Is the CF drive on the 5D MKII and III using memory mode or IDE?
it is using IDE mode.
the camera first resets the card using IO pins, then via device control a soft reset.
then it issues an IDENTIFY DRIVE (0xEC) command.
according to the capabilities the firmware then it sends a SET FEATURES command (0xEF) to enable cache.
after an IDLE COMMAND (0xE3) with 500ms it enables UDMA mode using SET FEATURES (0xEF) again.
reading is done via commands READ SECTOR(S) (0x20) and READ DMA EXT (0x25) (PIO/DMA).
writing is done via commands WRITE SECTOR(S) (0x30) and WRITE DMA EXT (0x35) (PIO/DMA).
also the command FLUSH CACHE (0xE7) is being used for flushing buffers.
so there is nothing special being used by canon.
even a CD_ROM drive should work after we patch out the rotating drive check.