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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.
From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: Monday, December 29, 2008 6:02 PM
Subject: Re: [802.3BA] XLAUI / CAUI Ad Hoc
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
From: Ryan Latchman
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.
From: Ali Ghiasi