Messages in this thread | | | Date | Wed, 5 Jun 2019 20:11:35 -0700 | From | Richard Cochran <> | Subject | Re: [PATCH v3 net-next 00/17] PTP support for the SJA1105 DSA driver |
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On Wed, Jun 05, 2019 at 09:08:54PM +0300, Vladimir Oltean wrote: > Currently I'm using a cyclecounter, but I *will* need actual PHC > manipulations for the time-based shaping and policing features that > the switch has in hardware.
Okay.
> On the other hand I get much tighter sync > offset using the free-running counter than with hardware-corrected > timestamps.
Why? The time stamps come from the very same counter, don't they?
> So as far as I see it, I'll need to have two sets of > operations.
I doubt very much that this will work well.
> How should I design such a dual-PHC device driver? Just register two > separate clocks, one for the timestamping counter, the other for the > scheduling/policing PTP clock, and have phc2sys keep them in sync > externally to the driver?
But how would phc2sys do this? By comparing clock_gettime() values? That would surely introduce unnecessary time error.
> Or implement the hardware corrections > alongside the timecounter ones, and expose a single PHC (and for > clock_gettime, just pick one of the time sources)?
I would implement the hardware clock and drop the timecounter altogether.
HTH, Richard
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