This is worth another project log...
Since I got "boot from RAM" working yesterday, I eagerly started implementing the basic BIOS/BDOS functions of CP/M 2.2. No disk access, yet, but just the standard console input/output and housekeeping functions.
Fortunately, CP/M is well documented and there aren't actually that many functions that need to be implemented for a basic system.
So, I fixed my broken LCD DDRAM mapping and optimized the keyboard handler a little and added the most important CP/M BDOS functions.
Then I took a small .COM file (SYSGEN), placed it into RAM and jumped to it...
I was greeted by the program banner! It works!
That was really unexpectedly simple! The next 1-2 weeks will be used to implement a simple file system and all the necessary open/close/read/write functions, so we all can play ZORK before the year is over! :-)