Re: [stella] some questions about the a2600

Subject: Re: [stella] some questions about the a2600
From: emooney@xxxxxxxxxxxxxxxx (Erik Mooney)
Date: Wed, 26 May 1999 02:14:54 GMT
>> > There are no interrupts on the 2600.
>
>but dont games usually have interrupt vectors stored at the end of the roms?

They have vectors, yes, but they're not really for interrupts.  The word
at address $FFFC is the address where the CPU will transfer control at
powerup, and the word at address $FFFA is the address where the CPU will
transfer control after hitting a BRK instruction.

>> You can do whatever you want at the beginning.. whenever you start
>> generating VSYNCs, the TV will pick up on it and start displaying.
>
>ah, so the hardware and television don't even begin displaying until VSYNCs
>are
>used...kewl

They'll start displaying right at powerup (actually, the TV even before
powerup - static, or whatever happens to be on channel 3).  But it doesn't
matter if it displays garbage or blankness for a few sixtieths of a second
before you get your VSYNCs rolling.

>> Yes.  I believe there was an 8K bankswitched version of the text adventure
>> Dark Mage, by.... <blanking>... Greg Troutman?  There's also been at least
>> a couple 6k bankswitched Supercharger games.
>
>well, i thought maybe i could use the f8 method of bankswitching by
>essentially
>creating two 4K files with code that could in essence be seperate roms, append
>one
>on top of the other, and then access locations $FFF9 and $FFF8 (since $1000
>and $F000 are the same to the 6507) to switch back and forth between 4K
>sections...
>thats the way i see it...you think that would work?

Sounds about like the standard method of writing bankswitched games.

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