added ptp sync

[ZacharyTaylor]

Adds in setting to use ptp timesync on startup and rejects measurements until the sync happens.

To use ptp install with
sudo apt install linuxptp

edit the parameters for starting the service
sudo vim /lib/systemd/system/ptp4l.service

all you need to set is
ExecStart=/usr/sbin/ptp4l -i <your ethernet interface>
in my case ExecStart=/usr/sbin/ptp4l -i enp0s25

then start the service
service ptp4l start

and make it run on boot
sudo systemctl enable ptp4l

[helenol]

LGTM great! Thanks. Just have to remember to enable this on the helis. :)

[HannesSommer]

Awesome! There is a LIDAR using PTP? Sounds like Christmas to me :).

A note on @ZacharyTaylor suggestion of how to edit systemd's service config:
It is inadvisable to edit /lib/systemd/system/ptp4l.service directly, simply because this is the distributor's realm and might get overwritten with the next package update. Systemd has quite a sophisticated solution to that. It uses a layered configuration system. You can inject your modified version into a layer above by placing it at /etc/systemd/system/ptp4l.service. Even better is to use the drop-in feature by placing only the changed lines plus their section header into some file in /etc/systemd/system/ptp4l.service.d/.
The systemctl tool supports you in both cases with
systemctl edit --full ptp4l (creates a complete copy and lets you edit)
systemctl edit ptp4l (creates a drop-in file and lets you edit)

In any case (including editing /lib/systemd/system/ptp4l.service) you must run
systemctl daemon-reload or reboot for the change to take effect before you start the service.

[ZacharyTaylor]

Thanks for the tip about how to set up the service.
And yeah the lidar supports PTP out of the box, has made doing the timesync so much easier then usual

[dsb6063]

Hi appreciate the ptp info. We are trying to implement the cartographer 3D SLAM with ouster....and having problems. From reviewing the boards and manuals, it appears we need to be using a master clock either implementing a software or hardware version to produce time compatible epoch ros bags. Is this approach to implement a software ptp solution the hidden solution. I thought it was an option to implement ptp, but it sounds like more of a best practice.

[ZacharyTaylor]

If you are not fusing it with a second sensor I am surprised this is needed, however you can always start ptp4l using software timestamps with the -S option, which should work on pretty much any linux system.

[dsb6063]

I agree. We were trying to visualize/configure the TF tree and reading the recommend solution ouster-lidar#1

[eric-schleicher]

@dsb6063 Using ptp is an essential step and best practice if you have multi device or multi-host system.