[Coco] Re: Mocha & OS9

[John Collyer]

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?

John Collyer

----- 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.
> 
> Brad
> 
> 
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