Hi there, after some struggle I've managed to get even closer to the end. What I got now is an almost working version. Yes, this time I have burnt an EPROM (the last empty one I had - I don't have an eraser, but I've already ordered some EEPROMS) and tested in on real hardware.

• the new parameter 1-4 is unlocked and you can change its value from 1 to 8
• LEDs connected to upd7810 show the correct binary value (i.e. port and latch are working fine)
• you can save and recall the bank number to/from SRAM

Looks nice, huh? So what's wrong?

• sometimes even if the value is set properly (cycling from 1 to 8), it doesn't get send to the hardware (now I need to figure out if it's because of wrong value being read or set)
• after restart, saved bank values are messed up

I have an idea why the first problem occurs, it's probably because the bank switching handler is not interrupt safe. Even if the fix looks easy to implement, I have another problem - keep reading.

As for the second part, I think I could modify my emulator so that the SRAM is not handled as an ordinary RAM but rather saved and loaded to a file. That would give me an opportunity to see how it behaves after reboot.

Now, my biggest problem is the available memory, or lack of it. I managed to squeeze my code into the EPROM, but I had to sacrifice a few lines of code to do that. Some time ago I said, that my plan B would be to remove tape saving and loading routines, because that's someting nobody's gonna use, especially if there's MIDI available. So far I have removed the code that clears the value on displays before writing TAPE on them. Not a big deal, now it looks more like TAPE_1 or TAPE<whatever walue was set>. I think, I will remove saving to tape first, because even if there's a slightliest chance, that somebody has some old patches stored on tape or wave file, I really doubt that anybody would like to save anything back to tape...

I may have another session with debugger this weekend. I'll keep you informed.