source: avrstuff/chiptest/main.c@ 6390cc3

#include <usart.h>

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>
#include <avr/pgmspace.h>
#include <util/delay.h>

#include <string.h>
#include <stdbool.h>

// muSerial: ATTiny2313 - LED = PD6
// K4KUSB: ATTiny2313 - LED = PB2
// STK500: anything, PORTD is convenient if available.
#define DDRLED DDRC
#define PORTLED PORTC
#define LEDBIT (1 << PC2)

int main() {
        wdt_enable(WDTO_2S);
    // configure timer 0 for a rate of FCPU/(256 * 256)
#ifdef __AVR_ATtiny2313__
    TCCR0A = 0;          // timer 0 prescaler: 256
        TCCR0B = 4;
#else
        TCCR0 = 6; // timer 0 prescaler: 256
#endif

        //debug LED - output
        DDRLED |= LEDBIT;
        PORTLED &= ~LEDBIT;

        USARTInit();

        // Let's rock!
        uint8_t counter = 0;
        char c = 'a';
        for(;;) {
                wdt_reset();

                // Wait for timer overflow...
                if (TIFR & (1 << TOV0)) {
                        TIFR = (1 << TOV0); // reset flag
                        counter++;

                        if (counter == 0)
                        {
                                PORTLED ^= LEDBIT; // Toggle the LED
                                USARTWriteChar(c++); // Send a byte to the UART
                                if (c > 'z')
                                        c = 'a';
                        }
                }
        }

        return 0;
}