# 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. NOTE: The second half may be used for "Down load", i.e. copy Selector entries to RAMCard as well. ## 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](../MGTK.md) - 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 +-------------+ +-------------+ | Drawing | | Drawing | | Temp Buffer | | Temp Buffer | $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.