*[[8255|PPI]] has more functionalities than what the CPC needs.
*[[PSG]] cannot be accessed directly as it is behind the PPI. It is simple to emulate though, but it cannot do much.
*[[FDC|765 FDC]] is bloated, with 40 pins , compared to 28 pins for the WD1772 FDC used in the [[Atari ST]]. It is also a black box internally, while the [[C64]] uses a regular 6502 (with its own ROM and RAM) as FDC.
Thankfully, many tools and tests exist to help emulation authors.