Thanks JW. I can see you've used unsigned integers throughout and I think this is where I am getting confused as I would need the function to return a signed 64 bit result which could run positive and negative either side of zero.

I've been trying to develop a function to do what you suggest and read the TIM2 CNT register at a regular fast rate and extend its 32 bit value into 64 bits whilst coping with rollovers in both the up and down directions. The code I have so far is sh...

OK, thanks again. I'll do that.

Thanks for that. So amongst the registers associated with TIM2 are there flag bits which indicate a recent overflow or underflow condition?