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Explanation of Deration and OCV

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Member level 2
Jul 25, 2005
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In our flow, we get an sdc from the frontend team and subsequently get additional margins.
1. My query is why does the SDC not have all the constraints in one file.
2. What is the concept of Deration(Setup/Hold) that needs to be applied?
3. What is OCV ? Again why is this included separately?
I am a backend person, so can you let me know in terms of a front end guys perspective what it would mean. Thanks !

set timing derate and on chip variation

OCV is on chip variation.
SSTA(Statistical static timing analysis) use OCV. Deration is coefficient of variation. If we use deriation we can use STA instead of SSTA.

on chip variation

1) Constraints do not all have to be in the same file. If you integrate multiple IPs into one design, you will have multiple constraint files that you load in separately. You can always do a write_sdc command to write them out into one file.

2) Derating is simply another way of adding margin to the design. This allows you to scale all delays by a certain percentage to increase margin. This is not an SDC constraint, but a variable to set within the tool run script.

3) OCV is a timing mode (like single or BC/WC). This allows you to use variation from the libraries in performing timing checks for ensuring worst case scenarios. Not sure what you mean by 'included separately'. This is not a SDC constraint, but a timing mode that you set in your tool run script.

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