RE: [SI-LIST] : An Interesting Presentation

Farrokh Mottahedin (Farrokh.Mottahedin@quantum.com)
Mon, 19 Apr 1999 13:48:37 -0700

I would like to add that data line skew should be as seriously examined as
clock line skew as Dr. Johnson suggests. With the advent of dual edge
clocking (as in Ultra ATA/33 & 66 and Ultra 160/m SCSI), the data lines can
switch as fast as the clock line, resulting in reduced setup and hold
budgets.

Farrokh Mottahedin
Quantum Corporation
(408) 324-7934
farrokh.mottahedin@quantum.com

> -----Original Message-----
> From: Abe Riazi [SMTP:ariazi@anigma.com]
> Sent: Saturday, April 17, 1999 9:53 AM
> To: 'si-list@silab.eng.sun.com'
> Cc: Walt Otto
> Subject: [SI-LIST] : An Interesting Presentation
>
> Dear All,
>
> Recently, I reviewed an interesting paper by Dr. Howard Johnson, which
> had been presented at DesignCon99. It is a PDF file (busarch.pdf)
> entitled: "Bus Architecture & Timing", available at the High Speed
> Design Web Site: http://www.signcon.com/
>
> The paper evaluates design difficulty of several different buses in
> terms of bus timing ratio defined by [( bus delay ) / (clock period)].
> The results are summarized below:
>
> Bus: PC-AT, Bus timing ratio: 0.008,
> Mode: Slow , Design: Easy;
>
>
> Bus: PCI, Bus timing ratio: 0.062,
> Mode: Skew, Design: -------;
> Bus: RAMbus, Bus timing ratio: 2.5,
> Mode: Distributed clock, Design: -------;
>
> Bus: Ethernet 10BASE-5, Bus timing ratio: 100, Mode:
> Time-space, Design: More difficult;
>
> In the final slide it is stated: " The ratio (bus delay)/(clock
> period) is a key indicator of bus design difficulty".
>
> Admittedly, I was surprised by the conclusion and method of analysis
> employed by this article. Here, a parameter dependent on the PERIOD is
> used to evaluate difficulty of bus design. It seems to me that
> "Critical Length" is preferable for appraisal of design (or simulation)
> complexity of a high speed bus architecture. The Critical Length Lc
> varies with the RISE TIME (i.e. Lc = k * Tr / D , where Tr is the Rise
> Time ), rather than with the period or frequency.
>
> Your comments are appreciated.
>
> Best Regards,
>
> Abe Riazi
> Anigma, Inc.
>
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