On Wed, Mar 18, 2015 at 09:29:02AM +0100, Richard Cochran wrote: > I have seen good results with 1, 2, 4, and 8, packets per second on a > low end embedded system. With 128, some time stamps are dropped due > to hardware/driver constraints.
Here is a random metric from the boards on my desk. The CPUs are the TI AM335x, but using the DP83640 PHY as the PTP Hardware Clock. The slave is directly connected to the master with 1 meter cable over a 100 Mbit link. Measuring the edges of a 1 kHz output at various Sync rates, and with a DelayReq rate of 1 Hz, I see the following differences. Rate Offset ---------------- 2^0 +/- 75 ns 2^-3 +/- 25 ns 2^-4 +/- 20 ns 2^-5 +/- 20 ns As expected, increasing the DelayReq rate to 2^-5 makes no difference. So with this hardware, I have already reached the limit of synchronization performance. Increasing the Sync rate to 512 frames per second would not improve the picture. In contrast, using SyncE on the exact same hardware immediately yields an offset of +/- 1 nanosecond. (Actually, it probably is smaller, but I can't measure it with my lousy scope.) HTH, Richard ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Linuxptp-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linuxptp-users
