#define baud 9600
#define serial_bit_delay 1000000/baud
#define SERIAL_LOW() PORTB &= ~_BV(PB4)
#define SERIAL_HIGH() PORTB |= _BV(PB4)

// write out a byte as software emulated Uart
void serial_putchar(uint8_t byte)
{
    uint8_t mask;
    SERIAL_LOW(); // signal start bit
    _delay_us(serial_bit_delay);
    for (mask = 0x01; mask; mask <<= 1) {
        if (byte & mask) { // choose bit
            SERIAL_HIGH(); // send 1
        } else {
            SERIAL_LOW(); // send 0
        }
        _delay_us(serial_bit_delay);
    }
    SERIAL_HIGH();  //signal end bit
    _delay_us(serial_bit_delay);
}

void serial_puts(const char* str)
{
    while (*str) {
        serial_putchar((uint8_t)*str);
        ++str;
    }
    serial_putchar('\r');
    serial_putchar('\n');
}