Re: A89: Re: porting Z80 to 68k.....possible?? (yes, but not easy)

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Re: A89: Re: porting Z80 to 68k.....possible?? (yes, but not easy)


I am probably the only person who writes z80 that uses the .db with
self-modifying code, so I wouldn't worry about it. Most people would do
it the way you mentioned for various benifits that I see, but I like
having the label right on the value... so I will just have to change

Patrick Davidson wrote:
> 
> > I have only 3 points to make:
> >
> > 1) What about a routine like this to access data?
> >    ld a,(level)
> >    ld b,a
> >    ld de,49 ;Size of a level
> >    ld hl,levelSet+1-49 ;levelSet-48
> > lvlAddLoop:
> >    add hl,de
> >    djnz lvlAddLoop
> > 49 is a odd number... and this is a program that will eventually be on
> > 83s
> 
> It depends on what's in the level data.  If it consists of only data,
> there will be no problem.  After all, all data is accessed as bytes by
> the Z80; there are no instructions to load a word from a variable
> address.  If you store this address in a word load instruction by
> self-modifying code, that will also still be OK since the word loads
> are split to avoid this problem.
> 
> > 2) What about people who write self-modifying code like this:
> >    .db $FE; cp n
> > levelCountCheck .db 0
> 
> That wouldn't work under the current design.  If it's only used in a
> few places, it's probably easier to just change the source code so it
> will work under the converter.  However, if I see a lot of this I may
> need to come up with a solution; this will be harder than the other
> way, since it's harder to determine what is or isn't code.
> 
> This way of writing self-modifying code is, however, much less logical
> than the one I mentioned.
> 
> > 3) What about actual data that is accessed by (label+1)?
> 
> That isn't a problem.  The self-modifying code conversion would only
> be done when there is code at label+1.  Of course, as you mentioned
> before, there are problems if the person enters code with .db
> directives.

-- 
Scott "_Wrath_" Dial
wrath@calc.org
ICQ#3608935
TimeCity AI Guy II - www.timecity.org
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