Timer interrupt routine called immediately all the time.

Hello.

I am not sure if this is the right place. Let me know and I will remove it.

I am using Atmel Studio 7 and I create a new project from an Arduino sketch.

I then program any of the 16 bit timers to trigger a timer overflow interrupt every second.
Please have in mind that the sketch I am compiling, includes some libraries that make use of the millis() function.

What I see, no matter which of the 16 bit timers I use, is that it overflows without any delay.
Even if I program the 1024 prescaler, no matter what, it will enter the interrupt routine immediately.

Any ideas?

Thanks.

Any code to see?

Unfortunately not now, but it really doesn't have any errors. I was trying for at least a couple of hours yesterday. I think it has something to do with the arduino way of using some other timers (? perhaps?).

I will paste some code later today.

I found the problem.

The init function, called prior to setup, inside main, initializes almost all timer registers.
I was unaware of that, so I was only programming the features I wanted, for example, I needed only the time overflow interrupt, so I was leaving OCCR registers as they were.

Do you know if there are other issues to consider, where arduino handles things automatically and I shouldn't use?

Thanks,
Bill.

In the init() function is all stuff initialized at start, before setup() function.