timeout.c

volatile bool tx_sumd = false;
volatile bool timedout = false;

// Set tx_sumd = true every 10ms
void initSUMDTimer() {
    cli();
    TCCR1A = 0;
    TCCR1B = 0;
    TCNT1  = 0;

    OCR1A = 2500;                         // compare match register 16MHz/64/10Hz
    TCCR1B |= (1 << WGM12);               // CTC mode
    TCCR1B |= (1 << CS11) | (1 << CS10);  // 64 prescaler
    TIMSK1 |= (1 << OCIE1A);              // enable timer compare interrupt
    sei();
}

#define T2_9MS (255-141)
#define T2_10MS (255-156)

// Set timeout = true every 9ms (unless we got a packet)
void initTimeoutTimer() {
    cli();
    TCCR2A = 0;
    TCCR2B = 0;
    TCNT2  = T2_9MS; // about 9ms to go

    TCCR2B |= (1 << CS22) | (1 << CS21)  | (1 << CS20);  // 1024 prescaler
    TIMSK2 |= (1 << TOIE2);              // enable timer overflow interrupt
    sei();
}

ISR(TIMER1_COMPA_vect) {
    tx_sumd = true;
}

ISR(TIMER2_OVF_vect) {
    timedout = true;
}