Gamecube USB/ATA interface:

1,2,3

ATA/IDE tech ref
GC DD interface tech ref

Principle of operation:

FPGA communicates with GC DD interface and records 12 byte command sent by GC.
If the fpga is set to USB only mode then the fpga will send the commands to the PC server and the PC will respond with the correct data with the fpga acting as the arbiter.

If the fpga is set to ATA mode then it will convert the commands to an appropriate HDD or atapi ODD command and fetch the data from the drive and send to the GC.

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Links of interest:
tmb
kev
bun
afro

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