After my success with getting Northstar DOS to boot on my SOL-20, I decided to try my luck with CP/M.

I gathered what I considered to be all the components I needed. A variety of Northstar CP/M 2.2 double density disk images, and SOL-20 specific DBOOT and CBIOS assembler files.

First I converted the assembler files into binary files for patching with a HEX editor, then I loaded various versions of the disk images into the editor and looked around for the places that needed to be patched. Unlike Northstar DOS images the structure of the CP/M images seemed a lot more complex and open to variation.

Finally after some struggling, I was able to produce 3 disk images for testing. 24k and 52K lifeboat versions of Northstar CP/M, and a third that I didn’t think would be successful at all, but I thought I’d try anyway, a Xitan distribution of CP/M. I believe the Xitan version is for a 3rd part Z80 card for the Northstar.

Using Dave Dunfield’s NST utilities and Corey Cohen’s SOL-20 specific NST stub, I was quickly able to make 3 boot disks. To my surprise neither of the Lifeboat versions worked. I was able to see the boot message, but the keyboard was unresponsive. The Xitan version however booted first time, although many of the .COM programs didn’t work. I’m assuming this is because that were built specifically for the Z80 processor and not the 8080 processor found in the SOL-20 and original Northstar Horizon.

I removed all the programs that didn’t work and saved the resultant disk back as a master boot disk image.

I wish I felt more confident about the process of patching CP/M. Unlike the patching of Northstar DOS, it seemed a lot more hit or miss. I am happy that I was able to get it working though, and have been using CP/M without too much trouble on my SOL-20 for the past few days.

For those wanting a little more insight into the entire process, please look at my writeup for booting Northstar DOS on my SOL-20. The process is almost identical.

All the files needed to get your SOL-20 system running either CP/M or Northstar DOS are available on my FTP site.

Good luck.

neoncluster.com