AVR Freaks

I don't know where you get your values in your code from, but here is what I get from the CV wizard:

// Timer/Counter 1 initialization
// Clock source: System Clock
// Clock value: 31.250 kHz
// Mode: CTC top=OCR1A
// OC1A output: Toggle on compare match
// OC1B output: Disconnected
// Noise Canceler: Off
// Input Capture on Falling Edge
// Timer Period: 1 s
// Output Pulse(s):
// OC1A Period: 2 s Width: 1 s
// Timer1 Overflow Interrupt: Off
// Input Capture Interrupt: Off
// Compare A Match Interrupt: On
// Compare B Match Interrupt: Off
TCCR1A=(0<<COM1A1) | (1<<COM1A0) | (0<<COM1B1) | (0<<COM1B0) | (0<<WGM11) | (0<<WGM10);
TCCR1B=(0<<ICNC1) | (0<<ICES1) | (0<<WGM13) | (1<<WGM12) | (1<<CS12) | (0<<CS11) | (0<<CS10);
TCNT1H=0x0B;
TCNT1L=0xDC;
ICR1H=0x00;
ICR1L=0x00;
OCR1AH=0x7A;
OCR1AL=0x11;
OCR1BH=0x00;
OCR1BL=0x00;

// Timer/Counter 1 Interrupt(s) initialization
TIMSK1=(0<<ICIE1) | (0<<OCIE1B) | (1<<OCIE1A) | (0<<TOIE1);

My code uses the OCRA output to toggle so you would only have to reload the base count in the ISR.

Untested, but eh Wizard is pretty good/excellent.

Jim

int main(void)
{
    sei();

sei() is soemthing you only do when you have everything else "ready to go". So you set up all your interrupt sources and configure your peripherals and then you SEI. It's not your problem at the moment but as you have it you start to set timer registers while I is active. Luckily you left the setting of the OCIE bit to the last action.

BTW as it is a 168 did you know that instead of:

ISR(TIMER1_COMPA_vect)                    //Interrupt service routine
{
	PORTC ^= (1 << 0);                    //Toggle led
}

you could use:

ISR(TIMER1_COMPA_vect)                    //Interrupt service routine
{
	PINC = (1 << 0);                    //Toggle led
}

because the 168 was one of the first AVRs to support the "toggle on PIN write" feature?

Anyway I put your code in the simulator and it hit a breakpoint in the ISR after 3,999,786 cycles so that would be about 4 seconds if the 168 was running at the default 1MHz. To complete a whole "flash cycle" the LED would be on for 4s and off for 4s so it would have an 8s period (0.125Hz).

(running 4 million cycles in the AS7 simulator takes a LONG(!) time)

So it must have been a hardware issue because today I did not change any code,

Now you allow yourself to fall into the software flytrap, where you will be crushed and eaten.  So in a few months all of your washing machines, electronic locks, or whatever uses this code will need recalled due to a mysterious "problem".

How do you know you don't have a random initialization problem or improper condition of some sort. Always check for such things before quickly dismissing a sign of something wrong.  Being quickly dismissive is the flytrap's secret weapon.