irq -1 issues on mac:
-1 comes from Vctl *v (v->irq)
Vctl defined in dat.h? (io.h?)
called via intrenable (see intrenable(9), trying to bind an interrupt handler)
- via PCArch archgeneric?
  - -> archinit?
    -> main() ? (in pc)
- when is non-generic arch used?