AVR Freaks

http://www.nongnu.org/avr-libc/u...

So a minimal AVR program to use something like printf() might be:

#define F_CPU 16000000UL
#define BAUD 9600
#include <stdio.h>
#include <avr/io.h>
#include <util/setbaud.h> // uses BAUD and F_CPU as input, outputs UBRR_VALUE

void uart_init(void) {
	UBRR = UBRR_VALUE;
	UCSRB = (1 << TXEN);
}

int	uart_putchar(char c, FILE *stream) {
	loop_until_bit_is_set(UCSRA, UDRE);
	UDR = c;

	return 0;
}

FILE uart_str = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);

int main(void) {
        uart_init();
	stdout =  &uart_str;

	while(1) {
		printf("Hello world\n");
	}
}

The only "trick" in any of that is the FDEV_SETUP_STREAM and the connection to stdout. But as soon as you have made a connection between stdout and a uart_putchar() routine then all the usual stdio.h output routines are connected and ready to use.

The reason it's done like this is that the output could just as easily have been an LCD with LCD_init() and an LCD_putchar() instead. It's up to you what output device you'd like to use.

The same technology also allows for a uart_getchar() and then connecting that to stdin after which all the things like scanf() could be used too.