[Coco] Re: Mocha & OS9
johncollyer at zoominternet.net
Wed Jan 28 10:32:24 EST 2004
I seen that too, but I'm not sure what it means.
I looked in the Disk Basic Unravelled Series
and it has a section about the FDC. Did you
look at this source?
----- Original Message -----
From: "Brad Grier" <bradgrier at cox.net>
To: <coco at maltedmedia.com>
Sent: Wednesday, January 28, 2004 9:59 AM
Subject: [Coco] Re: Mocha & OS9
> Robert Gault wrote:
> > Brad Grier wrote:
> >> I'm trying to get OS9 working in Mocha but I have a bug in the disk
> >> emulation. It *appears* the NMI interrupt is firing when it shouldn't
> >> be. My docs on the FDC are pretty sketchy - is there a flag in one of
> >> the registers that turns off the NMI?
> >> Thanks again,
> >> Brad
> > Hmmm, by definition non maskable means it won't turn off. There is a
> > Coco flag at $982 which is used by the NMI routine. If set the routine
> > rti's to the address at $983, else it just does a simple rti.
> > The 1793 and 1773 always generate interrupts on the completion of a
> > task. Controllers for the Coco feed that interrupt to the NMI line.
> > There is no switch for this connection.
> I downloaded the MESS source (I should have done this earlier). There's
> a comment in cococart.c that bit 5 of the control register at $ff40 not
> only controls floppy density but is an "NMI enable flag".
> I made the change and things progress further - there's still a problem
> somewhere though.
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