Community Functional Verification explain/correct my understanding between average/covered...

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explain/correct my understanding between average/covered in imc metrics

chetan somana

I'm working on the code coverage. Doing a metrics analysis by default we see overall average grade and overall covered. But when i do a block analysis on an instance i see overall covered grade, code covered grade, block covered grade, statement covered grade, expression covered grade, toggle covered grade.

As I dont know the difference I started to read the IMC user guide and came to know there are 3 things we come across while doing a code coverage local, covered, average

From my understanding

local - child instances metrics doesnt reach the parent level. For example, we have an instance Q and its sub instances like Q.a, Q.b. Block Local grade of Q can be 100% even when its instances Q.a and Q.b a block local grades isnt at 100%.

In the attached image there is formula 

The key difference between average and covered is the weights.

Average : Mathematically taking the above scenario where Q.a, and Q.b has 10 blocks each. Q.a has covered 8 blocks and q.b has covered 2 blocks. Now if we take the normal average it should be total covered/ totatl number = 8+2/10+10 yielding 50%. But when we add weights saying Q.a is 70% and Q.b is 30% the new number would be (8*0.7+2*0.3) / (10*0.7+10*0.3) resulting 62%. Because of the weights we see 12% bump.

Covered: there is no role of weights.

Among these 3 metrics i've changed my default view to this in the image to get more realistic picture when i do analyze metrics. Do you guys agree with the approach?

  • The weights only impact functional coverage. The Average grades are designed to highlight low grades in smaller child node (i.e. those with a small number of bins), whereas the Covered grades are a simple ration of the hit bins / total bins, which can hide small but un-hit items low down in the hierarchy.

    You would do well to look at both average and covered grades, and investigate why either type is not 100%.

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