DOS related FAQ

- 1. FB is a 32-bit compiler - do I need a 32-bit DOS?
- 2. What about FreeDOS-32? Does/will FB work, is/will there be a version?
- 3. When running FreeBASIC in DOS, I get a 'Error: No DPMI' message!
- 4. Is there a possibility how to get rid of this CWSDPMI.EXE and CWSDPMI.SWP?
- 5. Can I use other DOS extenders, like DOS/4GW, Causeway, DOS/32A?
- 6. Where is the nice blue screen with all the ... / where is the IDE?
- 7. How can I view the documentation in CHM or PDF format in DOS?
- 8. How can I write/edit my source code?
- 9. How can I play sound in DOS?
- 10. How can I use USB in DOS?
- 11. How can I use graphics in DOS?
- 12. DEF SEG is missing in FB! How can I workaround this in my code?
- 13. How can I rewrite QB's CALL INTERRUPT / access the DOS and BIOS interrupts?
- 14. How can I rewrite QB's XMS/EMS handling?
- 15. FBC gives me a 'cannot find lsupcxx' error!
- 16. How can I use the serial or parallel port?
- 17. How can I use a printer?
- 18. How can I make a screenshot of a FreeBASIC program running in DOS?
- 19. Graphics mode doesn't work (freeze / black screen / garbage output)!
- 20. Mouse trouble! Mouse doesn't work at all in DOS / arrow 'jumps' / etc. ...
- 21. What about the 64 KiB and 640 KiB problems / how much memory is supported by FB in DOS?
- 22. My program crashes when I try to use more than cca 1 MiB RAM! Is this a bug in FreeBASIC?
- 23. Threading functions are disallowed in DOS? Help!
- 24. Executables made with FB DOS are bloated!
- 25. Compilation is very slow with FB!
- 26. SLEEP doesn't work! How can I cause a delay?
- 27. The performance is very bad in DOS!
- 28. Can I access disk sectors with FB?
- 29. Can I use inline ASM with advanced instructions like SSE in DOS ?

No, the DOS version of FreeBASIC uses a DOS extender, allowing you to execute 32-bit code on top of a 16 bit DOS kernel. You can use FreeDOS (16-bit), Enhanced-Dr-DOS, old closed Dr-DOS, or even MS-DOS down to version cca 4. You need at least 80386 CPU, see also Requirements.

FreeDOS-32 is experimental at time of writing, but it should execute FreeBASIC and applications generated by it with no change. While FB DOS support already works on FreeDOS (16), it should be ready for FreeDOS-32 as well.

You need a DPMI host (DPMI kernel, DPMI server), means the file "CWSDPMI.EXE" (cca 20 KiB) or HDPMI32.EXE (cca 34 KiB). See requirements, and FAQ 4 for more details.

Yes, 2 possibilities. To get rid of CWSDPMI.EXE and create a standalone DOS executable embedding CWSDPMI, you need the CWSDPMI package and the "EXE2COFF.EXE" file. Using EXE2COFF, you remove the CWSDPMI.EXE loader (file loses 2 KiB of size, resulting in a "COFF" file without extension), and then glue the file "CWSDSTUB.EXE" before this COFF. The new executable is cca 21 KiB bigger than the original one, but it is standalone, no additional files are needed. To get rid of CWSDPMI.SWP, you can then edit your executable with CWSPARAM.EXE, and disable the swapping (occasionally also - incorrectly - referred as paging). Note, however, that this will limit the memory that can be allocated to the amount of physical memory that is installed in a system. This work can be done both with the FBC.EXE file and all executables created by FBC. The method is also described in the CWSDPMI docs in the package. Alternatively, you can use the WDOSX or D3X extender. They don't swap and create standalone executables. Since they run your executable in Ring 0, the crash handling of them is not very good and can cause freezers or reboots on bugs where other hosts exit the "civil" way with a register dump. Also, spawning might not work well / at all with WDOSX or D3X. Finally, you can use HDPMI . Download the "HXRT.ZIP" file (here: japheth.de/HX.html), extract "HDPMI32.EXE" (cca 34 KiB) and "HDPMI.TXT" (not required by the code, just for your information), and include it to your DOS startup ("HDPMI32 -r"). This will make HDPMI resident and prevent all FreeBASIC (also FreePASCAL and DJGPP) programs from both crying about missing DPMI and swapping. HDPMI can not (easily / yet) be included into your executables. Running an executable containing D3X, CWSDPMI or some DPMI host inside under HDPMI or other external host is fine - the built-in host will be simply skipped. Using DPMI is definitely required for FreeBASIC, since it can't generate 16-bit real mode code, and there is no other good way to execute 32-bit code in DOS.

Not any extender around. So-called WATCOM-like extenders can't be used because of important differences in memory management and executable structure. WDOSX and D3X do work, since they are a multi-standard extenders, not only WATCOM-like. You also can use PMODE/DJ (not "original" Tran's PMODE, nor PMODE/W (!), saves cca 5 KiB compared to CWSDPMI, can be included into the EXE, but might affect stability or performance) or, as aforementioned, HDPMI.

The FreeBASIC project focuses on the compiler, generating the executables from your BAS sources. It looks unspectacular, but is most important for the quality of software developed by you. The project does not include an IDE. There are several external IDEs for FreeBASIC, but probably none does have a DOS version by now. If you really need one, you could try Rhide, but note that it is complicated and buggy, so use it at your own risk. See also FAQ 7 and 8.

There is no good way to view CHM or PDF files in DOS by now. But you can view the FreeBASIC documentation nevertheless. One of the FreeBASIC developers, coderJeff provides a FreeBASIC documentation viewer with the docs included in a special format, and having also a DOS version. It looks similar the QB's built-in help viewer, but does not contain an editor or IDE. Download here: http://www.execulink.com/~coder/FreeBASIC/docs.html

There are many editors for DOS around, but only few of them are good - some possibilities are FreeDOS EDIT (use version 0.7d (!!) or 0.9, 64 KiB limit, suboptimal stability (save your work regularly) ), SETEDIT, INFOPAD (comes with CC386 compiler, can edit big texts also, has syntax highlighting for C and ASM, but not for BASIC).

There are 2 ways how to play sound in DOS: either the ("archaic") PC speaker, famous for beeping if something goes wrong, or a soundcard. The speaker is easy to control, allows more than one might think, even to play audio files (WAV, with decompression code also OGG Vorbis, MP3 etc.), you can re-use most of existing QB code easily (example: o-bizz.de/qb...speaker.zip) or ASM code via inline ASM, but provides one channel and 6 bits only, and of course significantly worse quality than a soundcard, and, on some newest (P4) PC's the speaker quality is very bad or there is no speaker at all. For old ISA soundcards, there is much example code around, a newer PCI soundcard can be accessed (supposing bare DOS in this category) either using a ( "emulation" SB16 compatible) driver, if it is available for your card (unfortunately, this is becoming more and more a problem, the DOS drivers are poor or even inexistent), or access the card directly (this is low-level programming, hardware-related, assembler is also needed, and you need technical docs about the card). There are a few sources of inspiration like the DOS audio player MPXPLAY (written in C with some ASM), supporting both methods (native + "emu" drivers), see an up-to-date list here: drdos.org/...wiki...SoundCardChip. Support of sound in DOS is not business FB DOS port, actually FB doesn't "support" sound on Win32 and Linux either - the games "connect to the API" rather than use FreeBASIC commands or libraries. To play compressed files (MP3, OGG Vorbis, FLAC, ...) , you additionally need the decompressing code, existing DJGPP ports of those libraries should be usable for this.

Again, not business of FB, you need a driver, FB doesn't "support" USB on Win32 or Linux either, see other Wiki: drdos.org/...wiki...USB about possibilities of USB usage in DOS.

GUI or graphics in DOS is definitely possible, there are several approaches:

Note that some graphic cards report limited features through VESA, most notably less memory (for example 8 MiB instead of 64 MiB) or less modes (for example only 24 bpp modes visible while 32 bpp hidden, only lower resolutions visible (up to cca 1280x1024) while higher hidden, only "4:3" modes visible while "wide" modes hidden). This is a problem of the card, not of DOS or FreeBASIC. You will see the additional features in systems other than DOS, or in DOS only using hardware detection tools going to the lowest level bypassing VESA.

DEF SEG is related to 16-bit RM addressing and was removed because of this. "direct" access to VGA or other low memory areas is not possible, because FreeBASIC's memory model (same as DJGPP's) is not zero-based. For accessing low DOS memory, use DOSMEMGET and DOSMEMPUT , see "vga13h.bas" example, or "_dos_ds" selector for inline ASM, see example:

Those interrupts can be accessed only using the DOS version/target of FB.

The access to interrupts is slower than in QB: with FB the DPMI host will have to do 2 context switches, going to real-mode and coming back. All of that will eat hundreds of clocks in raw DOS and thousands of clocks if emm386 is loaded or if inside a Windows' DOS box. The slow down might be negligible or relevant, it depends. You should try to minimize the number of such calls, and process more data per call - at least several KiB, not just one byte or a few bytes.

Use DJGPP's DPMI wrapper:

Alternatively you can call INT's via inline ASM, 2 important things you have to care about are the fact that FB's memory model is not zero-based (see also FAQ 12, "DEF SEG" issues), and additionally "direct" passing of addresses (like DS:[E]DX) to an INT will not work except you have a DPMI host with "DOS API translation".

Depends why original code uses it. If it's just to bypass low memory limits, simply remove it and use "ordinary" FB's data types / memory handling features instead. If it is used for (sound) DMA, you are out of luck and have to redesign the code completely, about sound see FAQ 9. For DMA use preferably the low memory (should be no big problem, since the application code and most buffers are in DPMI memory instead), DMA in DPMI memory is possible but more difficult.

The source of this problem is the libsupcxx.a file in LIB\DOS\ directory, having 9 characters in the name. Your fault is to have extracted the ZIP with long file names enabled, usually in Windows, and then using FB in DOS with no LFN support, resulting in this file looks LIBSUP~1.A and can't be found. Rename the file in LIBSUPCX.A (one X only) or extract the ZIP again in DOS. Note: changes in FB 0.18, retest needed.

The DOS INT14 is not very useful/efficient as it sends/reads a single char in each call. So it's better to use an external DOS32 comms library. /* does someone know a good one ? */ FB up to 0.18.2 doesn't support OPEN COM on DOS target, coderJeff has an experimental library/driver available, included with FB since 0.18.3.

DOS kernel won't help you here, so you have to prepare the text (trivial) or pixel data (acceptably easy for printers compatible with the "ESC/P" standard) yourself and send in to the printer via the parallel port or USB using an additional driver (see FAQ 10). So-called "GDI" or "Windows" printers can't be made working in DOS with reasonable effort.

Ideally include this feature into your own code. DOS TSR based screenshooters like SNARF mostly will work with text based screens, but probably none of them with FreeBASIC's GFX library. It's not really a bug on one or other side, it's a problem "by design".

Place a bug report into the forum. To make it as useful and productive as possible, please beware of the following, proceed given steps and provide all related information:

RayeR's VESATEST and CPUID can be downloaded here: rayer.ic.cz/programm/programe.htm , VBEDIAG here drv.nu/vbediag/.

To use a mouse in DOS, you need a compatible driver, recognizing your mouse, and recognized by FreeBASIC library. For optimal results, you need a good driver and a suitable mouse.

Mouse: the optimal choice, and pretty well available nowadays, is a PS/2 mouse. The old type would be a serial mouse, also this one should work. The newest is USB mouse - but is not very suitable for use in DOS, since it would need a compatible (INT33) high quality native USB mouse driver (none available by now, only some experimental), or rely on BIOS emulation (not always available, or "unprecise").

Driver: the preferred choice is CTMOUSE from FreeDOS project. There are versions 1.9a1, 2.0a4, and 2.1b4 from 2008-July available. It is included with (but not limited to) FreeDOS, or download a version from here: ibiblio.org/pub/...mouse . None of them is perfect, but still they are well usable and better than most competitors. 1.9xx and 2.1xx will cooperate with BIOS, allowing USB emulation, 2.0xx bypasses BIOS and thus USB emulation will NOT work. Also Logitech mouse drivers usually do a good job, download from here: uwe-sieber.de/util_e.html - version 6.50 is a good start. Known for problems are DRMOUSE and some (old ?) versions of MSMOUSE.

If the mouse does not work at all, then most likely the driver is not loaded, doesn't recognize the mouse (see driver messages), or is not compatible with the INT33 "standard". For USB mouse, activating the "USB mouse emulation" in BIOS settings can help.

If the mouse control is "unprecise", the arrow "jumps" , then you either have a bad driver - use a better one, or the BIOS emulation is bad - the solution is to buy a PS/2 mouse then.

Memory management is business of the DPMI host, rather than the compiler. FreeBASIC and executables generated by it do not suffer from this problem, since they use 32-bit DPMI code, rather than real mode. You can use almost all the memory of your PC, with some limitations, but they are far above 64 or 640 KiB. CWSDPMI r5 is verified to work well up to 512 MiB only, additional memory does not crash it (unlike some older versions), but is silently ignored. HDPMI is supposed to support more: up to 4 GiB (the limit of 32-bit addressing), but there was not much testing on such huge machines - verified up to cca 1.5 GiB. FreeBASIC and code generated by it do not require classical DOS based memory managers (HIMEM/XMS and EMM386/EMS), but are supposed to coexist with them if they are present. All this of course applies to true DOS only, things like "Dos Box" will keep the control over the memory management and provide only a small piece of memory (depends, up to cca 64 MiB) to your DOS code.

No, it's not a bug in FreeBASIC and it's not really DOS specific, see also Compiler FAQ. For a beginner, the easy solution is to use Shared for arrays. More advanced users could consider using memory management functions like Allocate. This is even more important in DOS, since it allows the application to run on (old) PCs with little memory (and still edit at least small texts for example), as well as to use all huge RAM if available (and edit huge texts for example).

The Threading Support Functions are not supported for DOS target, and most likely won't be soon/ever. The reason is simple: neither the DOS kernel, nor the DPMI host/standard, nor "GO32" DOS Extender support threading, unlike the Win32 or Linux kernel. However nothing is impossible in DOS: you can set up your threading on the top of DPMI. There are multiple possibilities, two of which are:

This is true but there is no easy/fast way to fix. FB is a 32-bit HLL compiler, and most of the size is imported from DJGPP. !writeme! (see forum: t=11757)

Problem: "FBC takes 10 seconds to compile a "Hello world" program ! TurboBASIC / QBASIC / VBDOS / PowerBASIC do take < 1 second for the same job ..."

True, but this is "by design": FB compiles your sources in 3 steps, saving the intermediate files, as described in CompilerCmdLine, while many older compilers do just 1 pass in memory. This is related mostly to file I/O performance, see FAQ 27 below about possibilities of improvements, additionally a small improvement can be achieved here by making the DPMI host resident (HDPMI32 -r or CWSDPMI -p , see FAQ 4 above). Note that the delay is mostly "additive" , so it won't hurt too much with bigger projects.

Sleep does work ... but has a resolution of cca 55ms = 1/18s only, thus "SLEEP 500" is fine, while for example using "SLEEP 2" for 2 milliseconds won't work. !writeme! / !fixme!

Problem: "The performance in DOS is poor compared to Win32 / Linux binary compiled from the very same source !" or "Even worse, the very same DOS binary runs much faster in NTVDM than in DOS !"

Both indeed can happen, nevertheless, DOS is no way predestined to be slow, the inefficiencies can be fixed. First you have to identify the area where you code looses performance.

You can ... but FreeBASIC won't help you too much here: no "portable" solution, use OS specific low level way. For DOS 3 methods are possible

Note that such experiments are a bit "dangerous" - you can easily lose data or make your PC unbootable if something goes wrong.

You can ... but SSE2 and above need to get enabled before. This is usually considered as business of the DPMI host, HDPMI32 and CWSDPMI 7 will do that, most other hosts won't. Make sure to properly CPUID for such instructions before using them. It's a good idea to provide a code branch compatible with older CPU's (early Pentium, 80386) besides supporting latest instructions, and to avoid CMOV in those too.