Multicycle custom instruction repeated calls, hangs, signals

The sopc builder software used to cache the timestamp (or similar) from the board instead of re-reading it.

Quite possibly something similar still happens.

It is a shame that the Altera eample about using custom intructions just tells you how to click the buttons to add/remove the ones they supply.

The source for one that implements add would be more useful!

I wrote a combinatorial one that uses the 5 bit rB field to choose between various bit and byte reversals.