a2d/desktop

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. The second half is used to "Down load", i.e. copy Selector entries to RAMCard on first boot.

The file is present in the original distribution as DESKTOP1 but is renamed DESKTOP.SYSTEM in many disk images to be launched at boot.

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:

Purpose	File Offset	Bank	Address	Length	Sources
Loader	B$000000	Main	A$2000-$257F	L$0580	loader.s
MGTK/DeskTop	B$000580	Aux	A$4000-$BFFF	L$8000	mgtk.s, desktop_aux.s
DeskTop	B$008580	Aux LC	A$D000-$ECFF	L$1D00	desktop_res.s
DeskTop	B$00A280	Aux LC	A$FB00-$FFFF	L$0500	desktop_res.s
DeskTop	B$00A780	Main	A$4000-$BEFF	L$7F00	desktop_main.s
Initializer	B$012680	Main	A$0800-$0FFF	L$0800	desktop_main.s
Invoker	B$012E80	Main	A$0290-$03EF	L$0160	invoker.s
Disk Copy 1/4	B$012FE0	Main	A$0800-$09FF	L$0200	ovl1.s
Disk Copy 2/4	B$0131E0	Main	A$1800-$19FF	L$0200	ovl1a.s
Disk Copy 3/4	B$0133E0	Aux LC	A$D000-$F1FF	L$2200	ovl1b.s
Disk Copy 4/4	B$0155E0	Main	A$0800-$12FF	L$0B00	ovl1c.s
Format/Erase	B$0160E0	Main	A$0800-$1BFF	L$1400	ovl2.s
Selector 1/2	B$0174E0	Main	A$9000-$9FFF	L$1000	ovl3.s
Common	B$0184E0	Main	A$5000-$6FFF	L$2000	ovl4.s
File Copy	B$01A4E0	Main	A$7000-$77FF	L$0800	ovl5.s
File Delete	B$01ACE0	Main	A$7000-$77FF	L$0800	ovl6.s
Selector 2/2	B$01B4E0	Main	A$7000-$77FF	L$0800	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_main.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 which includes in:

• desktop_aux.s
• desktop_lc.s (which pulls in desktop_res.s)
• desktop_main.s

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

• Aux $851F-$BFFF - sitting above the GUI library (desktop_aux.s)
• Main $4000-$BEFF (desktop_main.s)

...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)

desktop_res.s defines these common resources. It is built as part of desktop.s. Early in the build process it is also built as part of desktop_res_build.s which is processed to produce out/desktop_res.inc, which is used by the overlay sources.

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 +-------------+    +-------------+
      | Drawing     |    | Drawing     |
      | Temp Buffer |    | Temp Buffer |
$0400 +-------------+    +-------------+
      | Invoker     |    |             |
$0300 +-------------+    +-------------+
      | Input Buf   |    | Input Buf   |
$0200 +-------------+    +-------------+
      | Stack       |    | Stack       |
$0100 +-------------+    +-------------+
      | Zero Page   |    | Zero Page   |
$0000 +-------------+    +-------------+

Disk Copy Overlay

The Disk Copy command replaces large chunks of memory and is best thought of as a separate application.

The first part (ovl1.s) loads into main memory the other overlays, but in turn it loads a second short ($200-byte) overlay (ovl1a.s). This then loads a replacement for the resources in the aux language card area (ovl1b.s) and another block of code in main memory (ovl1c.s). When exiting, the DeskTop is restarted from the beginning.