Xref: utzoo comp.sys.amiga:25978 comp.sys.amiga.tech:2646
Path: utzoo!utgpu!watmath!clyde!att!rutgers!gatech!purdue!decwrl!labrea!polya!rokicki
From: rokicki@polya.Stanford.EDU (Tomas G. Rokicki)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech
Subject: Re: BLITTER-NASTY
Keywords: BLITTER,NASTY,HOW
Message-ID: <5433@polya.Stanford.EDU>
Date: 2 Dec 88 22:49:08 GMT
References: <143@sluga.UUCP>
Reply-To: rokicki@polya.Stanford.EDU (Tomas G. Rokicki)
Organization: Stanford University
Lines: 28


  Is it anyone out there who knows how the blitter nasty function works.
  Me and a friend are making some games for the amiga,but when we tried to
  speed up the games by turn on blitter nasty,we didn't see any change
  at all.

Normally, the blitter runs essentially full-out, unless the processor
has been blocked from a memory access for so many consecutive cycles
(3?), in which case the processor is given a single cycle.  The nasty
mode just makes sure the processor doesn't even get these cycles.
  
  In the hardware manual it say's that if you turn on blitter nasty,the 
  processor will have no(almost) time at all,and if that's true then
  we wouldn't have to do a Blitter-Ready-Loop before starting with the 
  next bitplane.                                                         

Not really true; many blitter functions (line draw and many `normal'
blits) don't use all possible DMA cycles.  Line draw, for instance,
does a single read and a single write every four possible memory
cycles.  The processor could get in on the other cycles.

A blitter-ready loop would only be unnecessary if the blitter were
in a mode where all possible DMA cycles are taken (a three-source
one-destination blit, for instance), blitter nasty was used, and
the processor was doing fetches from CHIP RAM.  In other words,
almost never, and I would certainly never recommend it.

-tom