I have trouble syncing to Linux systems using PTP.
Setup:
Two PCBs with a BegleCore module and a DP83640 PHY are connected with each other over Ethernet. One board should act as the PTP master, the other as the slave.
Debian 10, Kernel: 4.19.94
Driver for the Phy is loaded.
Using linuxptp v3.1
On the master system I run the command:
sudo ptp4l -i eth0 -f linuxptp/configs/configMaster.cfg -m
On the client system I run:
sudo ptp4l -i eth0 -f linuxptp/configs/configslave.cfg -m
Content of configMaster.cfg:
[global]
serverOnly 1
BMCA noop
Content of configSlave.cfg:
[global]
clientOnly 1
BMCA noop
step_threshold 1
This results in the following output on the slave:
ptp4l[438753.396]: selected /dev/ptp0 as PTP clock
ptp4l[438753.409]: port 1 (eth0): INITIALIZING to SLAVE on INIT_COMPLETE
ptp4l[438753.414]: port 0 (/var/run/ptp4l): INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[438753.418]: port 0 (/var/run/ptp4lro): INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[438754.075]: port 1 (eth0): new foreign master 304511.fffe.0ff048-1
ptp4l[438758.074]: selected best master clock 304511.fffe.0ff048
ptp4l[438762.072]: master offset 2426120726467 s0 freq -261066 path delay 15040
ptp4l[438762.074]: selected best master clock 304511.fffe.0ff048
ptp4l[438765.074]: master offset 2426120697575 s1 freq -270698 path delay 15156
ptp4l[438767.072]: master offset 2426120678191 s0 freq -270698 path delay 15156
ptp4l[438768.075]: master offset 2426120668273 s1 freq -280618 path delay 15830
ptp4l[438769.072]: master offset 2426120658469 s0 freq -280618 path delay 15830
ptp4l[438770.073]: master offset 2426120648789 s0 freq -280618 path delay 16022
ptp4l[438771.076]: master offset 2426120639057 s1 freq -290350 path delay 16022
...
The reported offset is approximatly 40 min. Before running ptp4l I had set the PTP clocks in the PHYs with testptp -s to the current system time. The PTP clocks were therefore actually within a few seconds of each other.
Each time ptp4l reports a "master offset s1 ..." it does step the PTP clock back by 40 min (checked with testptp -g). Yet the reported offset only changes by about 10 us.
I also looked into the network traffic with Wireshark and saw, that the Follow-Up messages from the master contain a timestamp that is by about 69 min of what the PTP clock in the PHY is set to.
After adding debug outputs to ptp4l I saw, that on the slave, the timestamp it extrats from the cmsgs returned from the socket is offset by about -27 min from what the client PTP clock actually is.
The difference from the false timestamps (+69 min) send by the master and the falsely read timestamps (-27 min) by the client results in the 40 min of assumed offset between the master clock and the client clock.
