Porting CP/M-65 to the KIM-1

Update: David Given has already merged my KIM-1 ports into his repository, so they are now part of the main branch.

It seems that everything related to CODOS 1.0, MTU’s operating system that was meant to work along with the K-1013, is lost. Only images of CODOS 2.0 for the MTU-130 and MTU-140 exist and, although that computer also uses a K-1013, it has a more complex arqchitecture so that version is not compatible with the KIM.

So, that posed a question for my K-1013 replica project: which software am i running with it?

Then, I stumbled upon Davis Given’s CP/M-65, a modern rewrite of the popular operating system that targets the 6502 CPU. It supported some popular machines, like the BBC Micro, the Apple ][ or even the PET, and was very well written and structured, so it seemed a very good candidate.

The K-1013 emulation in my Pico based RAM/ROM/Video/FDC card was also reasonably complete, so I just got down to work. The most difficult part was to understand the complex, Python based, build system. Once I did, just created a new folder for the architecture dependent parts of the port, which are just the loader and the BIOS, had a good look at the other ports and started coding. A couple of days later, I got it running:

This will make and excellent testbed for the real K-1013 when it is finished and will give it some utility, too. But not many people was going to benefit from that. Then, I saw Ryan Roth’s implementation of a very simple SD card interface with the KIM. Adapting that to the existing port was a matter of a few hours, so that brought the OS to users of even less poerful systems, like the PAL-1:

The requirements are very simple:

• RAM expansion that fills the memory hole from 0x0400 to 0x13FF and provides at least 32K from 0x2000, but full expansion up to 0xFF00 is advisable.
• An SDHC card of any capacity (only 32MB are used) and a generic Arduino SD card adapter with 5V to 3.3V conversion. See Ryan’s repository for detailed requisites and connection instructions.

And finally, David had already made a 1541 based port for the C-64 and I had the IEC routines for the KIM from the xkim1541 project, so it was just trivial to add that too. If you don’t mind seeing your beard grow while it works, you can also run CP/M-65 on a KIM-1 or PAL-1 equiped with an IEC disk:

It has a few limitations, though:

• It only currently works for 1541 drives (or pi1541 with 1541 personality). Other drives or SDIEC are not supported.
• Did I say that it is slow as hell?