Emulating Homebrew Single-Board Computers with MAME

[@MikeyN6IL]

I was fully aware of Grant Searle’s single board computer and FPGA based projects, but I had no idea that these boards were in MAME. The MAME debugger is very good and I have done lots of debugging with it. It is easier to use with systems that have a flat memory map. Things get a lot more complex on systems that have a MMU or bank switching. I have used the CPU trace feature many many times. One of the best parts of the debugger is that you can see and manipulate the registers and many times internal states of any attached peripherals such as PIA/VIA, UARTS, FDC, etc. Another powerful feature which is normally not present in Monitor programs is memory watch points. Again thanks for the excellent video!

[@thirstyCactus]

Neat! I would love to see how to emulate custom hardware, like the 6522 chip on your 6502 SBC. I did a bit of research, but hit a wall trying to find documentation on making custom MAME systems for hardware emulation.

[@joelavcoco]

Yes, this is the kind of information I'd love to have as well. The MM/1 is a computer designed by TRS-80 Color Computer enthusiasts after Tandy pulled the plug on the CoCo 3, as a CoCo 4 candidate. Maybe a few hundred were ever made. There is no emulator, but almost every component in the machine exists in some form or another in emulations of other machines -- just not put together in the same place. If you trawl through the MAME codebase, I'm almost certain you'll find emulation of the 6522. So the remaining question is whether the different machines are standardized enough in their code so that you can pull a chip from this machine and stick it into that one. I'm fairly sure, based on my limited poking around, that there aren't 2 dozen different implementations of, say, a 6821, or an NEC 765. Maybe these extremely simple SBC emulations are a good way to learn about the MAME code and figure out how to glue the different emulated chips together to make something new.

[@tgopaul]

Hi Jeff thanks for the mame demo. On Windows 10 I couldn’t get mame 0.262 to load your combined rom image from the GUI interface because of an incorrect checksum. Loading mame from powershell console ./mame gs6809 allows pressing enter to ignore the checksum error. Also checksum bypass works from the command line: mame gs6809 Your board is similar to the mame defined machine from Grant Searle. I am new to mame. I got this far. I downloaded your combined.hex file and converted it from Intel hex to .bin I named it gs6809.bin then zipped it to be gs6809.zip and placed it in the rom subfolder of mame. Launching it from the command line with mame gs6809 worked after pressing anykey to bypass the checksum warning. A fun video would be demonstration a simple project on both on physical rom flashing and emulated the same in mame. It might help clarify the connection between hardware and emulation. I’ll try running through Heathkit ET-3400 emulation with the expansion ROM images. I also have an ET-3400 that I wired in 1980. I have’t built the expansion unit for it yet.

[@derekchristenson5711]

I had no idea that MAME could do that. Cool!

[@G7VFY]

Have you tried the Australian TEC-1G Computer (There is a similar version call the Southern Cross.) G7VFY

[@ka7znm]

Why did your perfect squares demo miss 25? or did I miss it...?

[@ka7znm]

missed 36 too.

[@jefftranter]

The program has a flaw in it. Depending on the version of BASIC used, the square root of 25, for example, is not represented exactly as 5 and the program fails to report it. The flaw can be fixed with a slightly more complex program.

[@ka7znm]

just for sanity, I just tried same code in bwbasic and it worked fine... but I will play with MAME also... thank you for the intro. I had seen some of the old CP/M machines in the list but had not had any luck making them work. Studying the ROMs for Donkey Kong was good fun though.