Re: [Linuxptp-users] Dynamically sync clocks with phc2sys depending on master/slave

[Peter B. <pe...@be...>]

Hi again,

> phc2sys has an automatic mode.  See the man page for details.

I have some follow up question as I still can not see that I get this 
correct. I hope some experienced linuxptp users can help out. I can not 
get sync between CLOCK_REALTIME and PHC as I expect.

I have two devices connected through a AVB Switch running gPTP config 
like the example from the repo. Only changed priority to 246 in order to 
become master instead of the AVB Switch. Both devices runnin glinuxptp 
version 3.1.1. Here is the config file used for ptp4l:

   #
   # 802.1AS example configuration containing those attributes which
   # differ from the defaults.  See the file, default.cfg, for the
   # complete list of available options.
   #
   [global]
   gmCapable               1
   priority1               246
   priority2               246
   logAnnounceInterval     0
   logSyncInterval         -3
   syncReceiptTimeout      3
   neighborPropDelayThresh 800
   min_neighbor_prop_delay -20000000
   assume_two_step         1
   path_trace_enabled      1
   follow_up_info          1
   transportSpecific       0x1
   ptp_dst_mac             01:80:C2:00:00:0E
   network_transport       L2
   delay_mechanism         P2P

On the first device I start and configure the linuxptp applications like 
this:

   $ ptp4l -i eth1 -f gPTP.cfg
   $ pmc -u -b 0 -t 1 "SET GRANDMASTER_SETTINGS_NP clockClass 246 \
         clockAccuracy 0xfe offsetScaledLogVariance 0xffff \
         currentUtcOffset 37 leap61 0 leap59 0 currentUtcOffsetValid 1 \
         ptpTimescale 1 timeTraceable 1 frequencyTraceable 0 \
         timeSource 0xa0"
   $ phc2sys -a -r -r --transportSpecific=1 -E ntpshm

With this configuration this PTP device becomes master on the network. 
phc2sys starts to sync PHC from CLOCK_REALTIME. What I now expect is 
that CLOCK_REALTIME (in UTC) will be exactly 37 seconds behind PHC (in 
TAI) but I can not see this happen.

   $ date;phc_ctl eth1 get;phc_ctl eth1 cmp
   Thu Oct 14 08:56:37 UTC 2021
   phc_ctl[573.296]: clock time is 1634201797.174712670 or Thu Oct 14 
08:56:37 2021

   phc_ctl[573.303]: offset from CLOCK_REALTIME is 1472ns

The log file from phc2sys output like this:

   phc2sys[524]: [599.261] eth1 sys offset -37000001462 s0 freq      +0 
delay    875
   phc2sys[524]: [600.262] eth1 sys offset -37000001467 s0 freq      +0 
delay    875

As phc_ctl does not compensate for UTC-TAI as I interpret the code I 
expected to see the 37 sec diff in the output from that utility and in 
the log file I expect something close to 0 offset. I think I have some 
bad configuration in my setup. Can someone help me understand how to 
proper setup this in order to get a good sync on the master side between 
the clocks? And I assume that I can use the same setting on the slave 
device to get it correct in that end to? I also think it is strange I 
can not get better precision than around 1.4 ms between the clocks.

Thanks,
/Peter