Compact Flash adapters on the GBA cartridge interface all generally work by exposing IDE registers using the top eight address bits coupled with the sixteen-bit data bus, wiring them directly to the relevant IDE connector pins.

In programmer-facing documentation, the two address ranges mentioned (matching PC I/O) are 1F0h-1F7h and 3F0-3F7h. In hardware, the choice is controled by Chip Select (CS) pins, while the specific register is chosen using DA0-DA2.

TODO:

• Is INTRQ relayed in any way? On which adapters?

Identification:

• 0B4h (device type) == 24h
• 0BFh - bit 7 clear
• 1FFFFh - bit 7 clear

Timings:

• Official software uses default timings (EXMEMCNT[6:0] = 00h).

Memory map:

• 240000h - unlock register (32-bit)
  • bit 0 - set if unlocked, clear if locked
  • bit 1-31 - unknown
• 1000000h - 8 megabytes of memory starts here

TODO:

• what are the remaining unlock register bits?
  • official software crashes if any bits 16-31 are set on initialization
• does the unlock register control memory visibility or just writability?