As of yesterday, DEVROM itself can detect a memory card during reset. When detected it will continue to boot from there instead of jumping to the built-in main menu. This means you don't need the Arduino route anymore when playing with the expander.

Naturally everything still needs refinements. But from here we can theoretically bootstrap an entire new system without ever updating the EPROM again, and without being tethered to a laptop/PC.

Some unrelated but noteworthy recent updates:

• Preliminary interrupt support is now available (vIRQ)
• We have the ROM files discoverable with a new function: SYS_ReadRomDir. With this we can iterate over the built-in files and get their ROM address for reading. I can see this become useful in a simple command line shell. Or for making libraries.
• TinyBASIC now accepts hexadecimal numbers ($....) in expressions. This could be squeezed in without sacrificing free bytes.