XGMII electricals
Implementing the XGMII concensus of the Task Force expressed through straw
polls in New Orleans is a problem. In fact, I would characterize the actions
we took in New Orleans to be an example of group think gone wild. We had a
comprehensive SSTL specification in the draft, but made the straw poll votes
to change on concepts, not proposed specifications.
There is no standard for HSTL at 1.8 volts (the preferred voltage per straw
poll), nor did the TF select any other parameters of the electrical
specifications. (Class I, 1.5 volt HSTL as specified in EIA/JESD8-6 is the
closest standardized alternative that the team working on clause 46 could
find). Because we couldn't find a standard to reference and the Task Force
didn't endorse a complete set of 1.8 volt specifications, there was no way
an HSTL electrical specification could be inserted into the draft without
adding a lot of technical material that hadn't been endorsed by the
committee. Therefore, all you will find in Draft 1.1 on HSTL is an editor's
note describing the situation.
Most discussion supports the idea that the XGMII electrical interface is for
near term usage (with continued use as an module to module logic interface
within a chip). Implemeters expect the electrical interface to be supported
by I/O devices in quick turn silicon libraries. Some participants in the
editorial session thought ASIC vendors might have a 1.8 volt HSTL derived
from the above referenced specification, but weren't sure of any vendors
supporting it (for inclusion in the standard it should be supported by many
vendors).
We have a similar problem with the clock alignment were the straw poll
endorsed a change without any specifications to implement the change (e.g.,
skew specifications).
As it now stands, I would vote against going to Task Force ballot. It would
be a shame for TF ballot to be delayed because of the absence of XGMII
electricals. I see three alternatives that would allow us to go forward to
TF ballot.
1. Return to the SSTL specifications of Draft 1.0
2. Reference HSTL at 1.5 volts per EIA/JESD8-6 and select from the options
within that specification.
3. Someone presents a detailed proposal including all appropriate
specifications (timing, thresholds, AC and DC characteristics, termination,
etc.)
As the clause editor, I will be proposing alternative 1 in Tampa unless
participants come through with presentations (sufficiently detailed to go to
TF ballot), and the Task Force endorses the specifications presented.
Bob Grow
Editor Clause 46