Date : Sat, 04 Mar 2006 09:07:23 +0000 (GMT)
From : BBC Micro <b_b_c_m_i_c_r_o@...>
Subject: Disassembling Castle Quest, SWOOP etc etc - RE: Re: SHELIA and the VIA's
Hi, good question, I used this:-
http://freshmeat.net/projects/6502dis/?branch_id=43939&release_id=150411
Although I had to modify it to compile it in MS VC++
because of some of the headers it was including.
6502dis is nice because you can modify the source code
to suit your needs.
This guy has got some disassemblies (bottom of his
page), SWOOP, SIEGE, GRABBIT etc... nicely commented:-
http://home.freeuk.com/c.r.dewhurst/bbc/
Its also interesting to look at the illegal techniques
they've used, like &fe79 and reading &ec for the
keypreses.
Next thing in CastleQ is I need to get to grip with
the graphics to find the sprites and their handling. I
had the ambitious plan to rewrite it for the PC/Linux
and maybe learn a few things on the way.(Three birds
with one stone!) A bit ambitious maybe.
Two useful books(read them yesterday) have been the
"Advanced Machine Code Techniques" and "How to Write
Arcade Games".
Regards,
Mark
--- Helen & John Simpson
<helenandjohn.simpson@...> wrote:
> Hi Mark
>
> I've tried disassembling some games myself (not
> Castle Quest though) and
> like you I found it an interesting distraction to
> pass the time on long
> train journeys!
>
> How good is this disassembler 6502dis that you have
> used? I couldn't
> find anything adequate so I wrote my own
> disassembler in BBC Basic V. It
> is quite rough but it works well.
>
> I'll have a detailed look at your pages if I get
> time.
>
> Cheers
> john
>
> > -----Original Message-----
> > From: Majordomo List Manager
> [mailto:majordomo@...]
> > On Behalf Of BBC Micro
> > Sent: 02 March 2006 18:21
> > To: bbc
> > Subject: Re: [BBC-Micro] Re: SHELIA and the VIA's
> >
> >
> > Thanks Jonathan and others, a useful list in that
> > link...
> >
> > Its quite interesting dissasembling, a bit like a
> > crossword, to begin with, I'll see how far I get
> > before it gets too difficult. I put up the page of
> the
> > main body of code:-
> >
> >
>
http://whitebody.tripod.com/castlequest/quest1_1528.htm
> >
> > and created a quick and dirty page with links to
> other
> > fragments:-
> >
> > http://whitebody.tripod.com/castlequest/
> >
> > Mark
> >
> >
> > --- Jonathan Graham Harston
> <jgh@...>
> > wrote:
> >
> > > > Message-ID:
> > >
> >
>
<20060227185954.6030.qmail@...>
> > >
> > > BBC Micro <b_b_c_m_i_c_r_o@...> wrote:
> > > > confused...Page 397 tells us that the VIAs are
> > > > &FE40-&FE7F. The next chapter tells us that
> VIA-B
> > > is
> > > > &FE60-&FE6F.
> > >
> > > Correct. The VIAs are at &FE40-&FE7F. The System
> VIA
> > > is at
> > > &FE40-&FE5F and the User VIA is at &FE60-&FE7F.
> > > There are sixteen
> > > registers in each VIA, so their defined
> locations at
> > > &FE40+x and
> > > &FE60+x
> > >
> > > > I'm having trouble tying up the memory
> locations
> > > with
> > > > the registers/ports on the VIA can anyone give
> a
> > > list
> > > > from &FE40-&FE7F? I only found the Electron
> one on
> > > the
> > > > internet search.
> > >
> > >
> http://mdfs.net/Docs/Comp/BBC/Hardware/SHEILAddrs
> > >
> > > > I've dissasembled Castle Quest (with 6502dis)
> and
> > > > looking at the VIA calls. &FE79?
> Joystick/Timer?
> > >
> > > &FE79 is a reflection of &FE69. It happens
> because
> > > only address
> > > lines A5-A7 are decoded, so &FE60 is repeated at
> > > &FE70. Similarly,
> > > the CRTC is repeated all along &FE00-&FE07.
> > >
> > > You should never use or depend on accessing
> anything
> > > at a
> > > reflection address.
> > >
> > > > This was the one of the pieces of code:-
> > > >
> > > > $2cfc: a5 32 LDA $32
> > > > $2cfe: 38 SEC
> > > > $2cff: ed 79 fe SBC $fe79
> > >
> > > They are being naughty. They should have used
> $fe69.
> > > That code has
> > > no guarrantee of working on any hardware that
> may
> > > fully decode the
> > > address of the VIA.
> > >
> > > --
> > > J.G.Harston - jgh@... -
> > > mdfs.net/User/JGH
> > > RISC OS Internationalisation -
> > > http://mdfs.net/Software/RISCOS
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