On 21/06/2022 01:31, chris wrote:
Sorry David, but that is incorrect. If you look at the app note you
posted, input capture section, quite clearly states that:
> When the rising or falling edge is detected at the CCP1 pin,
> the interrupt flag CCP1IF bit is set.
If you go to a more primary source
<https://ww1.microchip.com/downloads/en/DeviceDoc/60001122G.pdf>, you
will see, in the diagram on page 15-3, that the logic path for raising
interrupts diverges from that for doing the capture, after the event
detection, so the capture is not dependent on the interrupt occurring.
Also, on page 15-4, that the actual interrupt can be selectively disabled.
In my original response, I did meant to add that there would typically
be an interrupt, but that the interrupt could be handled with low
priority (you will get a good result any time until the timer actually
wraps round. Even then, the use of an interrupt is not a fundamental
requirement.
For a dedicated appliance, interrupts can actually be a liability, as
they can introduce race conditions. Nonetheless, I think all current
microcontrollers support them.
With precision time, over Ethernet, one would expect the normal Ethernet
device driver interrupt handling, but, for example, the device driver
might well service several incoming messages on one interrupt. However
capturing the event time still means that nano-second accuracy is possible.
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