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Okay, this is a bit of a weird one.

I am looking for an emulator for a 6502 (well, 65C102) second processor. Not the I/O processor, just the second processor. Has anyone heard of this?

What I want to do is to run compiler tests, so I want to be able to load a program into the second processor and then run it once, with the stub MOS hooked up to a very very simple emulated I/O processor (just supporting stuff like file access and input/output streams mapped to host stdin/stdout, no VDU emulation or anything like that). That way I can effectively run a simple BBC MOS program in a way which is compatible with my Unix-based build system.

It should be relatively simple to bodge one together via lib6502, but I'd rather not have to. Has anyone ever heard of such a thing?

I started to hack something very much like this together out of the 'run6502' demo supplied with 'lib6502' - I took the Tube client ROM from Acorn's 65Tube emulator for RISC OS and started implementing the special opcodes, so I could have '65Tube for Unix', in effect.

I think the approach is workable but I got fed up with the fiddly details and stopped. If no one has anything better I could push my code up to github if you're interested in maybe making some enhancements.

I would like to see something like this myself, it would be nice for testing things like my PLASMA port where all you need is basic 'teletype' I/O.

ETA: Sorry, reading/writing this on phone and didn't see your mention of lib6502, so perhaps not very helpful. But just possibly what I already bodged together would be good enough for your needs without much/any extra work.

I assume that you know BeebEm has selectable 65c102 second processor emulation. I don't know how accessible the source code is but it may be a usable start?

FWIW, I just slightly tidied up my lib6502-based hack and pushed it to github. It's at https://github.com/ZornsLemma/lib6502-sf.git.

Here's a brief demonstration... You'll need to get Code064.rom and (for this demonstration only) HiBasic430 yourself - they're not in the repository. You can get them from mdfs.net at http://mdfs.net/Software/Tube/6502/ and http://mdfs.net/System/ROMs/Language/ respectively.



Don't be surprised if anything more sophisticated fails to work, but if you have any questions/suggestions I'll see what I can do... (Patches/forks also welcome, of course!)

Great! I've a feeling I tried to do something like this in the past and got bogged down.

hjalfi wrote:I am looking for an emulator for a 6502 (well, 65C102) second processor. Not the I/O processor, just the second processor. Has anyone heard of this?
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Has anyone ever heard of such a thing?

Yes, it's called 65Tube.
I also wrote a version entirely in BASIC to demonstrate how to do it, 65TubeEm which is the same fundamental structure as 6809Tube and PDPTube.

Ha. Went away on holiday and hacked one up myself --- knew I should have checked the forums while I was away...

Mine's at https://github.com/davidgiven/cowgol/tr ... u/bbctube; there's just enough functionality there to run HiBasic. Unlike run6502 it doesn't need an OS ROM, as it emulates the OS layer directly. It's unfinished as I haven't done any file I/O calls yet but they'd be easy to add.

One oddity is that while everything else seems to work, entering a program ends up with mangled line numbers (or missing lines completely). Does HiBasic use decimal maths, by any chance? Could I be corrupting the decimal flag?

cZ80Tube looks really interesting (I can't use the BBC Basic ones), but sadly doesn't build out-of-the-box on modern machines --- looks like it's not including any of the required header files. I may have a look later, but I don't have time to fix it myself right now.

I think the corrupt line numbers is caused by a lib6502 bug - even the latest upstream may not have the fix (I submitted it but I think Ian was busy). You might want to get the lib6502 from my github repo and build your code against that - it has a fix in, and I believe my version of lib6502 will pass Klaus Dormann's test suite.

I'm afraid I can't remember what the bug was, but if you diff lib6502.[ch] from my repo with upstream it will probably be fairly obvious.

Yes, that solves it --- thanks! As I want this for compiler tests, having correct emulation is kinda important...

One (related) question: HiBasic's HIMEM is reported as &8000. This seems wrong --- shouldn't it be &B800? I can see it using OSBYTE &83 and &84 to ask for the HWM and HIMEM, but of course these apply to the I/O processor only. The New Advanced User's Guide even mentions that on a second processor, OSBYTE &84 does not return HIMEM.

My understanding was that programs which have claimed the Tube (which is implicit in my emulator) get access to the entire address space from &0400 to &F800. HiBasic, having loaded at &B800, doesn't need to contact the OS to find out where its workspace is. So why is it using the wrong value?