[Coco] Mocha & OS9

[Robert Gault]

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.