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A project log for rosco_m68k

A full-featured Motorola 68k retro computer, starring a 68010 running at 8MHz

Ross BamfordRoss Bamford 05/07/2020 at 18:290 Comments

Whew, it's been a busy couple of weeks here on the project, with lots going on and lots to update, so I'm going to give a quick rundown here of the main developments that have been happening. 

Tindie launch - response has been amazing!

It's almost a month since the rosco_m68k launched on Tindie, and I've been amazed by the response! I honestly wouldn't have believed back when I started this project that anyone else would be particularly interested in it, but it seems like it's going to be a modest hit, and I'm super grateful to everyone who's ordered one, or added them to their wish lists - thank you all so much!

Rest assured that the money from sales will be put to good use designing new expansions for the rosco_m68k, expanding the software, and generally making it better all the time. A V9958 video board is already in the works (more on that later!), a RAM expansion has launched today and there's a new local-bus / backplane board coming real soon (just needs one more spin through manufacturing to correct some minor issues).

Once again, huge thanks to everyone who's already built their very own brand new, really-old computer, and if you haven't got yours yet but would like one, you can find it available now on Tindie.

Community is growing!

Now the rosco_m68k is "out there" and people have jumped on board, it's been great to see a bit of a community growing around it. It's truly awesome getting together with people and hearing their plans and ideas for the computer, things they want to try and new stuff they want to make.  

We're using Discord as a place to meet, and it's great to see people there who have been long-time friends of the project since the breadboard days here on Hackaday as well as new faces. If you'd like to get involved we'd love to say hi - find our server at https://discord.gg/zGUB7R8 .

The computer has an emulator!

Speaking of community, @Micko_mame joined Discord after building his rosco_m68k kit, and hasn't stopped amazing me since with the things he's doing with software. As a developer of the MAME emulator, Micko knows his way around the source of that project, as he demonstrated with a real mic-drop moment when he posted a picture of the rosco_m68k firmware and examples running in the emulator. 

I cannot understate how awesome this is, debugging on a single-board computer with no kernel and only serial IO can be a challenge at times. Micko's MAME fork will really speed up the software development, both by reducing the compile-run loop time and allow single step debugging in a nice window, as seen in the shot above.

This really came into it's own recently when I was writing the initial bootstrap test code for the V9958 - writing to registers and especially to VRAM can be a bit challenging on that chip and it's hard to know if the code actually does what you think it does. Of course MAME supports the V9958, and Micko did the necessary wiring to expose it to the rosco_m68k target, and we were off to the races. Just being able to peek at VRAM and the V9958's registers saved a ton of debug time.

You can find Micko's MAME work in his fork on GitHub and trust me, it's well worth checking out - it supports RC2014 too if Z80 is more your thing than m68k :)

We are running MicroPython(!)

Another of Micko's mic-drop moments was when he announced (pretty much on day one!) that he'd gotten MicroPython running on the rosco_m68k! This is awesome on so many levels - I mean, it's a 68k running Python for one thing, but it also could open the door to a really nice machine monitor, written in python (with some assembly/C glue of course) and driven from the Python REPL. I'm super excited to start playing with it (I've sadly been head-down packing orders for shipping, frantically sourcing components and designing the V9958 expansion, but I'm going to be getting back to some software this weekend).

To get this running, Micko also had to do a minimal port of Newlib, no small feat when there's no OS, no memory management, and only serial IO.

Check out the code here: https://github.com/mmicko/micropython (on the mc68000 branch).

Larger Roms & V9958

@RTS4E75 (geddit?) also joined in on Discord, and though he's been waiting a while for components and free time to build his computer, he's already got a lot of great ideas. 

For a start, he immediately noticed I'd done something a bit silly when designing the revision 1 PCB, and failed to connect some address lines that would have let the rosco_m68k easily support larger ROMs that have the same footprint as the 16K that's fitted as standard. My bad, but once he's fully up and running with his board he's going to prove out the idea, and if it works I'll be fixing the problem in a future board revision. The current thinking is that 64KB total should be doable without any real design changes, and maybe even larger with a jumper or two to change how some of the lines are connected.

Along with long-time friend of the project @henk.gooijen, RTS4E75 has also been involved in a lot of the conversations about the next hardware steps, especially the design of the V9958 and how it'll interface to external displays. I'm really looking forward to getting the V9958 on a board and really playing with it - right now I have a breadboard(!) circuit with barely working video RAM (an old Amiga expansion hacked in as the DRAMs I ordered haven't turned up yet :( ) but there's still the MAME emulation I talked about earlier so it won't stop the work on the software side.

It's a known fact that stuff designed with input from people is always better than stuff designed in isolation, so I'm really lucky to have everyone involved :)

Conclusion

So, as I said, it's a busy time on the project, but I'm loving every minute of it, and I can't wait to build the next thing. There are so many ideas being floated at the moment (including floppy/HDD storage, ROM monitors / debuggers, and all kinds of other things) that I'm more excited than ever about the future of the project. 

And, once again, thanks to all who've already built their rosco_m68k, as well as anyone who is thinking about getting one - you're all totally awesome!

(Both images posted in this log came from and remain property of Micko)

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