shaiko
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Please elaborate1 problem with Modelsim is that coverage merging is not accurate...
The most annoying thing about using it was that management made it a point that you had to show your coverage was over 95%
What you usually do is that you write N test cases to cover all N branches. So each test case covers it's respective branch. Finally you have to merge all the coverage results to get 100% coverage. But what I have observed with modelsim is that after merging individual results, you don't get a 100% result. What you will get is around 80 or 90%...
That's because the typical management types didn't pay attention during non-linear physics in kindergarten. 100% test coverage can only be 2 times as much work as 50% coverage, right? And possibly it's even less work than that factor of 2 due to economies of scale. ;-)The most annoying thing about using it was that management made it a point that you had to show your coverage was over 95%.
Yes this is how I've normally dealt with the problem, but its really annoying when management gets fixated on the latest Holy Grail of verification, because of some smooth talking sales person says it will fix all the problems, without understanding the implications of using it. Then it takes the engineering staff months to convince management it wasn't the panacea they thought it was.But yes, I know the sort of problem. And in a previous job I got so many of those on a daily basis that I learned to not fight it. Go with the flow. You want a 99.9999% guarantee of Whatever It Is Today? No worries, we can do that. The consequences of that request are such & such, and it will cost you roughly this much. Usually followed by a WHAAAAAAAT?!? Give a rough breakdown of the time & costs and that's that. And after they settle down a little you explain a couple of more reasonable strategies + time/cost, and then your favorite management person gets to choose which one he wants. You sure? Yes. Confirm over e-mail with your management dude on the CC (aka no backpedaling) and Bob's your uncle.
I found that usually by adressing the mismatch between expectation & reality you mostly can fix this sort of problem. There's always the difficult person but those are significantly less than 50% of the PMs I've had to deal with.
Yes this is how I've normally dealt with the problem, but its really annoying when management gets fixated on the latest Holy Grail of verification, because of some smooth talking sales person says it will fix all the problems, without understanding the implications of using it. Then it takes the engineering staff months to convince management it wasn't the panacea they thought it was.
The mark of a true experienced person. ;-)I just realized I'm probably coming off as a cynical old fuddy duddy. ;-)
Another one to watch out for is daily TNS figures from your overnight seed sweep.
The problem is you can cut the numbers down quite quick with some sweeping timing specs or area constraints. But you get the pain when the last few ns refused to go down by much on a day to day basis.
That's odd. And "odd" is the polite form of "big fat bug" if what you say really is what is happening. Are you certain you did cover all cases and merged them correctly? Because running seperate test cases and then adding up all the bins to see what branches got hit is pretty much an elementary action for a test coverage tool IMO.
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This is what my experience has been. Maybe others can also share their experiences with Modelsim coverage here..
Curious. Were there any particular methods you used to work around this behavior?This is what my experience has been. Maybe others can also share their experiences with Modelsim coverage here..
Curious. Were there any particular methods you used to work around this behavior?
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