Musashi: Motorola 680x0 emulator written in C

by doener • 7 months ago

124 14 7 months ago

kazinator• 7 months ago

I made one a 68010 emulator in C in 1994.

For the opcode dispatch, I made a file which consisted of regex and name pairs. The regexes matched strings of 0s and 1s: the bit patterns of the opcode space. The names mapped these to C functions. A script processed the file, generating the dispatch switch.

I seem to remember that on a 66 MHz 486 DX2 box running Linux, the thing was emulating about half a million instructions per second.

Code: totally lost to the sands of time.

self_awareness3• 7 months ago

FYI: MIT licensed

self_awareness3• 7 months ago

Is it wrong? Who the heck downvotes this?

debo_• 7 months ago

username checks out

rcarmo2• 7 months ago

I took a look at this during my holiday break (where I was hacking BasiliskII to do JIT emulation on ARM), and it’s quite neat but, IIRC, wasn’t enough of a speed up over the existing emulator.

dukoid• 7 months ago

I'd expect the main advantages to be portability and maintainability?

rcarmo2• 7 months ago

I was looking for more speed on ARM devices.

kstenerud• 7 months ago

Wow! Wasn't expecting this to be on HN.

So here's the backstory:

I'd just graduated from BCIT a year before. A friend invited me to visit Japan, so I got a working holiday visa, hopped on a plane, and there I was in a 1K apartment with 2 other people. I had one whole square meter of floor space for my computer (which I'd packed with me) and a donated monitor.

While looking for tech work, I fiddled around with MAME, doing small fixes to drivers and such, but I'd always had a love for the 68000 chip (from my Amiga days), so I looked at what MAME was doing and saw that its 68k emulator was written in assembler.

So I set a goal: Can I outperform the current assembler core with one written in portable C? Spoiler: Yes.

I spent 2 months sitting Buddha-like on the tiny square of floor in between job interviews, writing (and leveraging MAME's debugger). My proudest moment was when I finally saw the title screen for Rastan Saga pop up! (of course it crashed on launch, but still)

I named it Musashi, after Shinmen Musashi-no-Kami Fujiwara no Harunobu (新免武蔵守藤原玄信), commonly known as Miyamoto Musashi, who wrote the Book of Five Rings - a book that had a huge effect on me.

jacquesm2• 7 months ago

Great story. It is interesting how being stranded in some place with a computer and some skills always results in the most fantastic projects.

lelanthran• 7 months ago

Great story. It is interesting how being stranded in some place with a computer and some skills always results in the most fantastic projects.

TLDR: IME, solitude is required for clear thinking.

-----------------------------------

Long ago, I used to drive 600km (one-way) twice a month . Kept it up for 4 years or so. As I drive with the radio off, I had much time alone with my thoughts.

Now, I wonder if always reading is having a negative effect: we're constantly bombarded with content all the time, and even though I never doomscroll (no tiktok account, no FB account, no instagram, etc), I think sometimes that enforced solitude might do wonders for my problem-solving.

I wonder how people who are on all those social networks ever find time to just ruminate.

ale42• 7 months ago

Very true. Had a somewhat similar experience while being offline in trains for some hours at a time.

matwood• 7 months ago

Also the book simply named “Musashi” is amazing and tells the ‘story’ of his life. It has arguably the best ending of any book I’ve ever read where the lead up builds for 1000+ pages ending in a crescendo.

Musashi: Motorola 680x0 emulator written in C

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