On Wed, 29 Nov 2023 at 13:09, Miroslav Lichvar <mlich...@redhat.com> wrote:
> On Tue, Nov 28, 2023 at 03:34:54PM -0800, Richard Cochran wrote: > > On Tue, Nov 28, 2023 at 12:53:38PM +0100, Miroslav Lichvar wrote: > > > However, timestamping only sync messages has an advantage with very > > > large number of clients as they don't have timestamp each other's > > > delay requets and timestamping of sync messages is more reliable. > > > > Actually, in hardware is it much simpler and more efficient just to > > time stamp every frame. (The reporting can be selectable if the > > application doesn't care about some frame types) > > I think it depends on the hardware design, which impacts its cost. If > all hardware was able to accurately and reliably timestamp all > packets, we wouldn't need PTP. PTP was specifically designed to make > the hardware support as simple/cheap as possible. It separates event > messages from the rest and uses multicast messaging in order to reduce > the required timestamping rate. > Although PTP uses multicast. It is only a multicast MAC address, but it is not a real multicast group. As PTP messages are not forward to all peers as is. So PTP messages are actually unicast messages.using a multicast MAC address. > > Timestamping only sync messages on clients is just another trick to > reduce the required timestamping rate. The hardware can keep just one > timestamp at a time and it doesn't matter that if it takes 20 > milliseconds to read it over MDIO. It's good enough for clients, even > if there is a very large number of them on the same communication > path. > It Makes sense, yet using a PTP events filter is sufficient. The PTP service is a master or client, not both. So the amount of traffic you timestamp does not reduce by using a SYNC/ DELY versa events filter. Erez > > -- > Miroslav Lichvar > > > > _______________________________________________ > Linuxptp-devel mailing list > Linuxptp-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linuxptp-devel >
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