That's a higher level function than I'm tackling - I'm just implementing a block transfer device driver; and anyone who includes NABUduino.h in their project can access it.
If somebody built a boot ROM that included the relevant routines from NABUduino.c; the machine could boot from a SD card with the proper boot files on it; or if a version of CP/M was built with support for reading image files from the NABUduino's SD card slot, it could be treated as a hard drive.
After I built the NABUduino PCB files; I also built a board that inserts an ESP32 in between the HCCA UART chip and the RS422 line drivers. I included one of those in the boxes I sent you and DJ Sures. That PCB has ports on it for a PS/2 mouse, SD card, and software generated VGA (via the FABGL library) as well; and I'm expecting that's the one that DJ Sures is going to put support for into Cloud CP/M.
The repository for the ESP32 card is here:
GitHub - bdurbrow/NABU-ESP32-TR1863
Contribute to bdurbrow/NABU-ESP32-TR1863 development by creating an account on GitHub.
github.com
At the moment however; the only firmware that's up in that repository is a very simple echo routine that makes it more-or-less transparent so that the NABU can boot from a PC connected via a RS422-USB adapter and DJ Sures' NABU Internet Adapter software while the ESP32 card is plugged into the NABU's motherboard.