Sunday, March 15, 2020

NitrOS9 on (an emulated) CMS 9619

I have been working on some ideas to expand my CMS 9619 SBC. I thought an SD card interface would be a nice option, but I didn't want to use any modern microcontrollers or FPGAs. I had a circuit pretty much worked out, but then thought a Compact Flash card would work better for 8 bit transfers.

While working on a circuit to interface with the MC6821, I realized that I already have a nice RS232 connection to the computer, why not use it? So, I wrote a 6809 assembly tool for the CMS 9619 debugger (debug19) to download blocks of data using the zmodem protocol.

This was working so well, that I figured I could use it to boot load NitrOS-9 on the board. Since I am moving soon, my computers are all packed away, but I couldn't wait to try it. I made some changes to sbc09, a simple 6809 emulator, to emulate the CMS 9619. Here is a video of the boot process to NitrOS9 all the way to the shell:

And it works! I need to finish a real zmodem driver to get it running other commands on the disk image though. Once I move, I can test it out on a real computer.

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