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help! about multipal values in sdf file

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alanzheng

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help! about sdf file

get slow.sdf file from back-end, eg:

CELL......
IOPATH I ZN (0.197:0.197:0.197) (0.225:0.225:0.225)

...
TIMING CHECK
HOLD (posedge D) (posedge CP) (-0.157:-0.157:-0.157)

I have two question:
1. why has two value for IOPATH? what's meaning for each?
2. why the timingcheck is negtive value?

Thanks!
 

shelby

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help! about sdf file

1. The the two values are for rise/fall timing.
2. This means data must be held until 0.157ns before the next clock edge.
To help explain ...
Imagine your hold time is 0. Now add buffers to you D path INSIDE your FF. This will now make your CP to D hold requirement negative.
 

alanzheng

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Re: help! about sdf file

I got it. Thanks!
 

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