Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!uunet!microsoft!darekm
From: darekm@microsoft.UUCP (Darek MIHOCKA)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Blitter direct?
Message-ID: <71068@microsoft.UUCP>
Date: 5 Mar 91 19:51:54 GMT
References: <5187@mcrware.UUCP>
Reply-To: darekm@microsoft.UUCP (Darek MIHOCKA)
Organization: Microsoft Corp., Redmond WA
Lines: 47

In article <5187@mcrware.UUCP> erik@mcrware.UUCP (Erik Johnson) writes:
>I am currently working on an animation viewer that does its work during the
>VBI.  Right now copying an image to the screen using movem's takes
>approx 160,000 cycles or 1/50 sec (8Mhz), which is a little to much data to
>handle in under 1/60 of a second.  I would like to make a version of my
>viewer blitter-ready (make use of it, if it exists).
>
>Can I use the blitter directly to move the data in less time?
>
>Is it safe to even use the blitter during a vbi?

No. Unless you take precautions to make sure that the blitter chip is not
currently in use, you could be interrupting some other blitter operation.

>Does the blitter access memory on video or cpu access times (that is, can
>both the blitter and cpu write to memory at 8 Mhz each (interleaved)?

I don't know that. But don't expect a large speed boost. For straight
memory moves with no shifting or masking operations, the blitter is
almost the same speed as your MOVEM code. I have tried to get it to
go into hog mode, but that seems to interfere with interrupts (such as
mouse interrupts which you don't want to mask) so I can't say how much
faster it is possible to get it to run. Ideally, it takes 128000 clock
cycles to blit 32K of screen RAM, which is only about 20% faster than
what you're getting now.

>And lastly, how do I detect the presence of the blitter?

Xbios function 64 with a parameter of -1. Something like...

   move.w #$ffff,-(sp)
   move.w #$40,-(sp)
   trap   #14
   addq.l #4,sp

The return value in D0 tells you. Bits 0 and 1 will tell you whether
the blitter is present and if so, whether it is enabled or not. I don't
remember offhand which bit is which. It's documented in the COMPUTE
and ABACUS books.

- Darek

-- 
----------------------------------------------------------------------------
  Darek Mihocka, author of Quick ST 3.0.   All views expressed are my own.
  Branch Always Software, 14150 NE 20th St. Suite 302, Bellevue, WA  98007
----------------------------------------------------------------------------