I am working on an RC meter. The measurement requires four digit precision of time measurement. I have tried using nanosleep,pigpio, direct gpio interrupt routin, but I could reach only three stable digits.
Direct interrupt programming called my attention to FIQ which may solve the problem. What plan to do:
Insert a code between FIQ and the current FIQ routin (USB). FIQ also activated by gpio edge, read a free running timer for timestemp, if not my GPIO edge activated FIQ call original one, do calculations in a userland program.
Any suggestion, advice or example program how to program FIQ highly appriciated!