En ocasiones necesitamos emular MS-DOS para ejecutar aplicaciones que llevan tiempo usándose en la empresa, que no tienen un reemplazo inmediato en Linux, y es imprescindible hallarle una solución al problema para seguir con la migración. O como en el caso que referiremos a continuación, la aplicación ya no se comercializa más, y el problema sucede cuando no hay tiempo para pensar en programar alternativas.
Existen al menos dos paquetes de software para emular MS-DOS: DOSBox y DOSEMU. Ambas tienen ventajas y desventajas. En nuestro caso particular, hemos hallado más práctico el DOSBox y a él nos referiremos.
Sucedió que necesitábamos lanzar una vieja aplicación MS-DOS que maneja relojes RTA600 de marcar entradas y salidas con tarjetas magnéticas. Por tanto, la tarea se enmarcaba en cómo utilizar los puertos serie de la PC emulando MS-DOS.
Debian 6 trae el paquete. Lo instalamos con “aptitude install dosbox” (sin comillas!), y a continuación pasamos a mirar la configuración.
Este es un ejemplo de fichero de confguración:
# This is the configurationfile for DOSBox 0.73.
# Lines starting with a # are commentlines.
# They are used to (briefly) document the effect of each option.
[sdl]
# fullscreen: Start dosbox directly in fullscreen.
# fulldouble: Use double buffering in fullscreen.
# fullresolution: What resolution to use for fullscreen: original or fixed size (e.g. 1024×768).
# windowresolution: Scale the window to this size IF the output device supports hardware scaling.
# output: What video system to use for output.
# Possible values: surface, overlay, opengl, openglnb.
# autolock: Mouse will automatically lock, if you click on the screen.
# sensitivity: Mouse sensitivity.
# waitonerror: Wait before closing the console if dosbox has an error.
# priority: Priority levels for dosbox. Second entry behind the comma is for when dosbox is not focused/minimized. (pause is only valid for the second entry)
# Possible values: lowest, lower, normal, higher, highest, pause.
# mapperfile: File used to load/save the key/event mappings from.
# usescancodes: Avoid usage of symkeys, might not work on all operating systems.
fullscreen=false
fulldouble=false
fullresolution=original
windowresolution=original
output=surface
autolock=true
sensitivity=100
waitonerror=true
priority=higher,normal
mapperfile=mapper.txt
usescancodes=true
[dosbox]
# language: Select another language file.
# machine: The type of machine tries to emulate.
# Possible values: hercules, cga, tandy, pcjr, ega, vgaonly, svga_s3, svga_et3000, svga_et4000, svga_paradise, vesa_nolfb, vesa_oldvbe.
# captures: Directory where things like wave, midi, screenshot get captured.
# memsize: Amount of memory DOSBox has in megabytes.
# This value is best left at its default to avoid problems with some games,
# though few games might require a higher value.
# There is generally no speed advantage when raising this value.
language=
machine=svga_s3
captures=capture
memsize=16
[render]
# frameskip: How many frames DOSBox skips before drawing one.
# aspect: Do aspect correction, if your output method doesn't support scaling this can slow things down!.
# scaler: Scaler used to enlarge/enhance low resolution modes. If 'forced' is appended,the scaler will be used even if the result might not be desired.
# Possible values: none, normal2x, normal3x, advmame2x, advmame3x, advinterp2x, advinterp3x, hq2x, hq3x, 2xsai, super2xsai, supereagle, tv2x, tv3x, rgb2x, rgb3x, scan2x, scan3x.
frameskip=0
aspect=false
scaler=normal2x
[cpu]
# core: CPU Core used in emulation. auto will switch to dynamic if available and appropriate.
# Possible values: auto, dynamic, normal, simple.
# cputype: CPU Type used in emulation. auto is the fastest choice. # Possible values: auto, 386, 386_slow, 486_slow, pentium_slow, 386_prefetch.
# cycles: Amount of instructions DOSBox tries to emulate each millisecond. Setting this value too high results in sound dropouts and lags. Cycles can be set in 3 ways:
# 'auto' tries to guess what a game needs.
# It usually works, but can fail for certain games.
# 'fixed #number' will set a fixed amount of cycles. This is what you usually need if 'auto' fails.
# (Example: fixed 4000)
# 'max' will allocate as much cycles as your computer is able to handle
# # Possible values: auto, fixed, max.
# cycleup: Amount of cycles to increase/decrease with keycombo.
# cycledown: Setting it lower than 100 will be a percentage.
core=auto
cputype=auto
cycles=auto
cycleup=500
cycledown=20
[mixer]
# nosound: Enable silent mode, sound is still emulated though.
# rate: Mixer sample rate, setting any device's rate higher than this will probably lower their sound quality.
# Possible values: 22050, 44100, 48000, 32000, 16000, 11025, 8000, 49716.
# blocksize: Mixer block size, larger blocks might help sound stuttering but sound will also be more lagged.
# Possible values: 2048, 4096, 8192, 1024, 512, 256.
# prebuffer: How many milliseconds of data to keep on top of the blocksize.
nosound=false
rate=22050
blocksize=2048
prebuffer=10
[midi]
# mpu401: Type of MPU-401 to emulate.
# Possible values: intelligent, uart, none.
# mididevice: Device that will receive the MIDI data from MPU-401.
# Possible values: default, win32, alsa, oss, coreaudio, coremidi, none.
# midiconfig: Special configuration options for the device driver. This is usually the id of the device you want to use. See README for details.
mpu401=intelligent
mididevice=default
midiconfig=
[sblaster]
# sbtype: Type of sblaster to emulate.
# Possible values: sb1, sb2, sbpro1, sbpro2, sb16, none.
# sbbase: The IO address of the soundblaster.
# Possible values: 220, 240, 260, 280, 2a0, 2c0, 2e0, 300.
# irq: The IRQ number of the soundblaster.
# Possible values: 7, 5, 3, 9, 10, 11, 12.
# dma: The DMA number of the soundblaster.
# Possible values: 1, 5, 0, 3, 6, 7.
# hdma: The High DMA number of the soundblaster.
# Possible values: 1, 5, 0, 3, 6, 7.
# sbmixer: Allow the soundblaster mixer to modify the DOSBox mixer.
# oplmode: Type of OPL emulation. On 'auto' the mode is determined by sblaster type. All OPL modes are Adlib-compatible, except for 'cms'.
# Possible values: auto, cms, opl2, dualopl2, opl3, none.
# oplemu: Provider for the OPL emulation. compat might provide better quality (see oplrate as well).
# Possible values: default, compat, fast.
# oplrate: Sample rate of OPL music emulation. Use 49716 for highest quality (set the mixer rate accordingly).
# Possible values: 22050, 49716, 44100, 48000, 32000, 16000, 11025, 8000.
sbtype=sb16
sbbase=220
irq=7
dma=1
hdma=5
sbmixer=true
oplmode=auto
oplemu=default
oplrate=22050
[gus]
# gus: Enable the Gravis Ultrasound emulation.
# gusrate: Sample rate of Ultrasound emulation.
# Possible values: 22050, 44100, 48000, 32000, 16000, 11025, 8000, 49716.
# gusbase: The IO base address of the Gravis Ultrasound.
# Possible values: 240, 220, 260, 280, 2a0, 2c0, 2e0, 300.
# gusirq: The IRQ number of the Gravis Ultrasound.
# Possible values: 5, 3, 7, 9, 10, 11, 12.
# gusdma: The DMA channel of the Gravis Ultrasound.
# Possible values: 3, 0, 1, 5, 6, 7.
# ultradir: Path to Ultrasound directory. In this directory
# there should be a MIDI directory that contains
# the patch files for GUS playback. Patch sets used
# with Timidity should work fine.
gus=false
gusrate=22050
gusbase=240
gusirq=5
gusdma=3
ultradir=C:\ULTRASND
[speaker]
# pcspeaker: Enable PC-Speaker emulation.
# pcrate: Sample rate of the PC-Speaker sound generation.
# Possible values: 22050, 44100, 48000, 32000, 16000, 11025, 8000, 49716.
# tandy: Enable Tandy Sound System emulation. For 'auto', emulation is present only if machine is set to 'tandy'.
# Possible values: auto, on, off.
# tandyrate: Sample rate of the Tandy 3-Voice generation.
# Possible values: 22050, 44100, 48000, 32000, 16000, 11025, 8000, 49716.
# disney: Enable Disney Sound Source emulation. (Covox Voice Master and Speech Thing compatible).
pcspeaker=true
pcrate=22050
tandy=auto
tandyrate=22050
disney=true
[joystick]
# joysticktype: Type of joystick to emulate: auto (default), none,
# 2axis (supports two joysticks),
# 4axis (supports one joystick, first joystick used),
# 4axis_2 (supports one joystick, second joystick used),
# fcs (Thrustmaster), ch (CH Flightstick).
# none disables joystick emulation.
# auto chooses emulation depending on real joystick(s).
# Possible values: auto, 2axis, 4axis, 4axis_2, fcs, ch, none.
# timed: enable timed intervals for axis. (false is old style behaviour).
# autofire: continuously fires as long as you keep the button pressed.
# swap34: swap the 3rd and the 4th axis. can be useful for certain joysticks.
# buttonwrap: enable button wrapping at the number of emulated buttons.
joysticktype=auto
timed=true
autofire=false
swap34=false
buttonwrap=true
[serial]
# serial1: set type of device connected to com port.
# Can be disabled, dummy, modem, nullmodem, directserial.
# Additional parameters must be in the same line in the form of
# parameter:value. Parameter for all types is irq.
# for directserial: realport (required), rxdelay (optional).
# (realport:COM1 realport:ttyS0).
# for modem: listenport (optional).
# for nullmodem: server, rxdelay, txdelay, telnet, usedtr,
# transparent, port, inhsocket (all optional).
# Example: serial1=modem listenport:5000
# Possible values: dummy, disabled, modem, nullmodem, directserial.
# serial2: see serial1
# Possible values: dummy, disabled, modem, nullmodem, directserial.
# serial3: see serial1
# Possible values: dummy, disabled, modem, nullmodem, directserial.
# serial4: see serial1
# Possible values: dummy, disabled, modem, nullmodem, directserial.
serial1=directserial realport:ttyS0
serial2=directserial realport:ttyS1
serial3=directserial realport:ttyS2
serial4=directserial realport:ttyS3
[dos]
# xms: Enable XMS support.
# ems: Enable EMS support.
# umb: Enable UMB support.
# keyboardlayout: Language code of the keyboard layout (or none).
xms=true
ems=true
umb=true
keyboardlayout=auto
[ipx]
# ipx: Enable ipx over UDP/IP emulation.
ipx=false
[autoexec]
# Lines in this section will be run at startup.
mount c /home/personal/Documentos/RTA600
mount e /home/personal/Descargas
(Fin del fichero de configuración)
Como vemos, la solución consiste en declarar siguientes líneas en el fichero de configuración de DOSBox:
serial1=directserial realport:ttyS0
serial2=directserial realport:ttyS1
serial3=directserial realport:ttyS2
serial4=directserial realport:ttyS3
Ojo, que debo modificar el fichero de configuración DOSBox del usuario que utilice la aplicación. Si se ejecuta como administrador, hay que modificar el del usuario root.
Por supuesto que para lanzar una aplicación habrá que tocar algunas otras cosas. Por ejemplo, habrá que declarar dónde pondré a “C:”. Eso lo veo en las líneas mount.