linuxptp-users

[Linuxptp-users] Running ptp4l using UTC timescale with hardware time stamping

[Koehrer M. (ETAS/ESW5) <mat...@et...>]

Hi all,

we want to synchronize a couple of PCs. These PCs have to run for a couple of hours in a synchronized way.
We do not have a proper grandmaster clock, one of the PCs plays this role.
We use suitable Ethernet adapters (Intel IGB driver) to use the hardware time stamping.
In this setup the usage of the separate PTP time scale (with the offset of 35s against UTC) is really confusing.
Is it possible to force ptp4l to use UTC also for hardware time stamping e.g. by using an option (in the config file)?

That would ease everything dramatically!

Thanks for any hints on that!

Regards

Mathias

Re: [Linuxptp-users] Running ptp4l using UTC timescale with hardware time stamping

[Richard C. <ric...@gm...>]

On Tue, Feb 18, 2014 at 02:48:08PM +0000, Koehrer Mathias (ETAS/ESW5) wrote:
> Hi all,
> 
> we want to synchronize a couple of PCs. These PCs have to run for a couple of hours in a synchronized way.
> We do not have a proper grandmaster clock, one of the PCs plays this role.
> We use suitable Ethernet adapters (Intel IGB driver) to use the hardware time stamping.
> In this setup the usage of the separate PTP time scale (with the offset of 35s against UTC) is really confusing.
> Is it possible to force ptp4l to use UTC also for hardware time stamping e.g. by using an option (in the config file)?

I don't see an easy way to support this. Both the ptp4l and phc2sys
programs have code handling UTC-TAI conversion, but only for the
expected used cases. If you have a real PTP device, the assumption is
that you are also using the PTP timescale. We only use UTC when
absolutely required, for software time stamps.

You *could* try and hack this in, but I think it would be easier just
to maintain the PTP timescale in the PHC device.

Recent Linux kernels offer CLOCK_TAI, so you might consider using that
instead of CLOCK_REALTIME in your application.

Sorry,
Richard