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Visitor cecillove
Visitor
3,090 Views
Registered: ‎09-27-2012

create_generated_clock in xdc for clock-enables

Hello: In my circuit, I have manaully transformed the gated clock to a flop enable the main clock. But now I can't seem to do a derived clock on this flop to specify constraints. Is there a way to specify create_generated_clock in xdc for this case even though now the gating logic is on the enable and the main clock is driving clock pin of the flop. I need to do this otherwise everything looks very critical to the tool.

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Teacher muzaffer
Teacher
3,075 Views
Registered: ‎03-31-2012

Re: create_generated_clock in xdc for clock-enables

For clock enables there is no need to generate a new clock. The system runs and is timed at the previous clock period. The interesting part for clock gating is that it is there for power and not for timing. The enable or gating of the clock usually comes in a non-periodic fashion so the output is not a generated clock of a different period but the original clock with random edges missing. If your gating is such that it guarantees at least x missing edges you can set a multi-cycle constraint. If you have a clock gate which works as a clock divider, you can do generated clock on it and when you convert it to a clock enable, you can use multi-cycle constraints to get a similar timing effect.
- Please mark the Answer as "Accept as solution" if information provided is helpful.
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Visitor cecillove
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3,063 Views
Registered: ‎09-27-2012

Re: create_generated_clock in xdc for clock-enables

hi, using multicycle -from <enable> -to  like this results in a lot of constraints and report_drc <timing_checks> complains that this is a lot of exceptions.

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