[Coco] Re: Mocha & OS9
bradgrier at cox.net
Wed Jan 28 09:59:46 EST 2004
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,
> 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
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