A cycle-accurate IBM PC emulator in your web browser | Hacker News Reader

A cycle-accurate IBM PC emulator in your web browser

martypc.net

158 pointsGloriousCow25 comments

MartyPC brings cycle-accurate IBM PC emulation to your web browser.

Run Area 5150 at 60fps on your phone!

Almost every feature from the desktop version is present if practical:

- View the realtime state of nearly every component of the system. - View live disassembly of CPU instructions. - Edit registers and memory. - Slow down or speed up the system. - Peek on how games draw their graphics with the Memory Visualizer.

I've been using MartyPC for a few years and except for emulating glitches in hardware which depend on the manufacturer, date of manufacture or even temperature, it is getting harder to find cycle accurate tricks that MartyPC can't emulate perfectly (believe me, we've been trying).

The whole thing is a marvel of software engineering!

What is remarkable is that the author (GloriousCow) doesn't complain that people are ripping off his code and ideas, but that more people haven't used his learnings to create other cycle accurate emulators for the PC.

Temperature? Really? How does that work?

If you program a register at a moment and in a way that causes two signals to "collide", the result effectively depends on transistor behavior. That in turn can be temperature dependent.

For an example on the PC see https://int10h.org/blog/2023/03/cga-6845-crtc-phantom-vsync-...

Thanks. Transistor level race conditions will keep me up at night.

Amazing link. Thanks for sharing.

Where can I find more writeups like this?

That was a fun rabbit hole. My first computer (8-bit, 4k RAM, 0.8 Mhz) had a video chip related to that 6845, the 6847, which was (sadly) a somewhat lower cost, less capable, less interesting chip.

Pretty incredible!

I’m on mobile right now so I can only comment on the demo that runs automatically, which I understand isn’t the _point_. :)

More about the demo: https://www.vogons.org/viewtopic.php?t=89435

(For those unfamiliar with “demo” in this context, see https://en.m.wikipedia.org/wiki/Demoscene)

I look forward to checking out the features you mention on a proper computer.

I loved it when the Doom floating head demon guy came up. Right when y'all were about to ask "...but can it run Doom?"

Thanks for pointing people to Area 5150. Context for others: This, and its predecessor 8088 MPH, uses every single trick in the book and many not written down anywhere to squeeze that kind of performance out of a real 1981 IBM PC 5150 with IBM CGA card. Thus they only run correctly on that specific hardware, not a clone computer or card. "Regular" software emulators also have a tough time. Showing off MartyPC with Area 5150 is thus two technical feats combined into one.

Can you imagine sending an Area 5150 disk back in time to 1981?

You’d be fussing around trying to find enough RAM expansion cards to get your system to 640K (including hot patching the BIOS since it had a bug that it could only get to 544K).

Ought to be enough for anyone.

640 KB in 1981 was more expensive than 640 GB today.

That was only the first 64k motherboard. ( Five slots only ). Fixed with the PC that came out less than two years later. My brothers machine only had 384k, and it was more than enough. Only three years after, I built 10Mhz XT w/ a V20 640k running Xenix.

One of my neighbours in Sydney sold a board he made in his garage, that gave you an extra ten slots, which I filled with way too much RAM. Sort of like a homebrewed 5161, before the 5161 existed.

That's kind of neat. Did he just extend the bus in a "raw" fashion or put buffers on it? (The downside of the 5161 was any memory device in the 5161 had an extra wait state thanks to the speed of the buffers, which were necessary to deal with the capacitance on the cable to the expansion unit.)

They were buffered, from my poor memory. So was slower when you exceeded mainboard memory, but you could load entire tapes into memory, which let you do things no one else could. Faster processing than disk/tape access.

If I had seen this back in the day, I might have given up on programming out of sheer awe!

Wow that's amazing. I sometimes play NES emulated games, which are (due to hardware limitations) using some tricks while displaying larger mobs, to show a few sprites instead of one (and using monitor synch to quickly switch the sprites in between switching to another scanline). This however renders as blinking in my emulator.

I can only imagine that this demo was doing similar tricks to "push the limits" on CGA.

Also, I remember my i386-33SX playing full 4 channel music on the PC Speaker in the game "Pinball Fantasies". This was state-of-the-art (also not working properly on DOSBox emulator nowadays)

This appeared on the fp the same day i spent 15 hours trying to get various old/weird OSes installed. Xerox Star (viewpoint), os/2 warp 4, serenityos, debian 9, and where is freebsd 2.2 disc 2, might i ask?

commenting for posterity, and to say the web emulator is very slick, i have some dos diskettes to try out.

I miss Notacon and Jason Scott's Demoscene parties.

Some of my best hacker/nerd friends I met at notacon. It had a vibe that no other con I’ve been to has had.

That demo was pretty mesmerizing!

truly epic!

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