On 23.04.2013, at 3:02, Jim Lux wrote: > > Assuming the software is reading some hardware counter when it gets the > pulse, there could be variable latency in the routine. 8000 ticks is a lot > of instructions though..
The hw timer latches the counter value to a separate register when the leading edge of PPS arrives, and raises an interrupt. The ISR simply reads the latched value and subtracts the previous value to get the duration. So interrupt latency shouldn't be an issue. > > If you read, say, 100 intervals, what does the distribution look like? > is it always the same number (crystal is too high in frequency), or does it > vary (software might be an issue) These are 100 intervals, you can see them going steadily up and then down, and up again. A sawtooth of gigantic proportions. 84007993 84008000 84008001 84008004 84008005 84008007 84008010 84008012 84008014 84008017 84008018 84008021 84008025 84008026 84008030 84008031 84008036 84008037 84008038 84008042 84008045 84008046 84008049 84008051 84008053 84008054 84008058 84008059 84008061 84008064 84008067 84008069 84008071 84008038 84007998 84008001 84008005 84008005 84008009 84008010 84008013 84008015 84008018 84008018 84008023 84008024 84008025 84008029 84008032 84008034 84008036 84008037 84008043 84008044 84008046 84008048 84008051 84008054 84008056 84008058 84008059 84008061 84008064 84008068 84008069 84008067 84007993 84008000 84008001 84008004 84008008 84008009 84008012 84008014 84008016 84008019 84008021 84008022 84008025 84008026 84008030 84008030 84008035 84008036 84008039 84008041 84008045 84008046 84008048 84008051 84008054 84008055 84008058 84008060 84008062 84008062 84008067 84008068 84008068 84007993 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
