Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!agate!ig!uwmcsd1!lakesys!jason
From: jason@lakesys.UUCP (Jason)
Newsgroups: comp.sys.apple
Subject: Re: 65816 Move Bytes Instruction
Summary: MVN Stuff
Message-ID: <908@lakesys.UUCP>
Date: 28 Jul 88 15:38:36 GMT
References: <6230014@hpindda.HP.COM>
Organization: Lake Systems, Milwaukee Wisconsin
Lines: 25

In article <6230014@hpindda.HP.COM>, tribby@hpindda.HP.COM (David Tribby) writes:
> [...] via the MVN instruction. Everything was fine
> as long as the global block and code segment were in the same data bank.
> But last night my program must have grown over the boundary. When the
> MVN instruction executed, it set the Data Bank Register (B-reg) to the
> bank containing the subroutine. When the subroutine returned to Pascal,
> the B-reg pointed to the wrong area...and all sorts of strange things
> happened! I fixed the problem by saving the B-reg upon entering the
> subroutine and restoring it before returning.
> 
> --Dave Tribby

	Upon exit, the MVN or MVP instructions leave the DBR containing the
bank specified as the target bank. I suppose it might be useful in some cases,
but it sure seems like a pain to me - I use PHB & PLB as well (seems to be the
only easy way... not like it takes up tons of code space).

	As far as doing "variable" moves, I think that the self-modifying code
is the only possible trick... It seemed sort of annoying to me, but then I
thought about how the parameters would be passed (Considering that the A,X,
and Y regs are all used), and figured I'd just count my blessings... 7 cycles
per byte ain't too bad!

-- 

Jason - Not your average iconoclast  |	UUCP: uwvax!uwmcsd1!lakesys!jason