@shpuld the devkit install went perfectly smoothly, but there were two sticking points (well three if you include poor documentation.) Installing KOS was just running a few scripts and it all built. Which was a miracle as I have never seen this much GNU dev utilities built from source without an error killing it partway.

The two problems are: 1. there's a tool for sending code to the dreamcast. The documentation says to use it. It's not included for some reason and it was kind of hard to find, the first version I found was old and didn't compile. I found an updated version on Github thankfully and it just worked. 2. To put things on a CD-R, everything uses .cdi image format. I couldn't find anything on macos that would burn them, and the tools on Linux just didn't make usable discs. Finally I just installed a 17 year old copy of DiskJuggler in WINE on Linux and that actually worked. Unfortunately it burns slowly if you don't have a license key (none of the keys worked, I guess I'll find a crack later.) I was able to get a copy of DiskJuggler off archive.org.