Time Card and PTP on a Raspberry Pi Compute Module 4

Re:Time Card and PTP on a Raspberry Pi Compute Module 4 by bestouff on Friday September 03, 2021 @09:25AM (#28403877)

PTP and NTP don't have the same use:

- PTP is for sub-nanosecond local networks, with possibly hundreds of packets per second, local (in network card) clocks, hardware timestamping everywhere

- NTP if for long distance sync, with sophisticated statistical smoothing from several upstream servers

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Re:Time Card and PTP on a Raspberry Pi Compute Module 4 by jhellan on Friday September 03, 2021 @09:33AM (#28403975)

Basically, PTP assumes that network delays are deterministic. If that's true, it is very precise. If not, PTP is the wrong tool. NTP assumes that network delays are stochastic, and uses sophisticated algorithms to account for this. PTP has much simpler algorithms, which can be implemented in electronics, where internal timings can be characterized. NTP is more complex, and tends to run on a general purpose computer. This adds internal OS timings to the uncertainty.

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