Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!well!ewhac
From: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Broken Sprite?
Message-ID: <11692@well.UUCP>
Date: 17 May 89 06:24:02 GMT
References: <2254@tahoe.unr.edu>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Distribution: na
Organization: Amiga Biotechnology Labs and Nuclear Test Grounds, Nevada.
Lines: 34
Quote: "OO BABY YEAH!  ROCK AND ROLL!  I KNEAD YOU LIKE FRESH PIZZA DOUGH!"

In article <2254@tahoe.unr.edu> roccom@tahoe.unr.edu (RoCCo mArtIn) writes:
>	I've noticed that using certain hacks such as "oing" and "friends"
>   creates a character that is smeared vertically across the screen.  I'm
>   assuming that these programs are using sprites of some kind.  Could
>   someone please let me know what the problem could be???
>
	Let me try and make this lucid yet terse so that those who know what
the answer is don't get bored.

	Every video line the Amiga generates is divided into a number of
slots.  In these slots, the custom hardware fetches needed information from
memory to do its thing.  Among these are DRAM refresh, floppy disk DMA,
audio DMA, sprite DMA, and display DMA.

	Now, if you use Preferences start dragging your screen to the left,
display DMA needs to happen earlier so that it can display bits earlier on
the video line.  If you pull the screen far enough left, the display DMA
will start eating up the DMA slots belonging to the other facilities.  The
first to go are the sprite channels, from sprite 7 to sprite 0.
Theoretically, you should be able to stomp the audio channels as well, but I
don't know of anyone who's done this.

	The cure for your sprite troubles is to free up the sprite slots
again by dragging your screen to the right.

	[ Note for picky people:  I have it on reasonably good authority
that the documented hardware stop that's supposed to prevent killing sprite
0 doesn't actually exist. ]

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Leo L. Schwab -- The Guy in The Cape	INET: well!ewhac@ucbvax.Berkeley.EDU
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