[Coco] How to mod MPI for ganged interrupts

[Brett Gordon]

Robert,

I'm trying to run a rs232 pak and my SDC together simultaneously.  My rs232
handling needs to use the CART(FIRQ) interrupt.  The SDC, in harddrive
mode, doesn't use/need interrupts, but does use the MPI switched $ff40
addresses.  This means i do have to have it's slot selected in order to
talk to it, which has the unfortunate side effect of turning off the CART
line from the rs232 pak.  My theory is: the thread that is accessing the
SDC should be fully interruptable (and justly so) by the more time
sensitive rs232 pak.

I suspect that I can affect this mod by simply jumpering the some of the
interrupt lines coming into the interrupt mux chip from the different slots.

I remember hearing of old-timers doing this to make a better performing os9.

And I thought I would ask here, before I spend an hour or two thunking over
schematics, and risk possibly blowing up my MPI...

(Looking at you Gene Hesket) :)

Cheers, brett