Thanks to Eckhard for the diagnosis and suggestions.
I've just posted (http://www.atari2600.org/dasm) an update to the VCS.H
file/package which incorporates a new label (TIA_BASE_ADDRESS) which is used
for generation of the TIA addresses. Normally, you don't worry about it -
TIA addresses now start at 0 - but if you want to do 3F-bankswitching,
define the constant with a value of $40, and that's your TIA base.
It's done using uninitialised segments, which gives cleaner code than adding
the base address to each hardware register.
The label can be defined as Eckhard suggests, or (what I do)
include -DTIA_BASE_ADDRESS=$40 in the assemble command-line when building
the code.
Cheers
A
----- Original Message -----
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
To: <stella@xxxxxxxxxxx>
Sent: Saturday, March 22, 2003 8:25 AM
Subject: Re: [stella] DASM 'upgrade' in progress
> >>
> Any reasons, why the TIA constants start at offset $40?
>
> AFAIK in all disassembled old games the registers start at $00.
>
> Or is it just to make disassembling with DiStella a bit more compliated?
> <<
>
> Andrew is working on a game with Tigervision's 3F bankswitching,
> where all accesses to addresses $3F and below will trigger the
> bankswitching logic. Therefore it is nessessary to to use the
> TIA mirror from $40 up.
>
> When I sent this file to Andrew I called it VCS3F.H to differentiate
> it from the normal VCS.H file. But maybe we should merge both files
> and add either $00 or $40 to the TIA equates depending on a defined
> constant? So the VCS.H file would look something like this:
>
> IFNCONST TIAOFFSET
> TIAOFFSET equ $00
> ENDIF
>
> VSYNC equ $00+TIAOFFSET
> VBLANK equ $01+TIAOFFSET
> etc.
>
> That way you could do a "TIAOFFSET equ $40" before you include the
> VCS.H file when you want to write a 3F bankswitched game. If you
> don't define that value it will default to $00 and all TIA addresses
> will be normal.
>
>
> Ciao, Eckhard Stolberg
>
>
> --------------------------------------------------------------------------
--------------------
> Archives (includes files) at http://www.biglist.com/lists/stella/archives/
> Unsub & more at http://www.biglist.com/lists/stella/
>
>
>
----------------------------------------------------------------------------------------------
Archives (includes files) at http://www.biglist.com/lists/stella/archives/
Unsub & more at http://www.biglist.com/lists/stella/
