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Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-12, 09:46

in PC Emulation

in PC Emulation

This is the first time the read gives invalid information: 0:00:18:02.7.0000: ModR/M address: 0000:FFFF8000=FFFF8000 0:00:18:02.8.0000: 0000:7E48 (8B)MOVW AX,[DS:SI-8000] 0:00:18:02.8.0000: Registers: 0:00:18:02.8.0000: AX: 0000, BX: 0003, CX: 0005, DX: 0000 0:00:18:02.8.0000: CS: 0000, DS: 0000, ES …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-10, 22:56

in PC Emulation

in PC Emulation

How do you mean '+'? The unsigned number 0x8000 equals -32768 when read as a signed value from memory (bit 15 equalling a value of -32768). So the value is -32768 + value&0x7FFF = -32768 + 0 = -32768, converted to hex -8000. This value is added to the address offset computated, so SI + -8000 = SI- …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-10, 14:29

in PC Emulation

in PC Emulation

0000:7C9E (03)ADDB AL,BL This disassembly is improper, based on the affected registers (->ADDB AX,BX). The debugger log doesn't show the code getting anywhere near where you show the latest problem. 0000:7E48 (8B)MOVW AX,[DS:SI-17FFF] This disassembly is improper, and the value that is fetched is …

Re: VGA CRTC mode control byte/word bit reversed?

Posted on 2015-03-09, 22:19

in DOSBox Development

in DOSBox Development

Won't that give problems with games relying on that bit to work correctly?

VGA CRTC mode control byte/word bit reversed?

Posted on 2015-03-09, 20:45

in DOSBox Development

in DOSBox Development

When I look at the I/O for setting the bit it says: If clear system is in word mode. Addresses are rotated 1 position up 343 bringing either bit 13 or 15 into bit 0. When I compare this to the other VGA documentation, it seems correct. But when I look at the int10_modes.cpp code it's reversed (set …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-07, 11:05

in PC Emulation

in PC Emulation

@SarahWalker: The log is already 3 posts back (The debuggerlog.zip file contains the log). I think that the problem lies in how IO.SYS is loaded: First sector 19 is read, which contains the FAT root directory. Next the first sector containing the contents of IO.SYS is looked up. I think that the …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-07, 10:19

in PC Emulation

in PC Emulation

The zip file I attached to a few posts back contains the assembly executed up to that point. Looking at the data read, which is supposed to be IO.SYS, I notice, when comparing it to the IO.SYS extracted using Winimage, that it's wrong. So the first sector (19) read is correct (It's the root …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-06, 11:46

in PC Emulation

in PC Emulation

It's currently running till the REP MOVSB at 0070:0233 ends. After that it does something strange: 0:00:19:82.0.0000: 0070:0230 (A4)REP MOVSB 0:00:19:82.0.0000: Registers: 0:00:19:82.0.0000: AX: FF84, BX: 0000, CX: 0001, DX: 005B 0:00:19:82.0.0000: CS: 0070, DS: 0070, ES: FF84, SS: 0000 0:00:19:82 …

What's at F000:0000 in an IBM PC?

Posted on 2015-03-06, 09:49

in PC Emulation

in PC Emulation

I know that F000:0000 to F000:FFFF contain the BIOS. Anyone knows if software expects something to be at F000:0000 to execute? Is there a reserved start of a certain handler there? The same about F800:0000, is there something reserved there? Can this area safely be filled at my own whim with BIOS …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-05, 19:37

in PC Emulation

in PC Emulation

Here's the current debugger log. It's all the commands the CPU executed until I stopped the emulator (it looked like it wasn't booting, according to the INT13 log, it's given an invalid ammount of sectors to load (AH=02h, AL=00h, so read nothing?)).

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-05, 19:11

in PC Emulation

in PC Emulation

It looks like it reads correctly now. It now ends up with a jump to rebooting the boot sector (the JMP to 0070:0000)). Eventually a JMP to 0000:7D00 after the REP MOVSB. 0:00:15:01.1.0000: 0000:7D15 (E2)LOOP 7D00 0:00:15:01.1.0000: Registers: 0:00:15:01.1.0000: AX: 0001, BX: 0B00, CX: 0001, DX: 0100 …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-05, 13:21

in PC Emulation

in PC Emulation

@Qbix: As far as I can see, it's the same as my floppy: cylinder=track side=head The formula is the same, but the track/cylinder and side/head combined into one formula.

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-05, 11:29

in PC Emulation

in PC Emulation

So the formula to find a sector number (0-image size) in an image file is? (Track x Sides x Sectors per track) + (Side x Sectors per track) + (Sector-1) Where for a 1.44MB floppy: Sectors per track = 18 Sides = 2 Is this correct?

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-05, 06:26

in PC Emulation

in PC Emulation

Wouldn't it be (only sectors are 1 based, head and track are 0 based): (1x80x18) + (0x18) + (2-1) = 1440 + 0 + 1 = 1441 (0 based)?

Re: Windows 95 full chip requirements?

Posted on 2015-03-04, 17:39

in PC Emulation

in PC Emulation

I mean, if I would take a motherboard with only IBM PC components, as given by the IBM specs (except for more RAM and a better CPU), enough RAM, a 386DX CPU and 8042 controller with mouse and keyboard connected to it, will Windows 95 run? Or will DOS run and Windows 95 crash because some required …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-04, 13:08

in PC Emulation

in PC Emulation

How does the BIOS know if to run the full POST (Check memory, Show hard disk info, clear screen, boot) or do the final step (boot) only? I currently check for 0x1234. When set it skips the entire emulator BIOS and only reads the boot sector again in the first available drive (floppy 0, floppy 1, …

Re: Windows 95 full chip requirements?

Posted on 2015-03-04, 12:56

in PC Emulation

in PC Emulation

I mean just the bare minimum support to make it run (so VGA card, PIT, PIC, 386DX CPU or higher, PS/2 mouse and/or keyboard). So the basics of an IBM PC with a 386DX or higher CPU and a VGA graphics card. Is there anything more needed to boot? Or will it run with this hardware (emulated)?

Windows 95 full chip requirements?

Posted on 2015-03-04, 11:24

in PC Emulation

in PC Emulation

Is there a list of all chips/hardware needed for windows 95 to run (VGA, CPU, external chips (PIT, PIC etc.))?

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-01, 15:37

in PC Emulation

in PC Emulation

I've fixed the bug in disassembly with my int16 handler. It now goes wrong when the int16 (a copy of the Dosbox interrupt handler) is called (I can't post the disassembly here because it's too big). It executes INT 16h at 0000:7CEA, which calls my own interrupt handler which calls the Dosbox INT16 …

Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-01, 15:20

in PC Emulation

in PC Emulation

That was an error in my disassembly: If it's an FE C2 it means FE /2, which doesn't exist? So it's an #UD? (According to all opcode maps I can find)

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