Re: [Linuxptp-devel] [PATCH 3/5] gptp: minimal support

[Keller, J. E <jac...@in...>]

> -----Original Message-----
> From: Delio Brignoli [mailto:dbr...@au...]
> Sent: Monday, July 16, 2012 11:43 AM
> To: Richard Cochran
> Cc: lin...@li...
> Subject: Re: [Linuxptp-devel] [PATCH 3/5] gptp: minimal support
> 
> Hello Richard,
> 
> On Jul 16, 2012, at 8:29 PM, Richard Cochran wrote:
> > On Mon, Jul 16, 2012 at 10:44:15AM +0200, Delio Brignoli wrote:
> >> On Jul 14, 2012, at 7:04 PM, Richard Cochran wrote:
> >>> This code is on the receive path. The sender has sent a one step
> >>> packet. What harm is there in processing it?
> >>
> >> The patch does not skip processing it, it forces a two_step sync (i.e.
> expects and process a follow_up) as per 802.1AS.
> >
> > Can you please explain his this forces the master to send a two step
> sync?
> 
> This isn't about forcing the master. This is about always assuming sync
> occurs in two steps (sync + follow up) with gPTP. The 802.1AS standard in
> section 11.4.2.3 and Table 11-4 says that the value of twoStep bit should
> be ignored on reception and assumed to be true. gPTP supports *only* two
> step sync.
> 

The correct answer, then, would be to drop the packet with a warning that OneStep mode is not supported. The master *will not* respond with a proper packet, so gPTP will be waiting forever to receive the response it wants. It can't make the master do the right thing. It would be trivial to receive OneStep packets, and "support" them even though it isn't standard. Either way, you should do one of two things

1) Break the standard, and support receive of OneStep packet
2) Drop the packet and print a warning about OneStep being not supported during gptp mode.

You shouldn't magically treat it as a TwoStep packet without telling the user. (Since they could easily have hooked it up to the wrong type of master etc).

> Regards
> --
> Delio
> 
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