MPIC ISU

[vb]

Greetings,

I am trying to write a BSP for an 8245 based device. One thing which
really gets me puzzled is the 'ISU' facility in
arch/powerpc/sysdev/mpic.c, there is also a notion of ISU-less
platforms, etc. I looked through the chip's programmer's reference,
even read the original AMD/Cypress OpenPIC specification - not a clue.

What is it, at the very least - what does ISU stand for?

I would really appreciate any hints,

thank you in advance,
/vb