[LinuxPPS] precision

[Cirilo Bernardo]

> On problem could derive from IRQ latency... but in any case I don't
> see how we can improve it from LinuxPPS code.
>
> Other suggestions?

Sometimes a UART uses a 'soft interrupt' (very bad name for a timer).
In such a case, looking at the /proc entry should show IRQ 0 for that
UART. Timestamping from such a device will be characterized by large
jitter (at least larger than typical for a real interrupt). In such
a case it is also possible to miss assert/clear events.

IRQ latency on modern machines should be in the microsecond range, but
attaching a peripheral like a video framegrabber can really foul this
and push IRQ latency into the low millisecond range.

Can someone remind me what the precision issue is?

- Cirilo

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