Newsgroups: comp.sys.amiga.advocacy
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From: rjc@wookumz.gnu.ai.mit.edu (Ray Cromwell)
Subject: Re: (Video) Hardware Idiots ?
Message-ID: <1991Jun10.074421.6782@mintaka.lcs.mit.edu>
Sender: news@mintaka.lcs.mit.edu
Organization: The Internet
References: <1991Jun9.0 <1991Jun9.060440.29078@leland.Stanford.EDU> <1991Jun10.065629.21255@marlin.jcu.edu.au>
Date: Mon, 10 Jun 91 07:44:21 GMT
Lines: 59

In article <1991Jun10.065629.21255@marlin.jcu.edu.au> cpca@marlin.jcu.edu.au (Colin Adams) writes:
>In article <1991Jun9.060440.29078@leland.Stanford.EDU> bard@jessica.stanford.edu (David Hopper) writes:
>>DON'T, don't EVER think that the blitter drags the system down.
>
>On the speed of the 030 vs the blitter.  A student here was using
>the blitter to copy screens around constantly for his graphics project
>on his Amiga 3000 and it was going a bit slow.
>
>I told him to try using CopyMemQuick and he got a 75% increase in
>speed.
>
>Nough said!

  This will only work on the A3000 and only for limited cases. Try getting
him to do it with some logic operations and masking/shifting.
From all accounts I have seen, a 25mhz 68030 is rougly 5 MIPS.
Assuming those 5 million instructions were all move's theoretically
the 030 could transfer 20 megs of data/sec if there was no bus
contention and using fast ram. (5 MIPS * 4 bytes per longword = 20meg)
Chip ram cuts this figure in half (the processor only gets access
every other cycle), and a 16bit bus cuts it in half again. So you
end up with 5 megs/sec on an A2000/500 030 equiped system with no
chip memory contention and NO logic operations. The blitter transfers
7.2 megs/sec in the same circumstances. On the A3000 you have 32bit
access to chip ram so you can copy 10megs/sec (25% faster than the
blitter) But if you try doign any logic operations, shifting, masking or
filling your performance would be greatly reduced whereas these
operations on the blitter don't hurt it's performance much.

 And I wouldn't want 100% of my CPU being eaten up to copy data, so it's
still better to off load work onto the blitter except in special
circumstances.(as in uncompressing a picture, scrolling text fields on
hi-res 16 color screens, decoding a disk buffer using checksums)

  The blitter isn't this little piece of trash that is no longer any
good because 68030's exist. And the mere fact that it takes atleast
a 68030 with a fast memory system just to beat it means it is still
_very_ useful for the less powerful machines such as 68000/010/20 based ones.
 
  A 68000 can't even get near the blitter's performance.

>>Dave Hopper      |MUYOM!/// Anthro Creep | NeXT Campus Consultant at Stanford
>>                 | __  ///    .   .      | Smackintosh/UNIX Consultant - AIR
>>bard@jessica.    | \\\///    Ia! Ia!     | Independent Amiga Developer
>>   Stanford.EDU  |  \XX/ Shub-Niggurath! | & (Mosh) Pit Fiend from Acheron
>
>
>-- 
>Colin Adams                                  
>Computer Science Department                     James Cook University 
>Internet : cpca@marlin.jcu.edu.au               North Queensland
>'And on the eighth day, God created Manchester'


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