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| From: indi (all posts)
Date: 1999-09-27
Subject: Re: ECM+MCM black out mode...
|
>I haven't checked but I think it won't stop DMA. DMA starting and stopping
>event is tied to specific raster lines. I guess you want to make the screen
>a little bit smaller thus gaining some extra lines where no DMA is
>happening.
>You can do this by bringing the end of the screen window up some lines.
>An example:
>You wait for the raster line 0x0090 by polling $ff1d or by using a raster
>interrupt,
>and then write 0x00a0 into $ff1d/$ff1c. This will cause the end of the
>screen window
>to be 16 lines higher, so you will get 16 lines more where there is no DMA.
>After this you will wait for the line 0x00f0, and write 0x00e0 into
>$ff1d/$ff1c.
>This step is needed to put the line counter back where it should be, so no
>further events which are tied to the raster counter are moved from their
>place
>(like vsync etc...)
>And of course do this in a loop...
Ahh... good idea... I forgot about the writable raster... Since I only need a few lines, (and I already have a MCM+ECM blank IRQ) I can do blank it with this without too much of a problem... I think <g>
I'll have to do it on a real plus/4 first though.. My emulator isn't
100% reliable for proto-typing "tricks".. Its a bit too forgiving..
;-)
Just got my 8 baddie sprites following a path over a scrolling backdrop :-)
I forgot how much fun shoot-em-ups are to do! :-))))
Cheers,
Mike
^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^
Mike Dailly mike@scotch.demon.co.uk http://www.scotch.demon.co.uk
(Please remove the <REMOVE_ME> from my e-mail address when replying)
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