Re: XAUI AC coupling
Richard,
Then we would have to change the wording and scope of XAUI to be only a
pluggable module interconnect. I don't believe that this is in the best
interest of P802.3ae. The alternative solution is to not specify the
XAUI signal coupling method as is the case for all other 802.3
chip-to-chip interfaces.
Best Regards,
Rich
--
richard_dugan@xxxxxxxxxxx wrote:
>
> Rich,
>
> I would strongly oppose allowing DC-coupling in the spec since we would then
> have to pick a DC level. This would certainly hamper some technologies over
> others and lead to sub-optimum solutions, either now or in the future.
> Pluggable modules need to be AC coupled. Whether or not someone wants to
> use a proprietary chip-to-chip solution on a backplane is another issue, one
> that should be outside the scope of the standard.
>
> So given your choices below I vote for only AC-coupling.
>
> Regards,
>
> - Richard
>
> > -----Original Message-----
> > From: Rich Taborek [mailto:rtaborek@xxxxxxxxxxxxx]
> > Sent: Friday, September 22, 2000 10:20 PM
> > To: HSSG
> > Subject: Re: XAUI AC coupling
> >
> >
> >
> > All,
> >
> > By my count, I have 4 votes for allowing XAUI DC-coupling against 0
> > votes for requiring only AC-coupling. The 4 votes are:
> >
> > Ed Grivna - Cypress
> > Dawson Kesling - Intel
> > Jeff Porter - Motorola
> > Rich Taborek - nSerial
> >
> > Any other opinions out there?
> >
> > Best Regards,
> > Rich
> >
> > --
> >
> > "Jeff Porter (rgbn10)" wrote:
> > >
> > > Folks,
> > >
> > > I feel consensus emerging here.
> > >
> > > Rich writes
> > >
> > > > a) A XAUI implementer can always get away with AC-coupling and
> > > > AC-coupling details for XAUI are readily available;"
> > >
> > > and
> > >
> > > > That said, I'd be happy to go with (1) or (2).
> > >
> > > Dawson writes
> > >
> > > > An alternative is to mandate CAPABILITY for AC coupling.
> > This allows DC
> > > > coupling where compatible implementations permit, but
> > ensures that ALL
> > > > implemenations will interoperate via AC coupling.
> > >
> > > I agree. Specify the differential signal. Require the receiver
> > > to function *when* driven by ac coupled signals to provide a method
> > > that insures interoperability. After all, we've increased
> > baud rate, among
> > > other reasons, to permit ac coupling as an approach to
> > interoperability.
> > > Do not require ac coupling since dc coupling will often
> > work, and we've
> > > left a way to interoperate.
> > >
> > > The remaining technical work is to include in an
> > (informative) XAUI link
> > > budget (if we choose to explain how this could work) the
> > attenuation,
> > > skew, and jitter, etc. budgeted for ac coupling.
> > >
> > > Proposals and justification for this budget item?
> > >
> > > Jeff
> > >
> > > Rich Taborek wrote:
> > > >
> > > > Dawson,
> > > >
> > > > In terms of specsmanship, I believe that we have two
> > alternatives with
> > > > regard to coupling for XAUI:
> > > >
> > > > 1) Leave coupling out altogether as an implementation detail;
> > > > 2) Specify detail for both AC-coupling and DC-coupling.
> > > >
> > > > It sound like you're leaning towards (2) where I'm
> > leaning towards (1).
> > > > My argument is that (2) is a whole heck of a lot more
> > work than (1) and
> > > > may be more costly since compliance verification has some
> > non zero cost.
> > > > I believe that (1) works and is interoperable because:
> > > >
> > > > a) A XAUI implementer can always get away with AC-coupling and
> > > > AC-coupling details for XAUI are readily available;
> > > > b) A savvy XAUI implementer may save $$$, increase
> > reliability (fewer
> > > > components), increase signal fidelity (fewer vias), etc.
> > by going with
> > > > DC-coupling if possible given their component selection.
> > > >
> > > > The only other possibilities are not palatable to me:
> > > >
> > > > 3) Mandate AC-coupling;
> > > > 4) Mandate DC-coupling.
> > > >
> > > > That said, I'd be happy to go with (1) or (2).
> > > >
> > > > Best Regards,
> > > > Rich
> > > >
> > > > --
> > > >
> > > > "Kesling, Dawson W" wrote:
> > > > >
> > > > > Rich and all,
> > > > >
> > > > > I agree that it would be nice to avoid AC coupling if
> > we can still ensure
> > > > > interoperability.
> > > > >
> > > > > If we remove reference to coupling altogether, we must
> > add a common mode
> > > > > specification or definite logic levels; we cannot only
> > specify peak-to-peak
> > > > > swing as we are now doing and expect interoperability.
> > (All chip-to-chip
> > > > > interconnect spec's I know of specify either
> > DC-referenced logic levels or
> > > > > common mode and differential mode levels. Is there an
> > exception? We have
> > > > > avoided this by mandating AC coupling up to this time.)
> > > > >
> > > > > An alternative is to mandate CAPABILITY for AC
> > coupling. This allows DC
> > > > > coupling where compatible implementations permit, but
> > ensures that ALL
> > > > > implemenations will interoperate via AC coupling.
> > > > >
> > > > > -Dawson Kesling
> > > > > Intel Corporation, NCD
> > > > > 916 855-5000 ext. 1273
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Richard Taborek Sr. Phone: 408-845-6102
Chief Technology Officer Cell: 408-832-3957
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