Re: [Linuxptp-users] Using ptp4l on wireless device

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

On Fri, Oct 24, 2014 at 05:29:22PM +0200, Julian Scheel wrote:
> Hi,
> 
> I am trying to migrate from ptp2 to ptp4l currently. Using wired 
> networking I got everything to work quite well using software 
> timestamping yet and get very good results. But I also need sync via 
> wifi (I am aware the results will not be as good as via cable, but 
> through ptp2 I was able to achieve at least 100us accuracy).
> Now it seems that the wifi stack in recent linux kernels is not 
> supporting SOF_TIMESTAMPING_TX_SOFTWARE at all. But this seems to be a 
> hard requirement for using ptp4l with software timestamping, right?

Right.

> I am just wondering how ptp4l was running on a wireless device in this 
> discussion:
> http://permalink.gmane.org/gmane.comp.linux.ptp.user/295

Drasko (who started the topic) apparently hack Tx time stamping into
the wireless stack, but he did say how or where he did it, IIRC.

See also the other threads he started on May 31, 2013.

> I'd be glad about any hints how to get ptp4l working with a wireless 
> device. Actually I am using a rtl8192cu device right now.
> Are there some kernel patches around implementing 
> SOF_TIMESTAMPING_TX_SOFTWARE for wireless devices maybe?

None that I know of. Once or twice I looked at adding this into the
wireless code, but I could not find the right place to do it.

(but maybe there is some way to do it...)

Thanks,
Richard