Synthesis results when testing for 'X' and 'U'

Rob · 2008-06-18T11:25:21+00:00

Sometimes it can be a bit tricky to stop 'X's and 'U's creeping intothe logic, especially at startup initialisation. If any logic tries touse these values then Modelsim cheerfully spawns lots of warnings.I've written a function called clean() which goes through a vector andreplaces any 'X' or 'U' values with '0'. This sorts out alot ofModelsim problems but I'm slightly worried about any unintendedeffects on synthesis. It does seem to synthesise without any problems,but can I rely on this for all synth tools or even future XSTreleases?Is a better solution to meticulously make sure all registers areinitialised when they are declared? or is it perfectly safe notnecessarily poor coding practise?CheersRob

Jun 18, 2008 20 Replies

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Mike Treseler 18 years ago

I don't use the GSR or SRL because they are non-portable and fussy. I save time by using an explicit reset of every register.

I agree with you there. I prefer saving time to saving some extra unused flops.

-- Mike Treseler

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Synthesis results when testing for 'X' and 'U'

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