I have severe problems with time distance measurement. In the timer2 ISR I count the number of overflow and the number of external events. After a given limit of samples is reached, I get the captured value. From time to time and at certain frequencys I am loosing exactly 1 overflow.

Real example:

Processor = 22 MHz
Input = 3Khz
Samples to take = 128
Counted overflows = 1
Captured counts = 49766
total counts = 115,302 = 3 KHz
ISR takes about = 40us

I took into consideration, that both events - overflow and capture - might take place at the same ISR cycle in a asynchronous way. I change the ISR to reject such a situation. But nothing changed. I would be glad to get any help.
Regards Udo Barthel