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Tricky Clock Constraint Question

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GiuseppeLaPiana

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Hello All,

I am currently working on designing a DDR Interface from the ground up (no IP available, didn't want to go with Synopsys IP). The trouble I am having is defining clock groups.

I would like to set a clock that starts at the pin of my received strobe circuitry, this goes through some logic to delay the clock 1.5ns, from this port the clock fans out to a number of rising and falling edge flip flops. In the design I also have my system clock which comes off the board. The clocks are asynchronous. I am having a lot of difficulty setting the constraints for this situation using the commands
create_clock, set_clock_groups, and set_clock_latency. To make this slightly more difficult, the 1.5ns delayed clock is the output of a custom macro I have designed (this has with it its own lib/db). I believe the timing information is accurate, but the clock tree I am seeing does not reflect this information.

Has anyone worked with a similar problem?

Thanks for the help in advance!
 

ivlsi

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Have you resolved this problem?
 

yx.yang

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I think you'd better have good understing on timing constraint and SDC first.
Then you can refer to the following paper talking about DDR SDC in DC/PT:
1): Getting DDRs “write” – the 1x output circuit -- Paul Zimmer
2): Working with DDRs in PrimeTime -- Paul Zimmer
 

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