EMU2: A simple text-mode x86 + DOS emulator

This is a simple DOS emulator for the Linux text console, supporting basic DOS system calls and console I/O.

Using the emulator

To run a DOS .exe or .com file, simply load it with

emu2 myprog.exe

The emulator accepts some options in the command line and more options as environment variables, this allows child process (programs run by your DOS program) to inherit the configuration.

The full usage is:

emu2 [options] <prog.exe> [args...] [-- environment vars]

Options (should be placed before the DOS program name):

• -h Shows a brief help.

• -b addr Load header-less binary at given address (to load ROMs or test data).

• -r <seg>:<ip> Specify a run address to start execution (only for binary loaded data).

The available environment variables are:

• EMU2_DEBUG_NAME Base name of a file to write the debug log, defaults to the exe name if not given.

• EMU2_DEBUG List of debug options to activate, from the following: cpu, int, port, dos, video.

• EMU2_PROGNAME DOS program name, if not given try to convert the unix name to an equivalent DOS path.

• EMU2_DEFAULT_DRIVE DOS default (current) drive letter, if not given use C:

• EMU2_CWD DOS current working directory, if not given tries to convert the current directory to the equivalent DOS path inside the DOS default drive, or C:\ if not possible.

• EMU2_DRIVE_n Set unix path as root of drive n, by default all drives point to the unix working directory.

• EMU2_APPEND Sets a list of paths to search for data files on open, emulating the DOS APPEND command. Only files with a relative path are included in the search, and the search is relative to the current working directory if no drive letter is specified in the append path. For example, if set to "TXT;C:\IN", when opening the file "CAT.TXT" the file is searched as "CAT.TXT", "TXT\CAT.TXT" and "C:\IN\CAT.TXT" in turn.

• EMU2_CODEPAGE Set DOS code-page to the specified string. Set to '?' to show list of included code-pages, multiple aliases separated with commas. Set to a file name to read the mapping table from a file with the unicode value for each byte. You can download mapping tables from ftp://ftp.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/PC/ The code-page setting affects keyboard input and screen output, but does not change the DOS NLS information. The default code-page is CP437.

• EMU2_LOWMEM Limits main memory to 512KB, this fixes some old DOS programs with a bug that checks available memory using "signed" comparison instructions (JLE instead of JBE). This is needed at least for MASM versions 1.0 and 1.10.

• EMU2_DOSVER Changes the reported DOS version, allowing programs that checks this version to run. You can specify a major version or a major dot minor, for example "3.20", "2.11" or "5".

• EMU2_ROWS Setups the VGA text mode to the given number of rows, from 12 to 50 at the program start. Some full-screen DOS programs will retrieve this info and adjust the screen properly, some other will ignore this and setup the text mode again.

Simple Example

For a simple example, we can run the Turbo Pascal 3, available from the antique software collection as a file tp302.zip.

First, make a new directory and unzip the file:

$ mkdir tp302
$ cd tp302
$ unzip ../tp302.zip
$ ls
$ ls
$ ls
ACCESS3.BOX   CALC.PAS      DEMO-BCD.PAS  GRAPH.P     SUBDIR.PAS    TURBO.COM
ART.PAS       CMDLINE.PAS   EXTERNAL.DOC  LISTER.PAS  TINST.COM     TURBO.MSG
CALCDEMO.MCS  COLOR.PAS     GETDATE.PAS   README      TINST.MSG     TURTLE.PAS
CALC.HLP      DEMO1-87.PAS  GETTIME.PAS   README.COM  TURBO-87.COM  WINDOW.PAS
CALC.INC      DEMO2-87.PAS  GRAPH.BIN     SOUND.PAS   TURBOBCD.COM
$ chmod +w *

The last is necessary as you will want to to modify the program files afterwards.

The main file is named "TURBO.COM", there is also a "README.COM" to read further info, try that:

$ emu2 README.COM

You can press exit to return to the command line. Now, you can configure the compiler, as the README said, just load TINST.COM, press "S" (screen type), "0" (default), "N" (screen does not blink) and "Q" to quit.

$ emu2 TINST.COM

                   TURBO Pascal installation menu.
             Choose installation item from the following:

[S]creen type |  [C]ommand installation  |  [M]sg file path  |  [Q]uit


                         Enter S, C, M or Q: 

Choose one of the following displays:

  0)  Default display mode
  1)  Monochrome display
  2)  Color display 80x25
  3)  Color display 40x25
  4)  b/w   display 80x25
  5)  b/w   display 40x25

Which display? (Enter no. or ^Q to exit):

Does your screen blink when the text scrolls? (Y/N):

Finally, we are ready to run the program:

$ emu2 TURBO.COM
----------------------------------------
TURBO Pascal system        Version 3.02A
                                  PC-DOS
                                        
Copyright (C) 1983,84,85,86 BORLAND Inc.
----------------------------------------
                                        
Default display mode                    
                                        
                                        
                                        
Include error messages (Y/N)?           

Logged drive: C                         
Active directory: \                     
                                        
Work file:                              
Main file:                              
                                        
Edit     Compile  Run   Save            
                                        
Dir      Quit  compiler Options         
                                        
Text:     0 bytes                       
Free: 62024 bytes                       
                                        
>                                       

Try loading a program, use "e" to edit, type "window.pas", and you are in the editor:

      Line 1    Col 1   Insert    Indent  C:WINDOW.PAS                          
program TestWindow;                                                             
{$C-}                                                                           
{                                                                               
              WINDOW DEMONSTRATION PROGRAM  Version 1.00A                       
                                                                                
       This program demonstrates the use of windows on the IBM PC               
       and true compatibles.                                                    
                                                                                
       PSEUDO CODE                                                              
       1.  MakeWindow        - draws window boxes on the screen                 
       2.  repeat                                                               
             UpdateWindow 1  - scrolls the window contents up or                
                               down for each window.                            
             UpdateWindow 2                                                     
             UpdateWindow 3                                                     
           until a key is pressed                                               
       3.  Reset to full screen window                                          
                                                                                
       INSTRUCTIONS                                                             
       1.  Compile this program using the TURBO.COM compiler.                   
       2.  Type any key to exit the program.                                    
}                                                                               

To exit the editor, type "CONTROL+K" and "D", in the prompt you can now type "R" to compile and run the program.

Advanced Example

For a more advanced example, we can install and run Turbo Pascal 5.5, available from the same antique software collection as a file tp55.zip.

First, make a new directory and unzip the file:

$ mkdir tp55
$ cd tp55
$ unzip ../tp55.zip
$ ls
Disk1 Disk2

As you see, the program was distributed in two disks, and must be installed before running.

To install, let's first copy all the contents to one directory:

$ mkdir all
$ cp -r Disk1/* Disk2/* all/

And now, run the emulator giving the correct paths to simulate a floppy drive:

$ EMU2_DEFAULT_DRIVE=A EMU2_DRIVE_A=all emu2 all/INSTALL.EXE

Type enter, enter again to install from drive "A", again to install on a hard-drive, go down to "Start Installation" and enter again. The install program shows an error, this is because we copied all the content to one drive. Simply type "S" to skip all errors.

After the installation is finished, we must run the install again, to copy the missing files from before, with the same command line:

$ EMU2_DEFAULT_DRIVE=A EMU2_DRIVE_A=all emu2 all/INSTALL.EXE

Again, press enter to the questions and go to "Start Installation", this time will complete without errors.

You can now compile from the command line, as:

$ emu2 tp/tpc.exe -- 'PATH=C:\TP'
Turbo Pascal Version 5.5  Copyright (c) 1983,89 Borland International
Syntax: TPC [options] filename [options]
/B	Build all units		/$A-	No word alignment
/Dxxx	Define conditionals	/$B+	Complete boolean evaluation
/Exxx	EXE & TPU directory	/$D-	No debug information
/Fxxx	Find run-time error	/$E-	No 8087 emulation
/GS	Map file with segments	/$F+	Force FAR calls
/GP	Map file with publics	/$I-	No I/O checking
/GD	Detailed map file	/$L-	No local debug symbols
/Ixxx	Include directories	/$Mxxx	Memory allocation parameters
/L	Link buffer on disk	/$N+	8087 code generation
/M	Make modified units	/$O+	Overlays allowed
/Oxxx	Object directories	/$R+	Range checking
/Q	Quiet compile		/$S-	No stack checking
/Txxx	Turbo directories	/$V-	No var-string checking
/Uxxx	Unit directories
/V	EXE debug information

$ emu2 tp/tpc.exe tp\\qsort.pas -- 'PATH=C:\TP'
Turbo Pascal Version 5.5  Copyright (c) 1983,89 Borland International
TP\QSORT.PAS(66)
66 lines, 4384 bytes code, 2668 bytes data.

$ emu2 tp/qsort.exe
....

And for the IDE, you can use:

emu2 tp/turbo.exe  -- 'PATH=C:\TP'