[Coco] Nitros9 high speed mode

[Robert Gault]

Joel Ewy wrote:
> I think this thread is suffering from insufficient specificity.  :) 
 ><snip>

Boy did you hit the nail on the head with that comment!

The module that turns on the 2MHz, and native modes in Level2 6309 is 
Rel. There is no reason to go to 1MHz or emulation mode and these mode 
should not be changed without a VERY good reason.

Since the system does not expect the above to change, I don't think 
there is any test made for these changes. There is a shadow register on 
the system direct page, D.MDREG, which will tell you whether you are in 
native mode. If you have not studied the OS-9 defs, and already 
understand the direct page content, you should not consider any changes.

It is possible for user programs to revert to 1MHz and emulation mode 
with one important caveat. You can't let the system regain control until 
you return to 2MHz and native mode. That means all IRQs should be turned 
off, vectors saved, vectors redirected, speed and mode changed, and IRQs 
restarted. This completely defeats the point of using OS-9. You might as 
well write a stand-alone ml program to run from Disk Basic.