Challenger ROM disassembly

The Opus Challenger 3-in-1 was a combined disc interface, disc drive and RAM disc for the BBC Micro.

This repo exists to provide a disassembly of the Challenger 2.00 ROM, the last ROM made for it, and to provide a patched version suitable for use with a BBC B (since as supplied it effectively only works on the BBC Master).

The current disassembly is the raw output from da65, with meaningful labels and (hopefully) most of the code and data separated out. Once I'm happy this bit all makes sense, I'll probably start working on it by hand, making it 64tass-friendly, adding comments, adding appropriate org directives for the NMI routines, turning absolute addresses into label-relative offsets when necessary, adding < and > operators where appropriate, and so on...

Challenger info

Pics and stuff: http://chrisacorns.computinghistory.org.uk/8bit_Upgrades/Opus_Challenger3.html, http://www.beebmaster.co.uk/8bit/Challenger.html

Some tech info: http://modelb.bbcmicro.com/tech-challenger.html

Stardot thread about Challenger 2.00, with Master 128-only ADFS support: https://stardot.org.uk/forums/viewtopic.php?f=32&t=11795&hilit=challenger+adfs&start=30

Patched 2.00 ROM

The Challenger 2.00 DFS ROM sort-of works on its own in a BBC B, but doesn't initialise properly without the ADFS ROM, effectively making it Master-only (and going by the code I actually suspect it wouldn't work on its own even then). The patched version fixes this. Full list of changes:

• initialise DFS properly on reset
• tidy up wonky *CAT output
• advertises itself as version 200B

The patched ROM image is in the repo as beeb/chaldis/1/R.PCH200.

Use at your own risk! - I do use this patched ROM in my BBC B myself, and no problems noted so far, but I don't store anything important on discs...

The patched ROM should work on the Master, with or without the ADFS part, but I haven't tested this yet.

Repo layout

101

Quick disassembly of the Challenger 1.01 ROM - see CH101_da65.asm. (There is a later 1.03 ROM, but 1.01 is the one that my BBC Micro happened to have, so I decided to go with that.)

Not sure how far I'm going to go with this - so far, it's for comparison to the 2.00 ROM only.

200

Disassembly of Challenger 2.00 ROM. The ROM is 32K, so it's in two parts - see CH200_da65.asm and CHADFS_da65.asm.

beeb

BeebLink volume holding some test programs and the patched 2.00 ROM for use with BBC B.

originals

Original ROMs, random Slogger advert pic, and anything else I find.

tools

Tools for use on PC. So far, just the ROM patcher that makes the BBC B version of Challenger 2.00.

Building

The build outputs are in the repo already, so you only need to do this if you're going to modify something...

Prerequisites:

• da65
• Python 2.x on PATH
• Perl 5.x on PATH
• Some kind of Unix with all the usual Unix stuff (I use Mac OS X)

The build process does the following:

• run da65 to generate initial Challenger 1.01 disassembly (outputs ./101/CH101_da65.asm)
• run da65 to generate initial Challenger 2.00 disassembly (outputs ./200/CH200_da65.asm and ./200/CHADFS_da65.asm)
• run Perl to paste Greg Cook's comments into the Challenger 2.00 disassembly
• run ./tools/patch_ch200.py to generate patched Challenger 2.00 ROM for use on BBC B (outputs ./beeb/chaldis/1/R.PCH200)

Type make to run it.

(Once I start hand-editing the disassembly, these build steps will become mostly redundant.)