FPGA timming

Does anyone know of a good reference for timing concepts in synchronous FPGA designs. I know what false and multi-cycle paths are, but need some examples to understand how they occur in real designs.

Reply to
Kunal
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Let me elaborate a bit more. My understanding:

False Paths: Paths that are not timming critical but show up in the timming report with a -ve slack. Can't think of an example.

multi-cycle paths : Paths which can take 2 or more cycle to complete. But this would mean you gate the clock of the output/second resgiter in a multi cycle path so that it resgisters the right input after x clock cycles. Wouldn't that violate the sync design rules byt gating the clock and thus introducing skew? Aren't you better off pipelining it anyway, so that you get a result after every clock cycle after the inital pipeline latency.

Reply to
Kunal

Yes, if you can make timing that way, it's less trouble. The pipeline requires no special constraints. Multicycle does.

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-- Mike Treseler

Reply to
Mike Treseler

Or use a clock enable.

False paths are paths that you (as the designer) know aren't timing critical. (Such as a an output pin clocked on a 50 Mhz clock that drives an led).

Multicycle paths are paths that you (as the designer) know are allowed to take multiple cycles to resolve. For instance, if you have a section of logic running off a 100Mhz clock, but clock enables running to every flip-flop in that section of logic, then you know that every signal has two cycles to resolve before it will be sampled by the next stage.

Jeremy

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Jeremy Stringer

Reply to
Symon

Reply to
Symon

Reply to
Symon

I thought it would a good discussion to have on the FPGA group, rather than me asking experts and keeping it to myself. I am sure others new to FPGA design will have the same questions as well. It would be nice for a generic discussion to show up if someone typed 'FPGA timing' into the search box, that is if I didnt SPELL the topic wrong ! :-)

Reply to
Kunal

..and, you cheeky bugger, posting from Intel.com is not a good idea if you're slagging off people's arithmetic! ;-)

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Cheers, Syms.

Reply to
Symon

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