[Coco] Nitros9 high speed mode

[Joel Ewy]

Robert Gault wrote:
> Joel Ewy wrote:
>> Robert Gault wrote:
>>
>>> ...
>>>
>>> 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.
>>>
>> <snip>
>> I once wrote a program to take 3 DS-69B Digisector video digitizer files
>> <snip>
>> and write a 15-bit Targa high-color image from them
> ><snip>
>> I wrote the program in
>> C under OS-9 because it was a much better development environment (at
>> least for this kind of thing) than DECB.
> ><snip>
>
> Joel,
> There is nothing in your example that would necessitate dropping the
> 2MHz speed or leaving the 6309 native mode. So how does it relate to
> my quoted comment?
>
Robert,

Maybe I was misunderstanding your point.  I thought you were saying that
any program running in 6309 NitrOS-9 that needed to drop the clock down
and leave native mode would have to keep the interrupts masked (thereby
preventing multi-tasking) and prevent system code from running again (as
well as any other processes).  I thought you were implying that
preventing multi-tasking would defeat the whole purpose of using OS-9. 

My example indeed does not require slowing down the CPU clock or leaving
native mode, but it might require masking interrupts for long periods of
time while waiting to sync up with the camera to grab a pixel.  If that
were the case, it would also interfere drastically with multi-tasking. 
My point was simply that multi-tasking isn't the only feature that
distinguishes (Nitr)OS-9 from DECB, and while disabling multi-tasking is
without a doubt sub-optimal and to be avoided wherever possible, it
doesn't completely defeat every purpose of running a program in OS-9, as
even the stock floppy disk driver suspends multi-tasking.

But maybe you meant something different.

JCE
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