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Atari coding BBS
| LINK + UNLK instructions |
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Posted by: Simon Sunnyboy / Paradize
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Mar,01.2009-14:02
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Insprired by a discussion on Atari-Forum, I experimented a bit with these instructions.
The main idea is to have easier access to my parameter stack.
I came up with the following test program which I traced with Bugaboo:
--snip--
;
; Test fuer LINK und UNLK Befehle
;
param1 EQU 0
param2 EQU 2
movea.l SP,A0
move.l #$CC000011,-(SP) ; param 2 (long)
move.w #$AABB,-(SP) ; param 1 (word)
bsr.s testroutine
addq.l #6,SP
illegal
testroutine:
link A6,#0 ; link stack frame to A6
move.w (8+param1)(A6),D0 ; get param1
move.l (8+param2)(A6),D1 ; get param2
unlk A6 ; unlink stackframe
rts
END
--snip--
A6 performs well sofar, however there is this offset of 8 bytes I don't like. For processing my stack parameters I won't need the old A6 value nor the return address of the routine call.
I tried doing LINK A6,#8 but this didn't gave me the right offset. Did I miss something?
All I want is to have A6 pointing at my call stack parameters without offset.
E.q. move.w 0(A6),D0 should load my first wordsized parameter into D0 instead of the current 8(A6).
Any ideas for this?
cheers,
ssb
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