On Tue, 2016-11-08 at 22:49 +0100, Richard Cochran wrote: > This series expands the PTP Hardware Clock subsystem by adding a > method that passes the frequency tuning word to the the drivers > without dropping the low order bits. Keeping those bits is useful > for > drivers whose frequency resolution is higher than 1 ppb. >
Makes sense. > The appended script (below) runs a simple demonstration of the > improvement. This test needs two Intel i210 PCIe cards installed in > the same PC, with their SDP0 pins connected by copper > wire. Measuring > the estimated offset (from the ptp4l servo) and the true offset (from > the PPS) over one hour yields the following statistics. > > > > > | Est. Before | Est. After | True Before | True > > After | > > --------+---------------+---------------+---------------+-------- > > -------| > > min | -5.200000e+01 | -1.600000e+01 | -3.100000e+01 | > > -1.000000e+00 | > > max | +5.700000e+01 | +2.500000e+01 | +8.500000e+01 | > > +4.000000e+01 | > > pk-pk: | +1.090000e+02 | +4.100000e+01 | +1.160000e+02 | > > +4.100000e+01 | > > mean | +6.472222e-02 | +1.277778e-02 | +2.422083e+01 | > > +1.826083e+01 | > > stddev | +1.158006e+01 | +4.581982e+00 | +1.207708e+01 | > > +4.981435e+00 | > > Here the numbers in units of nanoseconds, and the ~20 nanosecond PPS > offset is due to input/output delays on the i210's external interface > logic. > > With the series applied, both the peak to peak error and the standard > deviation improve by a factor of more than two. These two graphs > show > the improvement nicely. > > http://linuxptp.sourceforge.net/fine-tuning/fine-est.png > > http://linuxptp.sourceforge.net/fine-tuning/fine-tru.png > Wow, nice! I'll take a look at the actual patches in a few minutes, but this is a really nice improvement! Thanks, Jake > > Thanks, > Richard > > Richard Cochran (3): > ptp: Introduce a high resolution frequency adjustment method. > ptp: igb: Use the high resolution frequency method. > ptp: dp83640: Use the high resolution frequency method. > > drivers/net/ethernet/intel/igb/igb_ptp.c | 16 ++++++++-------- > drivers/net/phy/dp83640.c | 14 +++++++------- > drivers/ptp/ptp_clock.c | 5 ++++- > include/linux/ptp_clock_kernel.h | 8 ++++++++ > 4 files changed, 27 insertions(+), 16 deletions(-) >
