Are you asking whether or not function A can be interrupted by an interrupt and, within that interrupt, you can call function A?

If so, that depends on whether your compiler allows re-entrant code. If it does, you can. If it doesn't, you can't. This also may be a compiler switch.

If you are working in assembly it depends on how you handle your registers and stack within the function in question.

Personally, I try to do as little as possible in an interrupt. Rather, try having the interrupt save the information you need and then process it later--outside of the interrupt.

Craig Steiner