[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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