this is cool as heck! i love the amount of documentation and software you’ve provided. i’ll definitely have to look into this further.
it’s very similar to a fantasy console that i made several years ago called “diode”. it had an 8x8 instead of a 16x16 screen so that i could use off-the-shelf 8x8 LED matrices for it, but it was similar in other ways - it also had 256 bytes of RAM and a controller with a d-pad and 2 action buttons. however, it was a harvard architecture machine where the RAM and ROM (also 256 bytes) were in two separate address spaces.
i even created a real handheld console for it that ran on an arduino nano with interchangeable game cartridges that contained I2C EEPROM chips, but sadly that project seems to have been lost to time. annoyingly, i can’t even find any photos of it. maybe someday i’ll also try to make a real, physical console for tny as well!