
EMUfailure.txt

Uwe Bonnes (original author), bon@elektron.ikp.physik.th-darmstadt.de

   May 20, 2005 for dosemu 1.3.2 (and possibly earlier versions)

   This file lists programs and groups of programs not running or running
   only partially under dosemu. The most up-to-date version of this file
   may be found on: http://www.dosemu.org/. Please report about possible
   additions to linux-msdos@vger.kernel.org or the SourceForge BTS at
   http://www.dosemu.org/. Perhaps your program can be made going with
   the help of others. Have a look at the dosemu-howto how to do so.
     _________________________________________________________________

   Table of Contents
   1. Fundamental problems

        1.1. Virtual Control Program Interface (VCPI)
        1.2. Programs using older versions of the Pharlap Extender
        1.3. Programs using the JEMM memory manager
        1.4. Does my failing program belong to these groups?
        1.5. Fundamental problem with the Linux kernel
        1.6. Fundamental problems with the CPU

              1.6.1. Problem with the virtualization of the IF flag
              1.6.2. ESP register corruption

   2. Known bugs

        2.1. Things YOU may help changing

              2.1.1. List of currently known bugs in Dosemu 1.2.2.

   3. Programs exhibiting graphical problems in xdosemu

        3.1. Games with graphical problems

1. Fundamental problems

   Programs that don't work under the MSDOS Emulator and probably won't
   ever work, because of fundamental problems. Some of these fundamental
   problems result in these programs not being runnable on
   Win3.x/Win95/WinNT and under OS/2 DOS box either. These programs are
   characterized by using any of these features:
     _________________________________________________________________

1.1. Virtual Control Program Interface (VCPI)

   VCPI allows programs to run in ring 0. This is kernel mode in Linux
   and not sensible.

   Example: sim2181.exe from Analog Devices DSP Kit
     _________________________________________________________________

1.2. Programs using older versions of the Pharlap Extender

   Older versions of the Pharlap Extender (run286) need ring-0 access
   under DOSEMU to install their own DPMI server. The use of proprietary
   undocumented extensions to the DPMI protocol makes DOSEMU's DPMI
   server unsuitable for this extender.

   Example: Autocad Version 12c1 For DOS

   Example: the game BioForge by Origin Systems.
     _________________________________________________________________

1.3. Programs using the JEMM memory manager

   The JEMM memory manager provides proprietary extensions to the EMS
   protocol. These are not supported by DOSEMU.

   Example: Wing Commander Privateer by Origin Systems
     _________________________________________________________________

1.4. Does my failing program belong to these groups?

   Check with "strings <program.exe> | less" if the program contains some
   of these keywords: vcpi, RUN286.
     _________________________________________________________________

1.5. Fundamental problem with the Linux kernel

   The Programmable Interval Timer (PIT) can be programmed to produce
   interrupts with frequencies up to almost 2MHz. Linux sets this to only
   100Hz (2.6 kernels can set it to 1KHz) and doesn't allow the software
   to change that. This limits the minimal interval between subsequent
   SIGALRM notifications for software that uses the setitimer(2) syscall.
   To emulate the PIT frequencies that are higher than the frequency
   Linux sets the PIT to, dosemu uses "interrupt bursts": on every
   SIGALRM reception dosemu triggers the timer interrupt as many times as
   necessary to compensate the gap since the previous SIGALRM reception.
   This allows to keep a precise timing but causes problems for some
   programs. When the timer interrupt handler is invoked more than once
   without letting the main thread to execute, some programs can lock up.
   The game "Cosmo" is one of those.

   Another problem is that due to the aforementioned low timer frequency
   dosemu is not able to properly emulate the timings for different
   emulated hardware. That also causes problems for some programs. Scream
   Tracker 3, for example, can lock up at startup because the interrupt
   from an emulated SB card can be triggered earlier than it should be in
   a real system.

   Possibly a workaround may be found in future DOSEMU versions.
     _________________________________________________________________

1.6. Fundamental problems with the CPU

   There are several defects in Intel's x86 CPUs that are causing
   problems for some software. Below is a description of the defects that
   are known to cause problems for software running under dosemu.
     _________________________________________________________________

1.6.1. Problem with the virtualization of the IF flag

   Intel's manual
   http://www.intel.com/design/intarch/techinfo/pentium/inout.htm says:

   " A procedure may use the POPF instruction to change the setting of
   the IF flag only if the CPL is less than or equal to the current IOPL.
   An attempt by a less privileged procedure to change the IF flag does
   not result in an exception; the IF flag simply remains unchanged. "

   The fact that the exception is not being generated, prevents dosemu
   from catching and properly simulating the POPF instruction executed in
   protected mode. That, in particular, means that the following code,
   executed in protected mode (not in v86 mode) under dosemu, will end up
   with interrupts disabled (IF cleared):

    sti
    pushf
    cli
    popf

   [ the interrupts are still disabled here ]

   This bug can only affect DPMI programs, as using DPMI is the only way
   to execute protected mode code under dosemu. Known programs that are
   affected are the games from ID software, namely Doom2 and Duke Nukem
   3D, but only when configured with sound. An optional work-around was
   added to dosemu, which just re-enables the interrupts if they were
   disabled for too long in protected mode. Additionally the address of
   the instruction that disabled the interrupts, is added to a black-list
   and this instruction is ignored for subsequent passes so that it can't
   disable the interrupts any more. This is potentially unsafe, but if
   the timeout is long enough, no harm was observed so far. The timeout
   is configured via the $_cli_timeout option, which is measured in a
   10ms timer ticks. Setting that option to 0 disables the workaround
   completely, making Doom2 unplayable with sound enabled.
     _________________________________________________________________

1.6.2. ESP register corruption

   Intel's x86 CPUs have a defect described here:
   http://www.intel.com/design/intarch/specupdt/27287402.PDF chapter
   "Specification Clarifications" section 4: "Use Of ESP In 16-Bit Code
   With 32-Bit Interrupt Handlers", which reads as follows:

   "ISSUE: When a 32-bit IRET is used to return to another privilege
   level, and the old level uses a 4G stack (D/B bit in the segment
   register = 1), while the new level uses a 64k stack (D/B bit = 0),
   then only the lower word of ESP is updated. The upper word remains
   unchanged. This is fine for pure 16-bit code, as well as pure 32-bit
   code. However, when 32-bit interrupt handlers are present, 16-bit code
   should avoid any dependence on the upper word of ESP. No changes are
   necessary in existing 16-bit code, since the only way to access ESP in
   USE16 segments is through the 32-bit address size prefix."

   The corruption happens when the Linux kernel returns control to the
   dosemu process, while a 32-bit DPMI client that uses a 16-bit data
   segment for the stack is active. This is not the usual case, but
   unfortunately some 32-bit DPMI clients are actually using a 16-bit
   segment for the stack, and even the dos4gw extender behaves that way
   sometimes.

   Programs that are known to be affected by this issue are:

     * Need For Speed 1 (demo version at least, when configured with
       sound)
     * Syndicate Wars (when used with dos4gw 0.8)
     * Open Cubic Player

   These programs are crashing shortly after startup, but this problem is
   difficult to detect reliably, so there may be many more programs that
   experience a random crashes due to this CPU bug.

   The reliable work-around was developed and added into linux-2.6.12. If
   you hit that problem, consider upgrading your linux kernel.
     _________________________________________________________________

2. Known bugs

2.1. Things YOU may help changing

2.1.1. List of currently known bugs in Dosemu 1.2.2.

     * Some documentation is known to be well out of date.
     * OPL3 FM is not implemented yet (but Midi, SB8 and SB16 work)
     * Some database programs (Clipper, FoxPro) have problems with
       locking in certain configurations. smbfs doesn't support locking.
       $_full_file_locks=(on) may or may not help.
     * Mortal Kombat 1 and 2 are not producing any sound for unknown
       reasons.
     * X-COM Apocalypse (DEMO version) locks up at startup if configured
       with sound.
     _________________________________________________________________

3. Programs exhibiting graphical problems in xdosemu

   The following programs work perfectly on the Linux console
   (suid/sudo/root) with graphics enabled but exhibit minor or major
   glitches in xdosemu.
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3.1. Games with graphical problems

   The following games exhibit glitches or don't work at all in xdosemu.
   Please let us know when any problems are solved or even better, help
   us solving!

     * Commander Keen 1 wobbles like jelly and the window shakes every
       time it scrolls.
     * Pinball Dreams 2 takes a long time to start. Once it's past the
       startup screen it runs fine though.
