On Tue Aug 25 2020, Vladimir Oltean wrote: > On Tue, Aug 25, 2020 at 11:33:53AM +0200, Kurt Kanzenbach wrote: >> On Tue Aug 25 2020, Vladimir Oltean wrote: >> > On Thu, Aug 20, 2020 at 10:11:15AM +0200, Kurt Kanzenbach wrote: >> > >> > Explain again how this works, please? The hrtimer measures the CLOCK_TAI >> > of the CPU, but you are offloading the CLOCK_TAI domain of the NIC? So >> > you are assuming that the CPU and the NIC PHC are synchronized? What if >> > they aren't? >> >> Yes, I assume that's synchronized with e.g. phc2sys. >> > > My intuition tells me that this isn't the user's expectation, and that > it should do the right thing even if it's not synchronized to the system > clock. I get your point. But how to do it? We would need a timer based on the PTP clock in the switch. > >> > >> > And what if the base-time is in the past, do you deal with that (how >> > does the hardware deal with a base-time in the past)? >> > A base-time in the past (example: 0) should work: you should advance the >> > base-time into the nearest future multiple of the cycle-time, to at >> > least preserve phase correctness of the schedule. >> >> If the hrtimer is programmed with a value in the past, it fires >> instantly. > > Yes, it does. > >> The callback is executed and the start time is programmed. >> > > With a valid value from the hardware's perspective? Yes. That's no problem. Thanks, Kurt
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