[Coco] Coco Digest, Vol 48, Issue 53

[Joel Ewy]

Paul Fitch wrote:
>  
>   
>> Message: 14
>> Date: Mon, 30 Jul 2007 20:49:04 -0400
>> From: Robert Gault <robert.gault at worldnet.att.net>
>> Subject: Re: [Coco] Nitros9 high speed mode
>> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
>> Message-ID: <46AE8700.40506 at worldnet.att.net>
>> Content-Type: text/plain; charset=us-ascii; format=flowed
>>
>> 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.
>>
>>
>>     
>
> Ok, now I'm more informed.  And I thank you all for your thoughts.
>
> ...
>
> I'm running the 6309 Nitros v030206 under emulation using MESS104.  When
> Mess starts it reports the emulated Coco3's speed as .89 mhz.  So that's the
> only actual number I've seen.  I'm wondering if the emulated Nitros9 is
> actually running in high speed tho, because how would MESS know to allow it?
>
>   
I think the emulator just emulates the clock circuitry of the CoCo such
that if you POKE &HFFD9,0 the emulated hardware will respond the way a
real CoCo does and executes instructions at twice the speed it otherwise
would.  I think the reason you see the ".89 mhz" is just that that is
the speed the CoCo (both real and emulated) runs at when you switch on
the power.  MESS may even have an option to run it at 1.78 from emulated
power on.  It's been a while since I played with MESS.  But that could
be the reason for the speed report on startup.
> ...
>
> >From what you all are saying, on a REAL coco, with a 6309, Nitros9 6309 runs
> in Native mode at 1.78 mhz.
>
>   
Yes indeed.
> I suspect that under emulation, it stays at a simulated .89 mhz, no matter
> what Nitros thinks.  
>
>   
I don't think that's the case, but I could be wrong.  Try an
experiment.  In ECB in MESS, do the high speed poke and see if it makes
the cursor flash at double speed.  If so, then the high speed POKE does
work, and the clock circuitry is emulated faithfully, so NitrOS-9 should
be running at (emulated) 1.78MHz.

JCE
> ...
>
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco
>
>