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Folks,
My concern is that specifying a chip to chip implementation
sets one set
of requirements focused on low signal power, low emissions,
and fairly
tightly specified channel definitions. A chip to
module implementation
set of requirements focuses on slightly greater signal
power, controlled
rise times, managed pre-emphasis and equalization, and a
broader range
of channel definitions that include
connectors.
If we succeed in a chip to chip implementation that does
NOT have
the chip to module implementation requirements considered,
then all
architectures will require intermediate transceivers on the
motherboard
between the protocol ASIC and the module, measurably
impacting
cost, complexity, reliability, and power. XFI was
focused specifically
on chip to ASIC implementations, using a module CDR to
improve the jitter
budget in the tightly constrained SR environment. As
such, it may be a
good starting model.
It would be better to have no chip to chip implementation
in this revision
of the standard if that implementation precludes chip
to module implementations
using a single definition of ASIC I/O
circuitry.
Bob Snively
408-835-4321 From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx] Sent: Monday, December 29, 2008 6:02 PM To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx Subject: Re: [802.3BA] XLAUI / CAUI Ad Hoc Hi
Ryan, You are right that the
nAUI chip to chip specification methodology in draft 1.1 can be leveraged to
build retimed modules. It just requires writing a chip to module specification
somewhere which specifies test points at the modules pins. The presentation you
sent is an excellent starting point for this and a lot of the XFI interface
specifications can be leveraged in writing the nAUI chip to module
specifications. Best Wishes for the New
Year to Everyone Chris From: Ryan Latchman
[mailto:Ryan.Latchman@xxxxxxxxxx] Hi Ali,
Chris, This is an important
discussion which needs to get resolved quickly. I would like to ensure
that XLAUI / CAUI maintains its broad market applicability as a simple retimed
interface. I don’t think the current specification methodology prevents it
from being leveraged to build retimed modules. I’ve put together the
attached material to show how retimed interfaces were specified in the past
(namely XFI). In XFI, you’ll notice that the Before Connector and After
Connector specs are similar. 40/100GbE modules may have an analogous
situation, depending on their size and electrical characteristics.
If we need to change
the XLAUI / CAUI specification, we need solid contributions on what needs to
change. Happy
Holidays, Ryan From: Ali Ghiasi
[mailto:aghiasi@xxxxxxxxxxxx] Chris |