The default setup on startup is 4 cycles for ROM access as you mention, but with system control registers you can control how fast the memory is - apparently cu

The default setup on startup is 4 cycles for ROM access as you mention, but with system control registers you can control how fast the memory is - apparently current ROM has 3/1 wait states (first/sequential) access for 16 Bit access. There’s also a prefetch queue instructions. I understand this means when running THUMB code from ROM, non-branching instructions can also run at full speed. https://problemkaputt.de/gbatek.htm#gbasystemcontrol https://problemkaputt.de/gbatek.htm#gbasystemcontrol