GameBoy’s CPU is different from z80 or 8080. This is a custom CPU. But it is very similar to 8080.
My program is 8080 emulation, not work GameBoy 's ROM.
SPI RAM is definitely not fast, but it’s late and not problematic.
(It is not suitable for action games etc. However it is a fact that there is no other method.Still it may be operating faster than the actual 8080 machine)
By the way, you can read and write one byte at a time.
Currently my 8080 emulator has passed the famous CPU check program. However, Altair BASIC is not working properly.
The destination seems to be still far.