Software timers using hardware interrupt

Question

I have to implement a counter for upto 30 minutes on my microcontroller. However the hardware interrupts maximum time is nowhere close to this. So I think I would be using the interrupt and increment a variable everytime the interrupt is called by the hardware. However I would like to know if there are already any such open source timers available which I can port and use more easily rather than writing evertything from scratch. The second question is :

interrupt timer()
{
/increment a count
} 

Other than setting a flag when my required counter value is reached is there any more efficient way of doing this?

Answer 1

Initialize a variable in the global scope, and then have your timer interrupt increment it and check the value. Its literally four lines of code.

• user43914: I agree. It was just that I wasnt sure if this was the way it is generally done since polling it from the main loop may not be very efficient.
• Passerby: @user43914 done all the time. The addition and comparison is very minimal codewise, only takes a few clock cycles.
• Connor Wolf: @user43914 - Don't forget to declare the variable volatile, so checks don't get compiled out.