This is an complete*, annotated disassembly of the prototype BIOS cartridge for the unreleased SFX-100 "Nintendo Playstation" console or SNES CD-ROM add-on. All* variables have been identified, as have data areas which have been reverse engineered into a (more) readable format (with the exception of graphics characters/tiles which are left in text format). Effort has been taken to remove many "magic" numbers and replace these with constants to aid readability.
The code is in such a state that it may be reassembled; not only to recreate the original ROM image, but also to include alterations and fixes, apply language translations, and to remove what looks to be unused cruft. It may not be the original source code, but it's plenty close enough for development purposes.
* Such absolute terms are of course difficult to defend. There could always be more lurking in the areas which look like padding and noise. Suffice it to say that the disassembly is self-consistent and there are no** unknown references in the code.
** Also to be taken with a pinch of salt...
If your build environment is set up correctly, simply issue the make command
to assemble and link the BIOS. The code uses a fair few directives specific to
the WLA-DX 65816 assembler, so expect to
have to make changes if using anything else.
Use the config.inc file to configure the build, for example to include fixes
or apply a language translation.
The following fixes may be enabled by building without ORIGINAL defined.
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Running the "SELF CHECK" procedure more than once would cause this to hang at the sound check phase. This was caused by trying to program the APU after it has already been programmed, so the APU never entered the "ready" state. The fix checks for the "programmed" state and skips trying to program the APU on subsequent runs.
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The procedure used to lock the SRAM during/after running diagnostics was different to that of the main program. The former has now been changed to match the latter.
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The "BACKUP RAM" menu had a subtle graphical glitch resulting in the last tile in the set having an incorrect background colour. This was due to a few missing words at the end of the encoded tile data, so the appropriate title screen tiles were not fully overwritten. These missing words have been added.
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When saving a new file to SRAM, the number of files was not checked against the allowed maximum. This check was however unnecessarily performed when overwriting an existing file. The check is now only done when saving a new file.
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Having zero files as well as zero free space was originally permitted. This causes problems if the whole SRAM is zeroed out; it makes it impossible to create new files, as the program incorrectly concludes there is not enough free space. Now, if both the number of files and free space are zero, this is treated as an error and the SRAM is re-initialised to a valid state.
Check the i18n directory for examples. New translations can best be added by
copying an existing file and editing as necessary, then defining LANG in
config.inc. Note that all macros must be defined and some things must have a
specific length for the translation to assemble correctly.
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Martin "Nocash" Korth's "fullsnes" documentation on both the SNES and the SFX-100 prototype was invaluable to this project.
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Alex "Dotsarecool" Losego's nifty graphical disassembler DiztinGUIsh was used for the initial disassembly and rough labeling.
Of course, this disassembly will by its very nature allow the recreation of what remains a copyrighted program; strings in the code even attest to the original copyright holder. One may argue that the ROM image is trivially accessible online via a cursory search, has been abandoned by its original author, has little to no commercial value and ultimately serves very little purpose.
In any case, the "author" (for as far as the creator of this disassembly can be termed as such) does not condone software piracy nor copyright infringement and presents this code solely for the purposes of study and the historical preservation of the knowledge found within.
No claims are made to copyright of the original code/image nor the disassembly, annotations and other derived works which may be considered to be in the public domain, as far as this is possible. The program is provided "as-is" without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose.