[v1.1] MECB 1MB ROM Expansion Card

[epaell]

OK, so I lied when I said I would leave it at that ... I was also curious if I could get a hypothetical MECB board to work. In this instance I added an MECB 68008 to the list



Again, purely academic, but in this instance it turned out being really useful to work out how to get zBug to work on this system.

[epaell]

Also added Tutor monitor (which is one of my favourite monitors for the 68000) and enhanced BASIC to the mix ... just for laughs.

[Editor]

Also added Tutor monitor (which is one of my favourite monitors for the 68000) and enhanced BASIC to the mix ... just for laughs.

Awesome! It looks like I really need to get on with finalising the design for my MECB 68008 CPU Card.

I guess a software emulator is always good for reving up a hardware guy (who isn't keen on software emulation), to get on with making some hardware! LOL

[epaell]

LOL, Bring it on!

Something that I realised once I started this adventure (which I previously knew but forgot over the years) was that the 68000 vectors are at the low end of the memory map. That in itself is not an issue but because numerous SBCs did unusual things to allow modification of the vectors (e.g. remapping the first eight bytes of ROM to the lowest part of the memory map and then having RAM at the low end) it makes porting software a real pain - I guess it doesn’t help that there is 1KB worth of vectors! Anyway, I hacked it to some degree in the software but it is far from complete. The other thing that bit me was the mapping of the ACIA which on the 68000 has the registers on even bytes (this was a bit easier to overcome with the 68008 because it has an A0 line).

[bugeyedcreepy]

In case anyone else wants to mess with MAME I've added my updates to GitHub:

https://github.com/epaell/MECB/tree/main/MAME

You, my friend, are a Legend!!

[djrm]

In case anyone else wants to mess with MAME I've added my updates to GitHub:

Hi epaell, Just last week I was wondering how I could create a MAME configuration to simulate my old 6809 system. I have no experience of MAME and my search led nowhere productive. I'm very happy to find your ready made system and shall be trying it shortly and maybee editing it to suit my own board layout.

Best regards, David.

[epaell]

That's great to hear - it's one of the reasons I thought I'd post my example in case it helped others. It's still very system dependent in terms of getting up and running and I'd have to admit I'm struggling with a new laptop that I just got because it has a different processor in it and somehow that is making it all so much harder (despite it having the same operating system as my old laptop).

[djrm]

That's great to hear - it's one of the reasons I thought I'd post my example in case it helped others.

Ive never used MAME before - or so I thought. I've just installed it (flatpack) only to find it was already installed (i'd forgotten - showing my age). I used it to explore some old systems at some point in the past. Now I have to see ho to import your work. i've cloned your GH repo for a start. A new adventure beginning - or is it a rabbit hole. I'm glad of your example, i tried reading ho to make a config from scratch but it seemed a steep learning curve.

[epaell]

Ha ha, I was the same - I think I had two installations on my old laptop - one where I was messing with games and another where I wanted to emulate a particular machine ... and then this recent version where I wanted to create something new.

I'd have to admit that there are still some things that I haven't quite got my head around e.g. I would've thought it should be simple enough to add a PIA and the attached sound device and I so an example of how to do this in one of the other "machines" but when I try to do the same it just doesn't want to compile and the errors are really cryptic. I based my example on one that was already in the home-brew section of MAME (it felt like it was easier to tweak an existing system than starting from scratch) but all of the examples there were quite simple and didn't really push the capabilities of MAME much.

[djrm]

By installing a third instance I can now compile your machines and even run them after a fashion. Problems I have seen include a bad checksum in the 6809 rom (fixed cs but no new sha value supplied yet) , and a missing 6502 rom (biosev.rom) I have not managed to get a serial console working in a meaningful way, the output looks to have the wrong baud rate or something similar. I see an alternative method to use a socket connection and I shall try it to see if its any better but I'm doubtful. Anyway its been a successful trip so far and I should be a lot nearer to being able to making my own configuration soon. I want to have a simulated system with 6522 and LCD somehow but my own serial monitor with 6551 ACIA would be a good start (or even 6850 at my uart address).