Search found 37 matches

by vbdasc
Sun 27 Mar, 2022 10:06 am
Forum: General
Topic: Weird A20-related behaviour (bug?)
Replies: 11
Views: 1890

Re: Weird A20-related behaviour (bug?)

So how would it know to look for [8] in the data segement, e.g. (0:8), and [108] in the extra segment, e.g. fff0:108, in your original program? I'm not sure if I understand your question correctly. But in the reference "word ptr[8]" it's assumed that DS:8 is meant. DS is the default, per ...
by vbdasc
Sat 26 Mar, 2022 10:01 am
Forum: General
Topic: Weird A20-related behaviour (bug?)
Replies: 11
Views: 1890

Re: Weird A20-related behaviour (bug?)

I think disabling A20 at the beginning of the program and then enabling it shortly afterwards might be related to the LOADFIX issue. Supposedly, there are a very small number of programs that "play games" with memory address mathematics and rely/depend on the "wraparound" that h...
by vbdasc
Fri 25 Mar, 2022 9:39 am
Forum: General
Topic: Weird A20-related behaviour (bug?)
Replies: 11
Views: 1890

Re: Weird A20-related behaviour (bug?)

I did a more elaborate test, and I think I'm beginning to understand what happens. It seems that when the setting "DOS=HIGH" is present, DOS does some arcane deep wizardry behind the scenes. It seems that when running a program from the command line (or maybe from int 21h function 4Bh) DOS...
by vbdasc
Fri 25 Mar, 2022 8:11 am
Forum: General
Topic: Weird A20-related behaviour (bug?)
Replies: 11
Views: 1890

Re: Weird A20-related behaviour (bug?)

Here's a code snippet/subroutine i use in a "real" program to test whether or not A20 is enabled. This particular code requires a 386 CPU, but could be easily modified to work on a 286 (change the CMPSD to CMPSW, and change the CX counter value for the CMPSW). This code also doesn't poten...
by vbdasc
Thu 24 Mar, 2022 3:52 pm
Forum: General
Topic: Weird A20-related behaviour (bug?)
Replies: 11
Views: 1890

Re: Weird A20-related behaviour (bug?)

Arjen42 wrote: Thu 24 Mar, 2022 3:08 pm What happens if you change the code to this?
Absolutely the same thing, without any differences in behaviour.
Arjen42 wrote: Thu 24 Mar, 2022 3:08 pm What do you mean by running it from COMMAND.COM?
It means directly from the DOS command line :)
by vbdasc
Thu 24 Mar, 2022 10:49 am
Forum: General
Topic: Weird A20-related behaviour (bug?)
Replies: 11
Views: 1890

Weird A20-related behaviour (bug?)

So, I was trying to experiment with the "DOS=HIGH" setting in Dos, and I encountered some weird behaviour that's bugging me. Or it could be entirely logical, and it might only seem weird due to my ignorance. Basically, I set up a PCem virtual machine, with IBM PC/AT BIOS, with 80286 CPU, w...
by vbdasc
Sun 06 Sep, 2020 11:57 am
Forum: General
Topic: PCem Permedia 2 emulation
Replies: 4
Views: 3451

Re: PCem Permedia 2 emulation

This is about bank registers, permedia 2 supports only 256 colors in 640x400 and in 640x480 resolutions, rest resolutions and colors depth works only in linear framebuffer. Maybe SarahWalker will know, has register documentation. She said in another thread that she had the necessary info about the ...
by vbdasc
Sat 25 Jul, 2020 8:11 am
Forum: Development
Topic: documentation rework
Replies: 13
Views: 8768

Re: documentation rework

The is no problem to include the MD5/SHA1 Well, we should wait to hear the opinion of the principial author on this. Because for some copyright purists even this could be considered an infringement. the thing is that there is not just ONE valid file. There are many versions of a same ROM and all sh...
by vbdasc
Fri 24 Jul, 2020 6:43 am
Forum: General
Topic: PCem USB support
Replies: 15
Views: 12579

Re: PCem USB support

What would the USB 'connect' to? A host port? If I'm reading properly what the person who started this thread wrote, to emulated USB devices. Who will write the emulation code for these devices? Now this is the real question :) P.S. Another possibility is, of course, adding passthrough support for ...
by vbdasc
Tue 21 Jul, 2020 1:24 pm
Forum: General
Topic: Future graphics card emulation
Replies: 112
Views: 197241

Re: Future graphics card emulation

leilei wrote: Tue 21 Jul, 2020 11:41 am Probably because it's not worth the effort for all the funny wonky affine texture mapping the Laguna3D's notoriously known for.
Thanks, I didn't know about that. A weird feature that is hard to implement is definitely an argument against the card.
by vbdasc
Tue 21 Jul, 2020 11:18 am
Forum: General
Topic: Future graphics card emulation
Replies: 112
Views: 197241

Re: Future graphics card emulation

> If the card you're thinking of isn't listed then it probably isn't interesting enough to be worth emulating. Forgive me for this (probably) stupid question, but is there any objective criteria for a card to be considered interesting/worthy? IMHO, the performance of the real thing shouldn't play a ...
by vbdasc
Thu 13 Feb, 2020 8:46 am
Forum: General
Topic: Request - Rendition Verite V1000
Replies: 3
Views: 4684

Re: Request - Rendition Verite V1000

It is possible to add this card in the next release of PCem? The Verite V1000? I'm wanting to emulate their video APIs - RRedline and Speedy3D - under Win95. Thanks :) Why would you want Verite support in PCem only to emulate Rendition APIs? IMHO, a PCem with Verite support would emulate a real PC ...
by vbdasc
Thu 28 Sep, 2017 8:08 am
Forum: Development
Topic: v13 feature freeze end of Friday 13th October
Replies: 19
Views: 18336

Re: v13 feature freeze end of Sunday 8th October

V13? This can't possibly be good... I'd suggest going straight to version 14...

But OTOH, it's amazing how far did PCem go since its early days... Congratulations and thanks!
by vbdasc
Mon 05 Jun, 2017 9:38 am
Forum: General
Topic: Expanded Memory Boards for 8088/8086 machines?
Replies: 18
Views: 16635

Re: Expanded Memory Boards for 8088/8086 machines?

Sadly, technical info about EMS boards seems very scarce...
by vbdasc
Mon 15 May, 2017 9:38 am
Forum: General
Topic: IBM PS/2 Model 55SX can't boot from ESDI hard disk
Replies: 7
Views: 7359

Re: IBM PS/2 Model 55SX can't boot from ESDI hard disk

The Wikipedia article on the PS/2 states that the Model 55SX has support for the ESDI controller while the Model 50 doesn't. The Model 50 has to rely on HDD controllers other than ESDI. IMHO, if Wikipedia says that, then it's wrong on this one. AFAIK, both model 50 and 55 (and 70) can support "...
by vbdasc
Mon 15 May, 2017 6:59 am
Forum: General
Topic: IBM PS/2 Model 55SX can't boot from ESDI hard disk
Replies: 7
Views: 7359

Re: IBM PS/2 Model 55SX can't boot from ESDI hard disk

> I bet that the inability to boot from the ESDI hard disk also affects the emulated IBM PS/2 Model 50 and IBM PS/2 Model 80 as well, but those machines have not been tested at this time.

Note that the ESDI controller in model 80 is very different and incompatible with that in models 50 and 55.
by vbdasc
Fri 12 May, 2017 7:04 am
Forum: General
Topic: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR
Replies: 37
Views: 26403

Re: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR

Battler wrote:Doesn't early OS/2 use 286 protected mode? That would make it a good candidate for testing.
Yes, OS/2 ver. 1.x uses 286 protected mode, as well as Microport System V/AT Unix, some versions of Xenix and even Minix, and others. But installing and using Windows 3.x is just easier :)
by vbdasc
Fri 12 May, 2017 6:58 am
Forum: General
Topic: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR
Replies: 37
Views: 26403

Re: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR

I'm not aware of any games that use protected mode on a 286 - it doesn't really gain you much over real mode other than a larger address space (but still with 64kb segments), and if you need that then it's probably easier just to use EMS/XMS rather than write a DOS extender. By that logic, Windows ...
by vbdasc
Fri 12 May, 2017 6:55 am
Forum: General
Topic: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR
Replies: 37
Views: 26403

Re: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR

Do you know any game that uses the 286 protected mode? Any game for Windows 3.1, for example (only joking, lol). Wolfenstein 3D maybe? Nope, it runs in real mode, AFAIK. Try "Syndicate" (1993) (I'm not actually sure, but there are indications that it might be built with a 286 extender)
by vbdasc
Thu 11 May, 2017 12:03 pm
Forum: General
Topic: Support for 5.25 fd-formatted floppy
Replies: 8
Views: 6594

Re: Support for 5.25 fd-formatted floppy

Fd-format was : " A DOS tool written in Pascal by Christoph H. Hochstätter that allows users to format floppy disks to a higher than usual density, enabling the user to store up to 300 kilobytes more data on a normal high density 3.5" floppy disk" (wikipedia). It is not related with ...
by vbdasc
Thu 11 May, 2017 11:35 am
Forum: General
Topic: Support for 5.25 fd-formatted floppy
Replies: 8
Views: 6594

Re: Support for 5.25 fd-formatted floppy

I don't think any real 5.25 inch HD floppies can reliably support 18 sectors (512 bytes each) per track. Unless they're modded to spin at less than the standard 360rpm, that is.

By the way, what's exactly the size of these images?
altheos wrote:(1.6 version) floppies
What exactly does this mean?
by vbdasc
Thu 11 May, 2017 11:21 am
Forum: General
Topic: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR
Replies: 37
Views: 26403

Re: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR

ppgrainbow wrote: The Dell System 200 does work with Windows 3.0 and Windows 3.0a. I can only test this on PCem right now.
Does Windows 3.0 run in real or protected mode? What happens when you run "win /r" and "win /s"? Did you check if HIMEM.SYS from Windows 3.0 works?
by vbdasc
Thu 11 May, 2017 7:07 am
Forum: General
Topic: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR
Replies: 37
Views: 26403

Re: DELL System 200 (and others) HIMEM.SYS (MS-DOS 5.0+) GATE A20 ERROR

ppgrainbow wrote:The Dell System 200 does work with MS-DOS 3.31/MS-DOS 4.0x.
Does it work with Windows 3.1? Does it work with any protected mode software at all? If not and it can't be repaired then really there is not much reason to keep it, IMHO.
by vbdasc
Fri 21 Apr, 2017 8:21 am
Forum: General
Topic: Expanded Memory Boards for 8088/8086 machines?
Replies: 18
Views: 16635

Re: Expanded Memory Boards for 8088/8086 machines?

The 640k barrier is a convention, not a limit. The CPU can address up to 1 Mb, but DOS gets only the first 640 Kb (because memory above 0xA0000 is reserved). If the machine has an EGA or VGA-compatible videocard, then by definition, the region from 0xA0000 to 0xBFFFF is unavailable. You can place s...
by vbdasc
Wed 19 Apr, 2017 8:38 am
Forum: General
Topic: Expanded Memory Boards for 8088/8086 machines?
Replies: 18
Views: 16635

Re: Expanded Memory Boards for 8088/8086 machines?

Actually any 8088/8086 machine can't use more than 640k base memory. Are you sure? IMHO, SCP Gazelle could access 896Kb of RAM, and Altos 986 could access almost 1024K. Of course, neither of these machines was PC-compatible :) But, the idea about expanded memory boards seems good. Some DOS business...
by vbdasc
Sat 08 Apr, 2017 12:03 pm
Forum: Development
Topic: IBM PS/2
Replies: 12
Views: 10955

Re: IBM PS/2

Wow, thanks for supporting this little MCA machine, Sarah... Now, I can finally see how does this cryptic IBM ABIOS work under OS/2 1.3 :)
by vbdasc
Sat 08 Apr, 2017 11:58 am
Forum: Development
Topic: IBM PS/2
Replies: 12
Views: 10955

Re: IBM PS/2

For those who want to test the model 50, you need to create the "i8550021" folder inside "roms" and there you'll need to place one or both of these files: 90x7423.zm14 90x7426.zm16 Thanks... but didn't the PS/2 model 50-021 come with a 20Mb MFM disk, connected to a MCA ST506/412...
by vbdasc
Thu 30 Mar, 2017 10:15 am
Forum: Development
Topic: IBM PS/2
Replies: 12
Views: 10955

IBM PS/2

I'm sorry if this question has been already asked; I couldn't find anything. So, would it be possible to emulate certain IBM PS/2 models for which ROM dumps are available? For example, Model 30 with 8086 or 80286. It would be interesting to play with the MCGA :)
by vbdasc
Thu 30 Mar, 2017 9:28 am
Forum: General
Topic: PC-DOS 1.10 and PCem v12
Replies: 64
Views: 44039

Re: PC-DOS 1.10 and PCem v12

What's surprising there? Formatting without /1 formats both sides, which obviously won't work with an inserted 180k image... It works fine on real hardware. Yet no (or at least almost no) real hardware behaves like these 160K/180K/320K floppy images. So the results you got with PCDOS2 were totally ...
by vbdasc
Sun 26 Mar, 2017 8:18 pm
Forum: General
Topic: [BUG] NSSI hangs AMI WinBIOS 486 machine!
Replies: 40
Views: 27550

Re: [BUG] NSSI hangs AMI WinBIOS 486 machine!

You people didn't understand my point, or I expressed myself in the wrong way. Of course all current PCem support IDE! What I meant was clone 286 and 386 (by clone I mean those motherboards you purchase alone so you can assemble a PC yourself) don't have an integrated/onboard IDE interface, you'll ...