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# 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
segments swapped in dynamically.
The file is broken down into multiple segments:
* segment 0: load - A$2000-$257F, L$0580, mark $000000 (Loader)
* segment 1: aux - A$4000-$BFFF, L$8000, mark $000580 (A2D, DeskTop)
* segment 2: auxlc - A$D000-$ECFF, L$1D00, mark $008580 (DeskTop)
* segment 3: auxlc - A$FB00-$FFFF, L$0500, mark $00A280 (DeskTop)
* segment 4: main - A$4000-$BEFF, L$7F00, mark $00A780 (DeskTop)
* segment 5: main - A$0800-$0FFF, L$0800, mark $012680 (Initializer)
* segment 6: main - A$0290-$03EF, L$0160, mark $012E80 (Invoker)
* segments dynamically loaded for these actions:
* disk copy - A$0800, L$0200, mark $012FE0
* format/erase - A$0800, L$1400, mark $0160E0
* selector - A$9000, L$1000, mark $0174E0
* common - A$5000, L$2000, mark $0184E0 (used by selector, copy, delete)
* file copy - A$7000, L$0800, mark $01A4E0
* file delete - A$7000, L$0800, mark $01ACE0
* selector - A$7000, L$0800, mark $01B4E0
* (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
`desktop.s`
Loaded at $800-$FFF, this does one-time initialization of the
DeskTop. It is later overwritten when any desk accessories are
run.
### GUI Library "A2D"
`a2d.s`
AUX $4000-$851E 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
### "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
* Aux $FB00-$FFFF - more resources (file types, icons)
($C000-$CFFF is reserved for I/O, and main $BF page and language card is ProDOS)
Interactive commands including disk copy/format/erase, file
copy/delete, and Selector add/edit/delete/run all dynamically load
main memory code segments into one or more of: $800-$1FFF,
$5000-$6FFF, $7000-$77FF, and $9000-$9FFF. When complete, any original
code above $4000 is reloaded.
```
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 | +------+ | |
| | Seg | | |
| | | | |
| | | | |
$9000 | +------+ | |
| | | |
$8800 | | | Font |
| | | |
$851F | | +-------------+
| | | A2D GUI |
| | | Library |
| | | |
| | | |
$7800 | +------+ | |
| | Seg | | |
$7000 | +------+ | |
| | Seg | | |
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
$5000 | +------+ | |
| | | |
| | | |
| | | |
| | | |
$4000 +-------------+ +-------------+
| Graphics | | Graphics |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
$2000 +-------------+ +-------------+
| Initializer | | Desk Acc |
| & Desk Acc | | |
| & Segments | | |
| | | |
$0800 +-------------+ +-------------+
| Text | | Text |
| | | |
$0400 +-------------+ +-------------+
| Invoker | | |
$0300 +-------------+ +-------------+
| Input Buf | | Input Buf |
$0200 +-------------+ +-------------+
| Stack | | Stack |
$0100 +-------------+ +-------------+
| Zero Page | | Zero Page |
$0000 +-------------+ +-------------+
```
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