Timer interrupts and Atomic macros

Projects Programming
1

I've written a sketch that usesTimer1 to create periodic CTC interrupts. I have an ISR(TIMER1_COMPA_vect) interrupt service routine that is called on each interrupt. It's all working well.

However, I have a couple uint32_t (unsigned long) variables shared between the ISR and the main loop. So I should probably protect access to these variables with the ATOMIC_BLOCK macro from the avr lib's util/atomic.h. But here is a concern. These macros work by using the cli() and sei() functions to clear and set the global interrupt flag during the protected block. If the next timer interrupt happens to come while in the middle of one of these blocks, will the interrupt be lost, or will it be deferred, held in a pending state, and fire as seen as the protected block ends and the global interrupt flag is turned on again?

2

It will be held.
Just get finished with the section of code as fast as you can.
Some great reading here:

3

Thanks. That's an excellent article, too. My Atomic block will only be long enough to copy the shared variable to a non-shared one.

4

You will be ok then.

5

My Atomic block will only be long enough to copy the shared variable to a non-shared one.

In loop() (or some other function), right? Not in the interrupt service routine, right?

In the ISR, interrupts are disabled, so atomic block operations are not needed.