Hi Kamil, On Thu, Oct 08, 2020 at 02:55:57PM +0200, Kamil Alkhouri wrote: > Hello dears, > > On Thu, 2020-10-08 at 12:01 +0200, Kurt Kanzenbach wrote: > > On Thu Oct 08 2020, Vladimir Oltean wrote: > > > On Thu, Oct 08, 2020 at 10:34:11AM +0200, Kurt Kanzenbach wrote: > > > > On Wed Oct 07 2020, Vladimir Oltean wrote: > > > > > On Wed, Oct 07, 2020 at 12:39:49PM +0200, Kurt Kanzenbach > > > > > wrote: > > > > > > For instance the hellcreek switch has actually three ptp > > > > > > hardware > > > > > > clocks and the time stamping can be configured to use either > > > > > > one of > > > > > > them. > > > > > > > > > > The sja1105 also has a corrected and an uncorrected PTP clock > > > > > that can > > > > > take timestamps. Initially I had thought I'd be going to spend > > > > > some time > > > > > figuring out multi-PHC support, but now I don't see any > > > > > practical reason > > > > > to use the uncorrected PHC for anything. > > > > > > > > Just out of curiosity: How do you implement 802.1AS then? My > > > > understanding is that the free-running clock has to be used for > > > > the > > > > > > Has to be? I couldn't find that wording in IEEE 802.1AS-2011. > > > > It doesn't has to be, it *should* be. That's at least the outcome we > > had > > after lots of discussions. Actually Kamil (on Cc) is the expert on > > this > > topic. > > According to 802.1AS-2011 (10.1.1): "The LocalClock entity is a free- > running clock (see 3.3) that provides a common time to the time-aware > system, relative to an arbitrary epoch.", "... All timestamps are taken > relative to the LocalClock entity". The same statement holds true for > 802.1AS-2020 (10.1.2.1). Nice having you part of the discussion. IEEE 802.1AS-rev draft 8.0, clause F.3 PTP options: The physical adjustment of the frequency of the LocalClock entity (i.e., physical syntonization) is allowed but not required. In fact, even if that wasn't explicitly written, I am having a hard time understanding how the "B.1.1 Frequency accuracy" requirement for the LocalClock could be satisfied as long as it is kept free-running. Otherwise said, what should I do as a system designer if the LocalClock's frequency is not within +/- 100 ppm offset to the TAI frequency, and I'm not allowed to correct it. By the way, how would you see the split between an unsynchronized and a synchronized PHC be implemented in the Linux kernel? Thanks, -Vladimir
