MPU_BANK_SWITCHING

Emulates any C64 memory bank-switching that could be considered as being
useful for emulation of C64 music players. This should be the preferred
setting.


MPU_TRANSPARENT_ROM

A simplified emulator environment with partial C64 memory bank-switching.
Not as powerful as MPU_BANK_SWITCHING, but allows running sidtunes which

 - use the RAM under the I/O address space
 - use RAM at $E000-$FFFA + jump to Kernal functions

If a sidtune requires this mode to be enabled, the sidtune ought to be
fixed to make proper use of bank-switching.


MPU_PLAYSID_ENVIRONMENT

A PlaySID-like emulator environment. Allows running sidtunes which:

 - are specific to PlaySID
 - do not contain bank-switching code
 - would not run on a real C64 because their players were prepared
   to assume the certain emulator environment provided by PlaySID

If a sidtune requires this mode to be enabled, the sidtune ought to be
fixed to make proper use of bank-switching.