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ProSel-8 Utility Disassembly

Glen Bredon wrote several Apple II utilities, including the Merlin assembler, DOS Master, ProSel-8, and ProSel-16.

ProSel-8 does some fairly complex shuffling when it starts up, so I did a quick disassembly to evaluate the updated address region code in SourceGen v1.8. I haven't done much in terms of explaining what the bulk of the code does, but it's a good starting point for anybody who wants to dig in. This is not a finished disassembly.

The code uses inline data for ProDOS-8 calls, SmartPort calls, and string formatting (high-ASCII null-terminated strings with embedded HTAB values). The latter is likely common to the various ProSel-8 utilities, so I wrote a script to handle it.

ProSel-8 is copyright 1990 Glen Bredon.

CAT.DOCTOR / CD.EXT memory map

The Cat.Doctor.Combo data file is a concatentation of CAT.DOCTOR and CD.EXT. The former is the executable, the latter is a code overlay loaded by the main program when it first launches. Calls are made in both directions, so it's easiest to work with them in a single binary.

If CD.EXT can't be loaded, or auxillary memory isn't available, the features implemented by it aren't available from the menu.

Here's a summary of how the file is laid out in memory:

+000000  +- start
+000000  | +- start
         | |  $2000 - $2002  length=3 ($0003)
+000003  | | +- start 'LBE80'  pre='src_2003'
         | | |  $be80 - $beff  length=128 ($0080)
+000082  | | +- end
         | | 
         | |  $2083 - $21a7  length=293 ($0125)
+0001a8  | | +- start 'LBD00'  pre='src_21a8'
         | | |  $bd00 - $bd16  length=23 ($0017)
+0001be  | | +- end
         | | 
         | |  $21bf - $2226  length=104 ($0068)
+000226  | +- end
+000227  | +- start 'MainEntry'  pre='src_2227'
         | |  $0800 - $2f75  length=10102 ($2776)
+00299c  | +- end
+00299d  | +- start 'LBE00'  pre='src_499d'
         | |  $be00 - $be7d  length=126 ($007e)
+002a1a  | +- end
+002a1b  | +- start 'LD000'  pre='src_4a1b'
         | |  $d000 - $d0fd  length=254 ($00fe)
+002b18  | +- end
+002b19  | +- start 'unref_d400?'  pre='src_4b19'
         | |  $d400 - $ddf5  length=2550 ($09f6)
+00350e  | +- end
+00350e  +- end

+00350f  +- start 'L4000'
         |  $4000 - $52ff  length=4864 ($1300)
+00480e  +- end

The map is complicated slightly by the JMP $2083 at the very start, because $2083 appears in two different places: the initialization code, and the relocated main program. The intended target is at +000083 in the init code, but if you just establish a simple list of address regions you create an ambiguous situation. The address at +001aaa is also a viable candidate, so whether or not the disassembly comes out as desired depends on the resolution algorithm.

The ambiguity was resolved here by wrapping the initialization code in a separate address region, from +000000 to +000226. This ensures that the JMP is resolved to the nearby instance.

It looks a little weird in the source file to have two .addrs $2000 pseudo-ops right next to each other. The one that spans the entire CAT.DOCTOR binary is required, though, because we need to establish addresses for the pre-labels. For example, src_499d is at address $499d before the code is relocated, but we wouldn't know that without establishing that the file started at $2000.

Copyright 2021 by Andy McFadden