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by IshKebab
107 days ago
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> Getting waiver files reliably integrated into that flow has been problematic as those files are fragile, alter the RTL and they typically break as they refer to things by line number or expect a particular expression to be identical to when you did a waiver for it. Yeah last time I did this we used regexes but I really don't like that solution. I think the waiver should go in the RTL itself. I don't know why nobody does that - it's standard practice in software. SV even supports attributes exactly for this sort of thing. The tools don't support it but you could make a tool to parse the files and convert it to TCL. I've done something like that using the Rust sv-parser crate before. Tedious but not impossible. Also we found the formal waiver analysis tools to be very effective for waiving unreachable code, in case you aren't using those. Congrats on the silicon anyway! |
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Yes we had used them just never got it slickly integrated into the verification dashboard. We had used this kind of analysis for internal sign off. You could generate the waivers manually and check them in but that suffers from the problem discussed above. Plus as OpenTitan was a cross company project you run into EDA licensing issues where not everyone has access to the same set of tools and a UNR flow could be running fine on one partner's infrastructure but isn't workable everywhere for multitude of reasons.
The ideal would be the nightly regression would do the UNR flow to generate the waivers and apply them when generating coverage but as ever there's only so much engineering time to go around and always other priorities.