Re: UniPCemu's Dosbox-bases CD-ROM swap issues?

Posted on 2019-07-10, 09:29

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by Stenzek

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Hmm. Not sure exactly, I have it triggering when new media is "inserted". I recall having similar issues (it not showing the new directory), not sure if this was the only thing which fixed it. At least with the OAKCDROM driver I'm using, the "test unit ready" command which is sent after the DIR …

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Re: UniPCemu's Dosbox-bases CD-ROM swap issues?

Posted on 2019-07-10, 06:08

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by Stenzek

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Are you raising the interrupt when the media is changed?

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Re: Linux 0.01 strange behaviour with ATA hard drives?

Posted on 2019-06-26, 10:01

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by Stenzek

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So, looking at QEMU's source code, writing to the block registers(those registers that went wrong with UniPCemu) for all registers but the drive/head and command/status registers writes to both master and slave registers, while reading from them only reads from the currently selected drive? That …

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Re: Pentium VME IR bitmap?

Posted on 2019-06-19, 01:15

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by Stenzek

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I *think* qemm might use it, but I can't remember for sure.

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Re: Pentium VME IR bitmap?

Posted on 2019-06-17, 14:28

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by Stenzek

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I used these programs when testing my implementation, might be helpful: http://www.rcollins.org/articles/vme1/

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Re: x86 #GP/#SS fault in modern operating systems?

Posted on 2019-05-29, 01:39

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by Stenzek

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I don't see any need to simulate the effects, user-mode programs should not be able to change the IDT, so raising a signal seems appropriate.

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Re: x86 #GP/#SS fault in modern operating systems?

Posted on 2019-05-28, 06:06

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by Stenzek

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Is the #GP/#SS fault used in any case with modern operating systems, but for other effects than terminating the offending program/driver/OS? Absolutely used in paging and memory allocation. A #GP is raised if the program tries to access memory that isn't currently allocated/loading in. The OS will …

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Re: x86 #GP/#SS fault in modern operating systems?

Posted on 2019-05-28, 02:30

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by Stenzek

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As far as I'm aware, not really, modern OS's just use a flat address space. Even things like stack overflows are checked via the paging unit. The FS/GS segments can be used for thread-local or process-local storage (basically a base pointer which is indexed). Swapping in/out is also done via paging. …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-05-09, 01:27

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by Stenzek

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Are you sure that emm386 uses 16-bit interrupt gates? Using the emm386.exe provided with WFW 3.11, for the DOS interrupts at least, I'm seeing an invalid (type 0) descriptor, which results in a #GPF, which is a 32-bit interrupt gate. External interrupts (e.g. IRQ0) are a direct 32-bit gate. edit: if …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-05-06, 06:38

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by Stenzek

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superfury wrote: Doesn't that cause troubles when using IRETD to return to the V86 task? Since IRETD always pops DWORDS? I'd think an os which used 16-bit gates would use iret, and if it used 32-bit gates, iretd. edit: FWIW, Win95 seems to use 32-bit gates and IRETD.

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-05-06, 02:59

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by Stenzek

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I have it pushing words/dwords depending on if it's a 16-bit or 32-bit task/interrupt gate.

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-05-06, 02:19

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by Stenzek

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Anyone knows what effect the operand size has on 16-bit segment register push operations? Are they pushed zero-extended to 32-bits? In my emulator: push segreg -> 16-bit, write 2 bytes, 32-bit, write 4 bytes, sign-extended. Bochs writes 2 of the 4 bytes, but decrements (E)SP by 4. Wrote a quick …

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Re: x86 opcodes 0FB7 and 0FBF 16-bit?

Posted on 2019-04-08, 13:43

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by Stenzek

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As far as I can tell, 0FB6 extends 8-bits to the operand size, 0FB7 is always 16->32-bit. As the second operand of 0FB7 is 16-bit, it wouldn't make sense to zero-extend 16-bits to 16-bits. Edit: Seems my implementation (and bochs) differs. 0FB7 with a 16-bit operand size is essentially a 16->16 MOV …

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Re: x86 NT(Nested Task) flag vs VM flag?

Posted on 2019-03-26, 07:34

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by Stenzek

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I think what you're describing (handling software interrupts in DOS) is kind-of what the V86 Mode Extensions were added for. It allows you to specify a bitmap of interrupts which will not trap to the V86 monitor, instead branching to the location stored in the IVT (while remaining in V86 mode, even …

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Re: x86 NT(Nested Task) flag vs VM flag?

Posted on 2019-03-26, 06:12

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by Stenzek

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As far as I understand things, that's a limitation of the V86 mode. Plenty of other ways to exit V86 mode, I guess you could for example have a software interrupt which goes to a task gate.

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Re: x86 NT(Nested Task) flag vs VM flag?

Posted on 2019-03-25, 00:10

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by Stenzek

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VM flag has precedence over the NT flag according to the Intel manual. I'm assuming real hardware functions the same, but you could always write a test to confirm.

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Re: What CPU state is reversed/restored when a fault occurs?

Posted on 2019-03-20, 02:23

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by Stenzek

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I tried to break instructions up into transactions, with read/modify/write/update parts. State such as flags changes are performed as part of the "update" stage. So for example if a page was not writable, the read/modify would succeed, exception would be raised on the write, which jmp's back to the …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-03-18, 00:11

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by Stenzek

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Hmm, I also had the delayed text input issue at one point. Not sure if it's related, but it went away after I'd rewritten my keyboard controller emulation with the serial timing (so reading the port twice would give the same value, until the next scancode is filled).

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Re: What CPU state is reversed/restored when a fault occurs?

Posted on 2019-03-18, 00:09

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by Stenzek

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I only save/restore ESP/EIP in my emulator on exception. For the other registers which could leave the CPU in an unrecoverable state, the fault condition is checked before modifying them.

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Re: UniPCemu Windows 95/NT progress and issues

Posted on 2019-03-03, 01:18

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by Stenzek

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It definitely doesn't have to be super accurate, all the timings in my emulator are approximate (but deterministic). You definitely should be getting identify commands. FWIW, the order of commands I'm seeing with a single HDD attached for NT3.5: - Probe PCI config space (I'm emulating the PIIX). - …

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