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Re: Interesting VM86 entering issue

Potentially-silly question, but what is the effective operand size of the IRET? If it's in a 16-bit segment you'd need the operand-size override. Without it, that could explain the loading-CS-as-a-descriptor-rather-than-an-offset behavior. The Intel manuals suggest it's all one operation. As far as …

Re: Open Source i386 BIOSes?

I'm using SeaBIOS in my emulator, but if I remember correctly it relies on the remapping support in the chipset to decompress itself to RAM. Edit: IIRC the *legacy* Bochs BIOS doesn't rely on this, and is only 64K so it fits in the F000 segment.

Re: x86 PDE/PTE dirty/accessed bit updating?

The Intel SDM says: Whenever the processor uses a paging-structure entry as part of linear-address translation, it sets the accessed flag in that entry (if it is not already set).Whenever there is a write to a linear address, the processor sets the dirty flag (if it is not already set) in the paging …

Re: Programming PC Emulator Getting Started Questions

The datasheets have all the commands/parameters/etc listed, and are a pretty good resource. Can also consult many of the emulators out there, although not all of them are "correct". Cycle accuracy definitely isn't a requirement except if you want to run some very picky demos. If I recall correctly, …

Re: Programming PC Emulator Getting Started Questions

There's a few of us doing PC emulators in various communities, I lurk here and on the emudev discord. A few public domain BIOSes exist for the PC/XT, you can find some of them here: http://minuszerodegrees.net/xt_clone_bios/xt_clone_bios.htm. I've personally used this one: https://www.phatcode.net/ …

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

VIDE-CDD seems to work fine for me after a disc swap. Two ATA channels, CD-ROM is on primary slave. FWIW it's the same on the secondary channel. Trace: [ 235.7322] T/i8259_PIC: PIC 1 mask 0x8F [ 235.7324] T/HW::HDC: ATA write drive select 0xB0 (drive 1) [ 235.7337] T/HW::HDC: ATA read status …

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

Here's a trace from my emulator for a "dir" command after swapping discs. The first command is the "test unit ready", and the final command is the re-reading of the TOC. [ 10.8132] T/HW::HDC: ATA 0/1 write control register <- 0x08 [ 10.8137] T/HW::HDC: ATA write drive select 0xB0 (drive 1) [ 10.8142 …

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

To be honest, that confused me a bit too. I guess the driver has to work out which device caused the interrupt by checking the status bits. However, I still suspect your problem is due to not erroring out on the test unit status command. Edit: Should mention, if you're firing the interrupt, probably …

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

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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