Chris asked me about adding an interrupt in the PACSAT software.  I answered him, (the answer is the same for PACSAT and Golf) but then realized that this is probably not well documented anywhere.  So for now, I cut and pasted the email to him and put it in a document in PacSatDocs/refernce (since it is originally a Golf and even Fox thing, I'll put the source there eventually).

This is not an emergency for you to read unless you are adding GPIOs or interrupts. It sounds complex, but it is sort of a reasonably simple abstraction of GPIOs and interrupt that works on both the LIHU and the RT-IHU.  The complexity comes because  the two processors not only interrupt stuff that is quite different from each other, but not really the same as the abstraction itself!