* CALL nn takes 6 cycles on the GBZ80, but 5 NOPs on the Z80
* ADD HL,ss takes 2 cycles on the GBZ80, but 3 NOPs on the Z80
* JP cc,nn has different timings depending on whether the jump is taken. This is not the case on Z80.
Flags can differ too:
*[https://gbdev.gg8.se/wiki/ GBDev wiki]
*[https://emudev.de/ Emudev (q00.gb)]
*[https://gekkio.fi/files/gb-docs/gbctr.pdf Game Boy Complete Technical Reference]
*[https://github.com/SingleStepTests Tom Harte's SingleStepTests]