Re: The Perfect Emulator?

[mjmahon@aol.com (Michael J. Mahon)]

Holger Picker replied:

>On 29 Sep 2003, Michael J. Mahon wrote:
>
>> One of the very few examples of a program which would require this
>> detailed accuracy for correct appearance is a program which uses
>> software to synchronize with the video refresh in order to perform
>> synchronous video mode switches.  Although there are a few demo
>> programs that use this technique, to my knowledge it has never been
>> used in commercially-released software.
>
>I'm sorry, Mr. Mahon, but this technique was actually used by a
>commercially-released software. The game 'Drol' (by Broderbund) shows a
>little animation sequence after level 3, which reads address $c050 for
>synchronization with the display. Some emulators that do not emulate $c050
>properly (mostly the case) or do not simply deliver random values as a read
>value (like AppleWin does) will hang.

<snip>

Thanks for letting me know!

I was never a big one for games, so my exposure is somewhat limited.
I do remember that there was a lot of "buzz" about the "vapor lock"
technique when it first became public, so I should not be surprised
that some game designers worked it into their games.  ;-)

I do recall several programs that did rapid page flipping for visual
effect.  I can easily imagine that this could wreak havoc with some
simpler display mapping schemes.

-michael

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