Downgrading the Plexus P20 emulator to Visual C++ 2003

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I ended up falling down the rabbit hole of the P20. For those who don’t know here you go:

This is great, not ONE but TWO 68010 processors! 2MB of RAM, and SYSV Unix!

NEAT!

Adrian has (had he’s donating it) so the odds of people playing with it, are slim to none. But no, there are not ONE but two emulators!

There is a QEMU based one, and a MUSAHI based one.

I had thought about trying to take a look at the SCSI handling as the system uses one of those funky MFM disk shims with a SCSI ‘like’ interface bus.. It has an interesting layout with the first block to explain the disk to the controller and the system, along with the disk partitions/slice layout. Very early 1980’s stuff.

Anyways despite all these years, I’m kinda terrible with Xcode, so I thought using Visual Studio to debug would be the way to go. And whoa… I had a copy of 2010 handy as I was having internet issues, and yeah it’s more C89 than C99.

And then there was this fun thing while trying to do an optimised build:

c:\proj\plexus_p20\musashi\m68kfpu.c(134) : fatal error C1001: INTERNAL COMPILER ERROR (compiler file 'f:\vs70builds\6030\vc\Compiler\Utc\src\P2\main.c', line 148)

Nothing like crashing the compiler 🙁

Thankfully you can simply turn off optimizations in the various parts of the source that crash.The Plexus neither has and I think pre-dates the 68881/68882 so the FPU emulation really doesn’t matter, just simply add

pragma optimize("", off)

at the start of the file, and turn it back on at the end. Yay!

Visual C++ 2003!

So yeah that was pretty fun.

Oh I should add there is a WASM version, so the ultimate for tourists, you don’t even have to install anything! Super cool!

I thought I’d try to make a slight improvement since I expect people to use old machines, so I amputated ansicon, and drive it directly! So, no DLL injection or anything else weird, to try to prevent antivirus software from freaking out.

It’s enough for vi to work at least!

Although I should probably detect Windows 10, since it has the ability to detect and drive ANSI codes on it’s own.

Anyways for anyone wanting to check it out on Windows here is the repo with the first release:

https://github.com/neozeed/plexus_p20-vc2003

Don’t forget you’ll need ROMs and a Disk image.

Oh C compiler is installed, and I believe Fortran as well! The ‘catch’ is there currently is no good way to move data into the VM. Pasting into the console gets dropped chars, and it’s just impossible. uuencode to the system OUT however works great.

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