[SI-LIST] Re: IBIS Timing Analysis
- From: "Beal, Weston" <weston_beal@xxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 9 Jun 2003 08:45:23 -0700
Ned,
The most correct method is to change the reference load in the IBIS file to
match the load used by the vendor when they measured the Tco of the part. For
PCI devices it is a bit more complicated, because the PCI spec reference load
changes for different corner cases. The IBIS spec was recently updated to
allow typ, min, max values for the timing reference load elements, but I don't
know of any simulators that take advantage of that feature yet for the
automatic timing derating. When I was faced with this PCI problem, I used a
single reference load and tightened the timing rules to compensate a bit for
the fact that I didn't use the second reference load. Then if I had a net that
didn't meet my tightened rule then I went back and checked it with the true
reference load (in an edited model) and the true timing rule.
Good Luck,
Weston
-----Original Message-----
From: ndempshe@xxxxxxxxxxxxxx [mailto:ndempshe@xxxxxxxxxxxxxx]
Sent: Monday, June 09, 2003 8:13 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] IBIS Timing Analysis
Greetings SI List,
I have a quick question.
I am analyzing timing with our board simulation tool.
The test load indicated in the IBIS model is not the same as the load provided
in the data
sheet and for the PCI bus signals - the PCI bus specified load.
When calculating flight times, the simulator is enabled to automatically
subtract out the
test load delay so that I do not double count the IO buffer delay when adding
flight time
to the datasheet clock to Q times.
Will the difference between the IBIS model test load and the data sheet test
load make
this timing budget technique inaccurate?
If this is a problem, are there any suggestions on how best to handle this?
Should I disable the automatic delay subtracting feature of the tool to obtain
flight
times which do not subtract out the test load buffer delay. Then simulate the
IBIS model
into the test load to obtain the buffer delay into the test load. Then,
subtract this
value from the simulator flight times in a separate spreadsheet to obtain more
accurate
flight times?
OR
Should I change the test load in the IBIS model to correspond to the datasheet
or PCI
specified load?
OR ???
Your help is much needed and appreciated.
Thanks,
Ned Dempsher
L-3 Communications
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