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From: prz@hprnd.rose.hp.com (Paul Zimmer)
Subject: Checking Timing Relative To An Output
John,
How do you check setup/hold timing of your outputs relative to another
output YOU generate?
The specific case (and this must be very common), is a write_enable
strobe to an external RAM. You'd like to somehow create a clock object
at the write_enable output pin, and have synopsys calculate the timing
based on the prop delay. This doesn't appear to be possible.
What I'm doing now is budgeting. I pick a number for the min and
max arrival time of the write_enable signal, check this number,
and create two virtual clocks (one min and on max) based on this number.
The timing is then checked relative to the virtual clocks.
So far, this seems to work. But having to budget the signal timing
when synopsys KNOWS the actual timing is clumsy. Also, I expect it will
quickly become unwieldy when I start checking best-case as well as
worst-case timing. Anybody find a better way?
- Paul Zimmer
Hewlett Packard, Roseville
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