libretro-atari800/atari800/DOC/BUGS

Bugs and Known Problems
-----------------------

* Cosmic Balance (game) hangs before the intro screen. This is probably
  due to inaccurate emulation of POKEY interrupts (see below). The program 
  uses a hardware SIO loader as part of a presumed protection scheme.  
  There is a bug in the code which activates the POKEY timers at an 
  absurdly high frequency. This causes repeated interrupts which hangs the 
  program.
  Probably there is some interaction with SIO which prevents this on
  a real Atari.
  A workaround is to invoke the monitor and type "c 10 40" and "cont".

* new Pokey engine doesn't switch to mono output in STEREO_SOUND config

* new Pokey engine doesn't support VOL_ONLY_SOUND on the second Pokey

* a few keyboard-related bugs: e.g. pressing SHIFT+1 and then
  releasing SHIFT should still give '!' characters

* The cycle-exact ANTIC/GTIA/CPU timing is not 100%.
  This causes display bugs in following programs:
  - Surf's up (game) (the horizon)
  - Satan's Hollow (game) (horizon) (confirmed sta WSYNC at WSYNC_C bug)
  - Dimension X (game) (alignment problem)
  - Te.mod (demo) (small glitched pixel in the final credits on the bottom left)
  - Our 5oft Unity Part (demo) (cycle-alignment, probably WSYNC)
  - Isolation (demo) (vector animations)
  - 80 Random Moving Rectangles (demo) (top left of rectangles, screen data
    is modified while drawing a scanline)
  - Sirius games: Scores and Text in Worm War I, Final Orbit, Spider City, 
    Turmoil, Fantastic Voyage.  These games store screen data in page 0
    and modify it each scan line.  They reuse the same data for each
    scan line with an LMS on every line.  This makes the code look 
    like 2600 code. Emulating this requires trapping writes to
    page 0 and doing partial ANTIC loads. 
  - Spider City has another bug in the map which is caused by player graphics
    and HPOS being changed before the player is finished being drawn.  This
    is only possible for wide players. 
  - Extract (demo) (face)

* Non-bugs:
  - Ergo Bibamus (demo) (one pixel of the flower above the perspective scroll)
  - Mail Order Monsters (game)
    (some colour changes do not align with text, occurs on a real Atari)
  - The Break (demo) (bugs on the left side of photo)
  - Star Raiders (disk image) (game) (doesn't work on XL/XE, select OS/B)
  - Many other disk images of cartridges that work on XL/XE require OS B
    because a once-popular cart dumping program for the Atari 800 generates
    an OS B-specific loader. IIRC it loads the image and jumps into the OS B
    RESET vector location, which is changed on the XL.
  - Strip Poker (game) (Atari Basic must be enabled)
  - Joust (Atari 5200 game) (the game sets all colors to black on PAL systems,
    you need to switch the emulator to NTSC mode)

* The following programs are improved by using the new cycle-exact code:
  - 8 Players Demo (demo)
  - Bewesoft's Demo (demo)
  - Bitter Reality (demo)
  - Demonic Laughter (music collection)
  - Extract (graphics collection)
  - GED (graphics editor)
  - Joyride (demo)
  - Mail Order Monsters (game)
  - Master of the Lamps (game)
  - Orneta '95 invitro (demo)
  - Our 5oft Unity Part (demo)
  - Studio Dream (demo)
  - Sweet Illusion (demo)
  - Te.mod (demo)
  - The Break (demo)
  - Miner 2049'er (game) (rotating 5's)
  - Dimension X (game) (title screen upper and lower bars)
  - Graphics impossible (demo) (Antic magazine)
  - Power Graph (graphics editor)
  - Darkness Warrior (picture)

* POKEY interrupts are scanline-, not cycle-exact.
  This causes display or sound bugs in following programs:
  - Joyride (demo) (white lines on title picture)
  - Mirax Force (game) (speech)
  - Saturday Demo (demo) (music)
  - The Last Guardian (game) (speech)
  - Digital Trash (demo) (music)

* VOL_ONLY_SOUND causes sound bugs in following programs:
  - Ghostbusters (game)
  - Overmind (demo)

* intensive 130xe-banks switching slows down emulation much.
  This causes performance problems in following programs:
  - Impossible but Real (demo)
  - Sheol (demo)
  - Total Daze (demo)
  - Ultra (demo)

* The following VAPI images are known to not work:
  (This list may not be complete, as full VAPI documentation
   has never been released by the author)
  - Alternate Reality: The City
  - Ankh
  - Attack at EP CYG 4
  - Ballblazer Activision (UK)
  - Jenny of the Prairie
  - Mercenary - Escape from Targ _ Novagen Software
  - Mr. Do!
  - Music Studio (The)
  - Promoteur
  - Rescue on Fractalus! _ Activision (UK)
  - Spy vs Spy
  - Targets - A Number Game

* SDL port uses call back system for filling sound buffer.
  This causes wrong sound effects (noise) in some games.