testvariant1-avr-atmega328p.c

#define F_CPU 16000000UL
#define BAUD 9600

#include <util/setbaud.h>
#include <avr/io.h>
#include <stdio.h>

void uart_init(void) {
	UBRR0H = UBRRH_VALUE;
	UBRR0L = UBRRL_VALUE;

	#if USE_2X
	UCSR0A |= _BV(U2X0);
	#else
	UCSR0A &= ~(_BV(U2X0));
	#endif

	UCSR0C = _BV(UCSZ01) | _BV(UCSZ00); /* 8-bit data */
	UCSR0B = _BV(RXEN0) | _BV(TXEN0);   /* Enable RX and TX */
}

void uart_putchar(char c, FILE *stream) {
	if (c == '\n') {
		uart_putchar('\r', stream);
	}
	loop_until_bit_is_set(UCSR0A, UDRE0);
	UDR0 = c;
}

char uart_getchar(FILE *stream) {
	loop_until_bit_is_set(UCSR0A, RXC0); /* Wait until data exists. */
	return UDR0;
}

FILE uart_output = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);
FILE uart_input = FDEV_SETUP_STREAM(NULL, uart_getchar, _FDEV_SETUP_READ);
FILE uart_io = FDEV_SETUP_STREAM(uart_putchar, uart_getchar, _FDEV_SETUP_RW);

int main(void)
{
	char buffer[128] = "HELLO WORLD\n";
	char secret[128] = "SECRET DATA DO NOT PRINT\n";
	uart_init();
	stdout = &uart_output;
	stdin  = &uart_input;
    printf(buffer);
    while (1) 
    {
		printf(buffer);
    }
}