Xref: utzoo comp.sys.amiga:37152 comp.sys.amiga.tech:6249
Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!portal!cup.portal.com!thad
From: thad@cup.portal.com (Thad P Floryan)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech
Subject: Re: Need information about 68010.
Message-ID: <20625@cup.portal.com>
Date: 20 Jul 89 07:39:31 GMT
References: <1407@rivm05.UUCP> <116164@sun.Eng.Sun.COM>  <26405@agate.BERKELEY.EDU> <116365@sun.Eng.Sun.COM>
Organization: The Portal System (TM)
Lines: 50

Steve -Raz- Berry asks:

"
	... block moves. What kind of tight loop uses only three words?
"
regarding the 68010.  To keep things simple (and keeping within the spirit of
the copyright law permitting "extractions" for purposes such as this), on pages
264-265 of the book "68000,,68010,68020 PRIMER" by Stan Kelly-Bootle and Bob
Fowler (SAMS), we find:

"
The MC68010 automatically detects when certain 3-word instruction loops have
repeated more than one time, and then goes into loop mode.  In this mode, the
instructions are not repeatedly fetched from memory, as would occur during
normal operation, but are locked into the CPU pre-fetch queue and decode
register, and not fetched again.  If the loop is interrupted by any exceptions,
loop mode will resume after returning and going through two or more loop
repetitions.  Thus, simple loops such as the movement of a block of bytes, the
summation of a list of numbers, and the shifting of a group of numbers, can be
executed at speeds comparable to the speed of a single (for example, block move)
instruction.

The allowable loops consist of certain 1-word instructions followed by a DBcc
instruction .....
"

Certain forms of the following instructions are "loop mode-able":

MOVE, ADD, SUB, CMP, AND, OR, EOR, ABCD, ADDX, SBCD, SUBX, CLR, NEG, NEGX, NOT,
TST, NBCD, ASL, ASR, LSL, LSR, ROL, ROR, ROXL and ROXR.

See the book (and other similar ones) for more info.

Steve's comments re: the blitter neglect the fact the blitter will NOT operate
in "FAST" RAM; it is limited to CHIP ram.

If someone makes a peripheral card utilizing one of Motorola's 68000-family
dual DMA chips (or some other vendors' chips), many of the block move features
of the blitter can THEN be done in FAST ram.  People seem to overlook that DMA
can go "three ways":

	1) RAM to <something else>
	2) <something else> to RAM
	3) RAM to RAM

As to whether this is feasible on the (synchronously-clocked) Amiga is something
I have NOT investigated at all.  Something with more "free time" will, I'm sure,
have real fun exploring these (and other) possibilities!  :-)

Thad Floryan [ thad@cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]