[quote user="Mark LoBuono"]Most of the time my values are +8/-8 counts, interrupt to interrupt, which is what I expect. Periodically, my values are off by hundreds of counts and I cannot figure out why! [/quote]Rather than using an input interrupt to trigger a timer read in software, could you use a timer in Input Edge-Time Mode to cause the timer to capture the time of an input edge on a Capture/Compare/PWM pin? If the timer hardware performs the capture of the input edge, I think the count variation due to software interrupt latency should be avoided. [My suggestion is based on a quick read of the TM4C123GH6PM datasheet, I haven't attempted to implement Input Edge-Time Mode]
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