I have a few questions about the behavior of an 8088 with REP-prefixed string instructions. What is the state of IP when executing a REP STOSB, for example? Does it point at the REP prefix or the STOSB opcode itself? The intel docs say: A repeating string operation can be suspended by an exception …

Sounds like a lot of good improvements. I'd politely suggest some improvements to the user interface. The font you use for the menu system is very hard to read at 1440p and nearly impossible at 4k. A PC user is greeted with "press select" on startup, which isn't very friendly since we have no select …

Are the floppy disk drives set to a appropriate size the BIOS accepts? Like 360K? That's the Floppy A/B without disk type setting in the Manage mounted drives menu. I have them set for 360K, and the DOS disk is a 3.3 diskette. Tried a few other bootable floppies as well. Can you try running it from …

I was getting 601 a lot in my emulator when working on the FDC, yes. I see the A and B indicators go on and off during boot. I'm on Windows 10, 64 bit, using the 64 bit build of UniPCemu

I'm using these ROMs with my own emulator so I'm fairly confident they work. Also the '101' is coming from the POST routine, I believe from one of the PIC, timer or DMA tests. I tried with a CGA and it does do slightly more. 301 640 KB OK 601 ERROR (RESUME = "F1" KEY) hitting F1 at this point does …

Hi superfury, I've been struggling to get UniPCemu running as basic XT. So far I have : A ROM folder with the files BIOSROM.U18.BIN (original filename BIOS_5160_09MAY86_U18_59X7268_62X0890_27256_F800.BIN) BIOSROM.U19.BIN (original filename BIOS_5160_09MAY86_U19_62X0819_68X4370_27256_F000.BIN) VGAROM …

mkarcher wrote on 2022-09-18, 21:01: I don't understand what you mean by "2T4". Maybe you are talking about GFX, index 9, bit 7? Sorry, using the field names from the Ferraro book. It's a bit 7 in the Maximum Scanline Register. I really appreciate you taking the time to reply in such depth.

Great info, and all that makes sense. I am a little puzzled as to why the Maximum Scan Line is set differently in the CGA 320x200 mode (1) vs EGA 320x200 mode (0). Or what the purpose of the '2T4' bit is if it's set for those modes but not mode 13h.

I got things more or less working, I think. One surprising thing in Mode 13h, is that the CRTC is set up for 80 characters and 400 lines instead of the expected 320x200. I don't see any of the bits that would affect the clock enabled. How does the VGA know to double the resolution?

A frame should actually be htotal (converted to pixel clocks, so times 8 or 9 dot clocks) times vtotal (in lines). The lines past horizontal/vertical display end are counted just like normally displayed lines, just not rendering anything at that point. So 800 horizontal clocks times the 500ish …

I seem to recall that "Vertical Retrace" (both the status bit and the optional interrupt) is triggered by the scanline counter reaching Vertical Displayed End. The intention must have been to inform the program "okay now you can write to video memory without worrying about screen tearing". …

superfury wrote on 2022-09-12, 20:40: You can run UniPCemu and dump the VGA state when it's running the retrace test. I'm afraid I haven't had much luck getting UniPCemu to run at all... but say I get it running where would this VGA state dump feature be found?

Hello all, I've been writing yet another hobby IBM PC emulator, and several posts here have been incredibly useful resources on CGA timings, etc. I was a bit hesitant to ask but this seems like the place to get the answer, so, here's my first post. I've encountered a bit of a puzzling roadblock …