functional coverage collection - what is collected?

[ljepson74]

While I am waiting for an answer from the simulator vendor, I think I can form a non-tool-specific question about my problem.

 

I am running a simulation which dies when I collect functional coverage.  I can turn on/off functional coverage collection and when it is on, at the very end of simulation, I get: "ncsim: *F,INTERR: INTERNAL EXCEPTION".  It seems to be that while coverage is gathered, the problem occurs.

 

I can run tests which flow thru some channels of the dut and don't have the problem, but thru a specific channel of the dut, I often encounter the problem.

 

question1: What is classified as functional coverage?   I'd like to leave functional coverage collection on and comment out all coverpoints/covergroups.  (Actually I think I have, or am close, and the error still occurs.)  So, I am wondering, what must I grep for to remove to be sure that functional coverage collection has no meaning? My thought is to divide and conquer.

Am I not just looking for "coverpoint" and "covergroup", but also "assert" (as some code might have assertion based functional coverage)?  Is there anything else?

 

question2: (This is perhaps a bit tool specific.)  If the -covdut, or scope of where coverage should be gathered is targetted to a sub-sub-module, would you expect that (possibly bad) coverage code at a higher level (or different area) would have zero affect on the coverage collection?  (I've unsuccessfully tried to leave functional coverage collection on, but to move the target-scope to a trival part of the design, to see if the problem goes away.)

 

[apfitch]

Assertions count as functional coverage (at least according to section 16.2 of 1800-2012). You can disable all assertions with $assertoff.  Otherwise "it's probably a tool issue". 

 

I don't have any other ideas re your question 2.

 

regards

Alan

[ljepson74]

Thanks, Alan.  This did turn out to be a tool issue.  (When collecting coverage at the end of the test the crash happened.  If we stepped thru the code and periodically collected coverage at a few points in the sim, including the end, there was no problem.)

  An update to the next/latest patch fixed this.

 

 

regarding 1,2

1. Note to self: it seems functional coverage is specified by coverpoints and some assertions (depends upon how used)

An AE showed me a Cadence commandline option, -covcglog, to see what code the tool is considering as functional coverage.  I haven't explored it much yet though.

 

2. While I'd like to explore this more to find out what functional coverage item prompted the problem/coverage-collection-crash (if it could be tied to a specific one), I must move on with other tasks.