A89: Memory Indirect Postindexed [Addressing] Mode

To: <assembly-89@lists.ticalc.org>
Subject: A89: Memory Indirect Postindexed [Addressing] Mode
From: "Scott Noveck" <noveck@pluto.njcc.com>
Date: Sat, 15 Apr 2000 22:45:28 -0400
Reply-To: assembly-89@lists.ticalc.org


Here's a question for anyone who _really_ knows their 68k well.  I guarantee
it'll confuse the heck outta everyone here.

How do you use "Memory Indirect Postindexed [Addressing] Mode"???  The
motorola syntax is:

([bd,An],Xn.SIZE*SCALE,od)    [all 4 user-specified values are optional]

which can be found on page 2-11 of the Programmer's Reference Manual, along
with a load of motorola technical terms and a pretty flowchart.  It appears
to use two levels of indirection, although I can't find any realistic use
for it (maybe a C compiler can?)

oh, and get this - it allows for up to FIVE extension words, or a single
instruction of MORE THAN 12 BYTES!

if you use 'bsr routine' with this code, I THINK it should put $FFFFFFFF in
d1.  I'm not sure if it assembles, but it seems to fit what the book says.
Can someone tell me if this would work, or, if not, what the hell this
addressing mode does and why it exists?

routine:                        ;all this should just be "st d1"
 move.l d0,-(a7)                ;save d0
 lea label1,a0                  ;base memory address
 move.l #2,d0                   ;number of [words] to be added later
 move.l (4,a0,d0.l,4),d1        ;first operand should be (label3) =
$FFFFFFFF
 move.l (a7)+,d0                ;restore d0
 rts                            ;return

label1:
  dc.l 0
  dc.l label2                   ;label1 + 4

label2:
 dc.l 0
 dc.l 0
 dc.l 0                         ;label2 + (2 * 2)
 dc.l label3                    ;label2 + (2 * 2) + 4

label3:
 dc.l $FFFFFFFF


    -Scott

Follow-Ups:

A89: Re: Memory Indirect Postindexed [Addressing] Mode

From: "Kaus" <kaus@cybrzn.com>

Re: A89: Memory Indirect Postindexed [Addressing] Mode

From: Olle Hedman <oh@hem.passagen.se>