[Coco] enable no-halt disto driver

[Robert Gault]

Bob Devries wrote:
> The real truth of the matter is that the emulator doesn't *need* a 
> no-halt controller. 

Maybe it depends on the degree of emulation.

> Why would it? It already runs much faster than a 
> standard coco3, unless you have a really slow PC to run it on.
> 

Not completely relevant.

> The SCII controller was designed to get more speed out of a real coco3. 
> In that regard it works very well indeed.
> I don't know how much speed difference there is now between NitrOS9 
> running with a Disto SCII (and the correct driver), and with just a 
> standard controller, running the rb1773 driver. I would think there is 
> really not a huge advantage now.

The SCII and other no-halt controllers were designed to remove the need 
for the NMI and tight loop with IRQs turned off. This is what causes 
standard controllers to drop key strokes during disk I/O. Do I/O with 
enough data in halt mode and you should drop key strokes regardless of 
CPU speed.

I don't believe you could use the no-halt drivers with any emulator as 
none of them emulate controller on-board memory or internal I/O. They 
don't lose key strokes ( at least MESS doesn't ) but then they don't use 
the 1773 or 1793 controller either. The real question is do the 
emulators actually disable the emulated keyboard during NMI operation 
when emulating the Western Digital controllers.

> 
> -- 
> Regards, Bob Devries, Dalby, Queensland, Australia
 ><snip>