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DeskTop diassembly notes

DESKTOP.SYSTEM

sys.s

A short (8k) loader program. This is 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 and 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 segments swapped in dynamically.

The file is broken down into multiple segments:

  • segment 0: load - A$2000-$257F, L$0580, B$000000 (loader.s; Loader)
  • segment 1: aux - A$4000-$BFFF, L$8000, B$000580 (mgtk.s, desktop.s; MGTK, DeskTop)
  • segment 2: auxlc - A$D000-$ECFF, L$1D00, B$008580 (desktop.s; DeskTop)
  • segment 3: auxlc - A$FB00-$FFFF, L$0500, B$00A280 (desktop.s; DeskTop)
  • segment 4: main - A$4000-$BEFF, L$7F00, B$00A780 (desktop.s; DeskTop)
  • segment 5: main - A$0800-$0FFF, L$0800, B$012680 (desktop.s; Initializer)
  • segment 6: main - A$0290-$03EF, L$0160, B$012E80 (invoker.s; Invoker)
  • overlays dynamically loaded for these actions:
    • disk copy - A$0800-$09FF, L$0200, B$012FE0 (ovl1.s)
      • which loads - A$1800-$19FF, L$0200, B$0131E0 (ovl1a.s)
      • which loads - A$D000-$F1FF, L$2200, B$0133E0 (ovl1b.s; overwrites the aux LC)
      • and... - A$0800-$12FF, L$0B00, B$0155E0 (ovl1c.s)
    • format/erase - A$0800-$1BFF, L$1400, B$0160E0 (ovl2.s)
    • selector - A$9000-$9FFF, L$1000, B$0174E0 (ovl3.s)
    • common - A$5000-$6FFF, L$2000, B$0184E0 (ovl4.s; used by selector, copy, delete)
    • file copy - A$7000-$77FF, L$0800, B$01A4E0 (ovl5.s)
    • file delete - A$7000-$77FF, L$0800, B$01ACE0 (ovl6.s)
    • selector - A$7000-$77FF, L$0800, B$01B4E0 (ovl7.s)
  • (EOF is $01BCE0)

The DeskTop segments loaded into the Aux bank switched ("language card") memory can be used from both main and aux, so contain relay routines, resources, and buffers. More details below.

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, which expects to live at $280 so it can't co-exist with the Invoker; it may be temporary code, as there is no sign that it is ever moved into place. It's also unclear how it would be hooked in. The routine detects OA+CA+P and prints the DHR screen to an ImageWriter II printer attached to Slot 1. (This may have been used to produce screenshots during development for manuals.)

Invoker

invoker.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).

Initializer

(in desktop.s)

Loaded at $800-$FFF, this does one-time initialization of the DeskTop. It is later overwritten when any desk accessories are run.

MouseGraphics ToolKit (MGTK)

mgtk.s

Aux $4000-$851E is the MouseGraphics ToolKit - a GUI library used for the DeskTop application.

Since this resides in Aux memory, DeskTop spends most of its time with Aux read/write enabled. The state and logic for rendering the desktop and window contents resides in Aux to avoid proxying data.

"DeskTop" Application

desktop.s

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

  • Aux $851F-$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 - entries for each icon on desktop/in windows
  • Aux $FB00-$FFFF - more resources (file types, icons)

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

Aux $1B00-$1F7F holds lists of icons, one for the desktop then one for up to 8 windows. First byte is a count, up to 127 icon entries. Icon numbers map indirectly into a table at $ED00 that holds the type, coordinates, etc. Aux $1F80-$1FFF is a map of used/free icon numbers, as they are reassigned as windows are opened and closed.

Overlays

ovl1.s etc

Interactive commands including disk copy/format/erase, file copy/delete, and Selector add/edit/delete/run all dynamically load main memory code overlays into one or more of: $800-$1BFF, $5000-$6FFF, $7000-$77FF, and $9000-$9FFF. When complete, any original code above $4000 is reloaded.

Memory Map

       Main               Aux                 ROM
$FFFF +-------------+    +-------------+    +-------------+
      | ProDOS      |    | DeskTop     |    | Monitor     |
$F800 |             |    | Resources/  |    +-------------+
      |             |    | Buffers     |    | Applesoft   |
      |             |    |             |    |             |
      |             |    |             |    |             |
      |             |    |             |    |             |
$D000 +-------------+    +-------------+    +-------------+    +-------------+
                                                               | I/O         |
                                                               |             |
$C000 +-------------+    +-------------+                       +-------------+
      | ProDOS GP   |    | DeskTop     |
$BF00 +-------------+    | App Code    |
      | DeskTop     |    |             |
      | App Code    |    |             |
      |             |    |             |
      |             |    |             |
      |             |    |             |
      |             |    |             |
$A000 |      +------+    |             |
      |      | Ovl  |    |             |
      |      |      |    |             |
      |      |      |    |             |
$9000 |      +------+    |             |
      |             |    |             |
$8E00 |             |    | Entry Point |
      |             |    |             |
$8800 |             |    | Font        |
      |             |    |             |
$851F |             |    +-------------+
      |             |    | MGTK        |
      |             |    |             |
      |             |    |             |
      |             |    |             |
$7800 |      +------+    |             |
      |      | Ovl  |    |             |
$7000 |      +------+    |             |
      |      | Ovl  |    |             |
      |      |      |    |             |
      |      |      |    |             |
      |      |      |    |             |
      |      |      |    |             |
      |      |      |    |             |
      |      |      |    |             |
      |      |      |    |             |
$5000 |      +------+    |             |
      |             |    |             |
      |             |    |             |
      |             |    |             |
      |             |    |             |
$4000 +-------------+    +-------------+
      | Graphics    |    | Graphics    |
      |             |    |             |
      |             |    |             |
      |             |    |             |
      |             |    |             |
      |             |    |             |
      |             |    |             |
      |             |    |             |
$2000 +-------------+    +-------------+
      | Initializer |    | Win/Icn Map |
$1B00 | & Desk Acc  |    +-------------+
      | & Overlays  |    | Desk Acc &  |
      |             |    | Save Area   |
      |             |    |             |
$0800 +-------------+    +-------------+
      | Text        |    | Text        |
      |             |    |             |
$0400 +-------------+    +-------------+
      | Invoker     |    |             |
$0300 +-------------+    +-------------+
      | Input Buf   |    | Input Buf   |
$0200 +-------------+    +-------------+
      | Stack       |    | Stack       |
$0100 +-------------+    +-------------+
      | Zero Page   |    | Zero Page   |
$0000 +-------------+    +-------------+

The Disk Copy command replaces large chunks of memory and is best thought of as a separate application. When exiting, the DeskTop is restarted from the beginning.