Hello everyone, it's time for another update!
I have fixed the majority of bus timing issues with the Z80 and the AVR. There are still a couple little bugs that caused failed boots, but i have managed to get text on the screen! I am also going to be redoing the case as the one i made broke.
What's next for this project is to make a simple ROM monitor to load programs into RAM, and to write a few programs for it for testing! I also will need to write AVR code for processing sound and reading from / writing to the cartridges. Once I am sure everything works as it should I will publish all the designs and code for everyone to use.