SignalTapII

In an ideal scenario, you never use SignalTap. Instead you simulate the design, fix all issues there, and the hardware just does what the sims show.

I've never seen an ideal scenario though. Something doesn't work, sims don't catch it, and SignalTap is the only way to get in there and figure out what's going on.

One thing I like doing is having pre-determined tap points. These are basically locations where the data can be captured and you have a good understanding of what it should look like. You might want to put keep attributes on combinatorial nodes so they can be tapped post-fit. Then, if something goes wrong, you can hook signaltap up to that location, monitor it, and determine if the data is good at that point or not. It's definitely up front work that may not be necessary at the end, so up to you on how much time you want to spend.

Also, don't forget that you can put your top-level partition to Post-Fit, which locks down the whole design, and your SignalTap is a separate partition(by default), so you can tap nodes and monitor them without having to re-place-and-route the whole design. This is useful for quicker SignalTap implementations, and is extremely useful for problems that are build dependent, i.e. where some seeds show the problem and others do not.