DeskTop diassembly notes

DESKTOP.SYSTEM

A short (8k) loader program. This is likely responsible for copying the rest to a RAM card (if available), then invoking the main app.

DESKTOP2.$F1

This is large - 111k. It includes a loader, the DeskTop app (with both main memory and aux memory segments, filling everything from $4000 to $FFFF (except for I/O space and ProDOS), and still having more code - probably the disk copy code which is swapped in dynamically.

The file is broken down into multiple segments:

segment 0: load - address $2000-$257F, length $0580, file offset $000000 (Loader)
segment 1: aux1 - address $4000-$BFFF, length $8000, file offset $000580 (A2D, part of DeskTop)
segment 2: aux2 - address $D000-$ECFF, length $1D00, file offset $008580 (More of DeskTop)
segment 3: aux3 - address $FB00-$FFFF, length $0500, file offset $00A280 (More of DeskTop)
segment 4: main - address $4000-$BEFF, length $7F00, file offset $00A780 (More of DeskTop)
segment 5: main - address $0800-$0FFF, length $0800, file offset $012680 (???)
segment 6: main - address $0290-$03EF, length $0160, file offset $012E80 (Invoker)
segment N: TBD - 38k so must be further subdivided. Disk Copy???

Structure

Loader

loader.s

Invoked at $2000; patches the ProDOS QUIT routine (at LC2 $D100) then invokes it. That gets copied to $1000-$11FF and run by ProDOS.

The invoked code stashes the current prefix and re-patches ProDOS with itself. It then (in a convoluted way) loads in the second $200 bytes of DESKTOP2 at $2000 and invokes that.

This code then loads the rest of the file as a sequence of segments, moving them to the appropriate destination in aux/banked/main memory.

There's fourth chunk of code; it's unclear where that ends up or how it is invoked, but it appears to handle an OpenApple+ClosedApple+P key sequence and invoke slot one code - possibly debugging support?

Invoker

s6.s

Loaded at $290-$03EF, this small routine is used to invoke a target, e.g. a double-clicked file. System files are loaded/run at $2000, binary files at the location specified by their aux type, and BASIC files loaded by searching for BASIC.SYSTEM and running it with the pathname passed at $2006 (see ProDOS TLM).

GUI Library "A2D"

a2d.s

AUX $4000-$8DFF is the GUI library used for the DeskTop application and (presumably) for disk copy and Selector apps (TBD).

Entry point is $4000 with a ProDOS MLI-style calling convention

Font is at $8800
Part of $8500-$87FF looks like part of "DeskTop" (see below), dealing with online volumes.

"DeskTop" Application

desktop.s

DeskTop application code is in the lower 48k of both Aux and Main:

Aux $8E00-$BFFF - sitting above the GUI library
Main $4000-$BEFF

...and in the Aux language card area (accessible from both aux and main code) are relays, buffers and resources:

Aux $D000-$ECFF - relays and other aux/main helpers, resources (menus, strings, window)
Aux $ED00-$FAFF - hole for data buffer
Aux $FB00-$FFFF - more resources (file types, icons)

($C000-$CFFF is reserved for I/O, and main $BF page and language card is ProDOS)

       Main              Aux               ROM
$FFFF +------------+    +------------+    +------------+
      | ProDOS     |    | DeskTop    |    | Monitor    |
$F800 |            |    | Resources/ |    +------------+
      |            |    | Buffers    |    | Applesoft  |
      |            |    |            |    |            |
      |            |    |            |    |            |
      |            |    |            |    |            |
$D000 +------------+    +------------+    +------------+    +------------+
                                                            | I/O        |
                                                            |            |
$C000 +------------+    +------------+                      +------------+
      | ProDOS     |    | DeskTop    |
$BF00 +------------+    | App Code   |
      | DeskTop    |    |            |
      | App Code   |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
$8E00 |            |    +------------+
      |            |    | A2D GUI    |
      |            |    | Library    |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
$4000 +------------+    +------------+
      | Graphics   |    | Graphics   |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
      |            |    |            |
$2000 +------------+    +------------+
      | Init &     |    | Desk Acc   |
      | Desk Acc   |    |            |
      |            |    |            |
$0800 +------------+    +------------+
      | Text       |    | Text       |
$0400 +------------+    +------------+
      | Invoker    |    |            |
$0300 +------------+    +------------+
      | Input Buf  |    | Input Buf  |
$0200 +------------+    +------------+
      | Stack      |    | Stack      |
$0100 +------------+    +------------+
      | Zero Page  |    | Zero Page  |
$0000 +------------+    +------------+

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