want to do is to provide "_write_r()" and/or "write()" following the defined interfaces.

/* Get newlib's definition of "reent" */
#include <reent.h>
#include "main.h"
 
/* newlib nano provides a stub version of "_write_r()" that does nothing. The stub has a
 * weak binding, so defining the function in your own files will override the stub.
 */
_ssize_t _write_r(struct _reent *ptr, /* Don't worry about what's in this for the simple case */
 int fd, /* ignored */
 const void* buf, /* the data to be sent out the UART */
 size_t cnt) /* the number of bytes to be sent */
{
 /* Replace "huart3" with the pointer to the UART or USART instance you are using
 * in your project
 */
 HAL_UART_Transmit(&huart3, (uint8_t*)buf, cnt, 1000);
 
 return (_ssize_t)cnt;
}

This version does not handle inserting a "\r" before "\n"; that would be better done in "write()" for the general case, but I leave that up to you if you want it.

Thanks, that works fine.

int _write(int fd, const void *buf, size_t count);

You can use this simpler version and not include reent.h.