Alien Rain into files (intact)

[Hot Rod <hotrod.apple2@gmail.com>]

I spotted a .nib of Alien Rain (fine Galaxian type game from Tony Suzuki/Broderbund), and since it had the original title screen and all, I thought a file version in normal format might be handy.

The protection was format-based, with track zero being a fairly normal 13-sector track, and tracks 1 through D also being 13 sector format, but with modified address markers.

Boot stage 0 and 1 loaded RWTS from track 0 into $B700-$BFFF.

The code starting at $B700 loaded the title screen stuff into $2000-$60FF from track 1 sector 0 through track 5 sector C, and then called the title screen routine at $6000.  

After returning, it then continued by loading the game into $1000-$77FF from track 6 sector 0 through track D sector C, calling the game start at $7600 (which in turn just has a small loop to wipe out part of the RWTS to cover its tracks and then jump to the real beginning at $1000).

The one interesting thing about the RWTS is that each track has its own address marker.  There's a lookup table tucked away at $400 on the text screen that's used to retrieve the second byte of the address marker and modify the RWTS code with it (e.g., instead of a normal D5 AA B5 for 13-sector format, look up and modify the marker to be D5 BE B5 for track 1).

And then before reading the second batch of tracks, the title screen code modified the RWTS to use DE instead of D5, but the other modification per track still was used too (so instead of D5 xx B5, the second batch used DE xx B5).

All this stuff is already preserved in the .nib, so rather than just converting/normalizing that to 16 sectors, single it's a single load game (beyond the title screen), I opted to just save out the title screen code and the game code as two separate pieces (using the game to load each piece to capture).

Then I just created a lazy BASIC program to run the title followed by the game.

It would probably be a good candidate to stitch together into one file, with compression and such, but I'll leave that to others who like to do that.

Image is sitting in Asimov incoming at the moment.

]HR