[hatari-devel] Mega STe registers

npomarede at corp.free.fr npomarede at corp.free.fr
Sun Feb 28 22:34:59 CET 2010


On Sun, 28 Feb 2010, Jerome Vernet wrote:

> Le 28/02/10 20:56, Eero Tamminen a écrit :
>> Hi,
>> 
>> I just noticed that Oxyge's Calimer-O demo:
>> 	http://leonard.oxg.free.fr/demos/atari/CALIME_P.zip
>> 
>> Gives following when loading:
>> 	M68000 Bus Error at address $ff8e21.
>> 
>> This is MegaSTE cache/processor control register.
>> 
>> Maybe it should be emulated e.g. with a dummy function?
>>
>> 
> Does Hatari handle 16/8 Mhz software switch for the MegaSTe ?
>
> Jerome

The demo is doing clr.b $ff8e21, which will disable the cache and set cpu 
freq to 8 Mhz instead of 16 on a megaste.
So, this is only needed in case you boot Hatari in MegaSte mode (we don't 
have such a mode as this just means using 16 Mhz cpu).

For the sake of completness, we could emulate this but this means we 
should have a setting to explicitly set the system to 'mega ste', else 
this register should not be emulated.

But when it comes to watching demo, I'm not sure it's that important for 
now, as only very few demos would run at 16 MHz, the user is certainly 
already using a 8 MHz cpu.

Nicolas


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