What does the term "corner case" refer to when it comes to design verification?

[matrixofdynamism]

What does the term "corner case" refer to when it comes to design verification?

I am aware of the term corner when it comes to static timing analysis. We find the combination of process, temperature and voltage which shall produce the fastest circuit and the combination which shall produce the slowest circuit. We then find out the propagation delays across paths and through cells for these two corners and calculate the slack for setup and hold time.

I have come across a document on SystemVerilog which states: "Before you write the first line of test code, you need to anticipate what are the key
design features, corner cases, and possible failure modes."

I do not understand what does corner case refer to here since this is not timing analysis, rather it is something different.

 

[sharath666]

Re: What does the term "corner case" refer to when it comes to design verification?

Corner cases here refers to functional verification.
Whenever you start FV, you know which are the direct cases. But there are cases which you do not anticipate. You may need a lot of expertise on the functionality of the core in order to think of this case. These cases are called as corner cases.

 

[matrixofdynamism]

Re: What does the term "corner case" refer to when it comes to design verification?

hmm... that does not seem to have made much sense. Is there some document that I can read that will describe this topic in detail?

 

[dave_59]

Re: What does the term "corner case" refer to when it comes to design verification?

A corner case is just jargon for a rare occurrence of interest. I don't know if you have ever painted a room, or cleaned the floor, but the corners are the hardest parts part to get into, but you still have to cover them as well as any other part of the room. That is just like your static timing analysis - you are looking at extreme ends of your range.

It's the same with functional verification, you are looking for the extreme stimulus conditions that will stress your design the most.

 

[matrixofdynamism]

Re: What does the term "corner case" refer to when it comes to design verification?

Thank you teacher Dave. It seems that this means that it is actually not always obvious what a corner case for a design would be. It depends on each design. There may be many corner cases or just a few. Unlike the case of Timing Analysis, the corner cases in the case of verification may even be subjective.

I have seen an example of a FIFO where the corner cases were when the FIFO is full, and when the FIFO is empty. Over the course of simulation if these two cases are also excercised than all cases in between would be exercised as well.

This made complete sense with what you have not explained. However, if we take a more complex example like an MP3 player, it would be not be completely clear what the corner cases are. The design engineer shall have to figure that out.

This much is now clear. Thank you.