[SI-LIST] : An Interesting Presentation

Abe Riazi (ariazi@anigma.com)
Sat, 17 Apr 1999 09:53:24 -0700

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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