[SI-LIST] Re: On time to vm
- From: "Abe Riazi" <ariazi@xxxxxxxxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 12 Mar 2004 10:52:41 -0800
Dear S. Lakshmi:
Frequenclty, it is desirable to enable the " V(m) Correction " in XNS, for
efficient
computaion of flight times (needed for setup and hold timing margin
calculations).
However, it is important to ensure that the low_to_high and high_to_low
TIME_TO_VM parameters in the model's DRIVERSPEC are accurate; and the rise
and fall delays for the net (as reported in the .idd, .rep, and .gen files) are
error free.
There are also cases where it is preferable to disable the " V(m) Correction "
.
For instance, it seems to me that when evaluating timing margins for
differential
pairs, it is often advantageous to first manually measure the rise and fall
delays utilzing
the XNS (or TLC) cursors and then subtract the rising and falling components of
the
drivre's TIME_TO_VM parameter to obtain the desired flight times.
When flight time values are accurately determined, it is possible for some of
the results
to be negative and this is acceptable.
Best Regards,
Abe Riazi
ServerWorks
-----Original Message-----
From: Lakshmi S - CTD, Chennai. [SMTP:Lakshmi_s@xxxxxxxxxxxxxxx]
Sent: Thursday, March 11, 2004 4:15 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] On time to vm
Hi,
Pre route SI Analysis using XTK gives negative minimum delays and positive
maximum delays. There is a large variation between the two (Ex :
-0.493ns(min delay) and 0.55ns(max delay)). I've enabled vm correction.
As I want to know just the trace delay from the driver to the receiver, I do
not understand whether to enable time to vm correction.
Could anyone please clarify ?
Thanks and regards,
S. Lakshmi
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