phc2sys: Fix frequency estimation when synchronizing a PHC to the system clock.
When synchronizing a PHC to the Linux system clock (CLOCK_REALTIME),
the phc2sys uses the sysoff method, reversing the master and slave
roles.
The offset between a master clock and a slave clock is given by
offset = slave_ts - master_ts,
and the call to sysoff_measure() provides the 'offset' and 'slave_ts'
values. The needed local time stamp on the 'master' is given by
master_ts = slave_ts - offset,
but the code calcuates
master_ts = slave_ts + offset.
When passed to the servo, the local time stamp is used to estimate the
frequency offset between the two clocks before starting the main
synchronization loop. The effect of the bug may be seen with a simple
test. Here is a sample output with the existing code.
$ sudo testptp -d /dev/ptp1 -f 62400000
frequency adjustment okay
$ sudo ./phc2sys -m -q -c eth6 -s CLOCK_REALTIME -O0
phc2sys[90221.239]: eth6 sys offset 191001318 s0 freq -62400000 delay 5547
phc2sys[90222.239]: eth6 sys offset 253380897 s1 freq +8265884 delay 5507
phc2sys[90223.239]: eth6 sys offset -8301685 s2 freq -35801 delay 5487
phc2sys[90224.239]: eth6 sys offset -8297136 s2 freq -2521757 delay 5531
phc2sys[90225.239]: eth6 sys offset -5806117 s2 freq -2519879 delay 5542
phc2sys[90226.239]: eth6 sys offset -3317009 s2 freq -1772606 delay 5495
phc2sys[90227.240]: eth6 sys offset -1575231 s2 freq -1025931 delay 5505
phc2sys[90228.240]: eth6 sys offset -580249 s2 freq -503518 delay 5524
phc2sys[90229.240]: eth6 sys offset -107770 s2 freq -205114 delay 5519
phc2sys[90230.240]: eth6 sys offset 66298 s2 freq -63377 delay 5490
phc2sys[90230.881]: eth6 sys offset 86942 s2 freq -22844 delay 5495
And this is the output with the bug fix in place.
$ sudo testptp -d /dev/ptp1 -f 62400000
frequency adjustment okay
$ sudo ./phc2sys -m -q -c eth6 -s CLOCK_REALTIME -O0
phc2sys[90365.624]: eth6 sys offset 311912675 s0 freq -62400000 delay 5490
phc2sys[90366.624]: eth6 sys offset 374292766 s1 freq -31098 delay 5642
phc2sys[90367.624]: eth6 sys offset -3825 s2 freq -34923 delay 5617
phc2sys[90368.625]: eth6 sys offset 6 s2 freq -32240 delay 5564
phc2sys[90369.625]: eth6 sys offset 1241 s2 freq -31003 delay 5605
phc2sys[90370.625]: eth6 sys offset 1131 s2 freq -30741 delay 5600
phc2sys[90371.625]: eth6 sys offset 801 s2 freq -30732 delay 5621
phc2sys[90372.625]: eth6 sys offset 458 s2 freq -30834 delay 5640
phc2sys[90373.626]: eth6 sys offset 186 s2 freq -30969 delay 5598
phc2sys[90374.626]: eth6 sys offset 134 s2 freq -30965 delay 5599
phc2sys[90375.626]: eth6 sys offset 43 s2 freq -31016 delay 5595
phc2sys[90375.681]: eth6 sys offset -32 s2 freq -31078 delay 5541
This patch fixes the issue by correcting the calculation of the local
time stamp value.
Fixes: 8142da41b6
("phc2sys: Use reversed sysoff when synchronizing to system clock.")
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Reported-by: Cliff Spradlin <cspradlin@google.com>
Tested-by: Vladimir Oltean <olteanv@gmail.com>
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