[Coco] How to mod MPI for ganged interrupts

[Brett Gordon]

Gene,

As us youngins say: "You da man!"

Thanks so much.  I didnt even see the pull-ups.  This all jibes with what I
was guessing.  Its a nice feeling going into a project without uncertainty.

I'll probably desolder the resistors carefully and pull out a leg;  Throw a
scrap of paper explaining the mod in the case of the MPI, and tape a label
on her outside to properly warn the next owner.

Thanks again!

Sincerely,
brett

On Sat, Nov 16, 2019, 10:39 PM Gene Heskett <gheskett at shentel.net> wrote:

> On Saturday 16 November 2019 22:02:50 Brett Gordon wrote:
>
> > 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.
>
> You rang?  I'm one of those old-timers. :)
>
> There are 2 versions of its pcb that I know of, and the instructions,
> entirely from memory, are to bridge all 4 interrupts (pin 8 on the cart
> sockets IIRC) together.
>
> But this also parallels all 4 of the irq pullup resistors, which on mine
> are in a row in front of the cart sockets, so remove 3 of them else the
> combined pullup may be too much for just one cart to pull down.  So get
> out your schematics and just cut 3 of the 4 in two. Done. Leaving all 4
> active will cause a mild video flicker with incoming rs232 data due to
> the excess current drawn.  And It may lead to a cart failure due to the
> excess currents drawn.
>
> > 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
>
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> If we desire respect for the law, we must first make the law respectable.
>  - Louis D. Brandeis
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> https://pairlist5.pair.net/mailman/listinfo/coco
>