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The DMCU is a M68HC11 compatible microcontroller which manages the Display Controller while in vWii mode.


The DMCU firmware is loaded by nn_cmpt.rpl. The firmware is stored in OSv0/OSv1 in ASCII text form with a NULL terminator at the end.

Each line starts with the address in hex, prefixed with an @, followed by one or more bytes in hex written to the address, and ends with a LF character.

The following line would write AB CD to address 0123:

@0123 AB CD

Memory Map

Address range Size Description
0x0000-0x00ff 0x100 RAM (Contains soft registers)
0x0100-0x5fff 0x5F00 External RAM (Contains data, text, rodata, and stack)
0x8000-0x803F 0x40 M68HC11 control registers
0x8100-0x93FF[check] 0x1300 DC write registers 0x4100+
0x9400-0x940F 0x10 DC interface registers
0x9600-0xBFFF[check] 0x2A00 DC write registers 0x5600+
0xFFC0-0xFFFF 0x40 Vectors

DC Interface

DC Interface Registers
Address Bits Name Description
0x9402 8 Write Control DMCU waits for the lowest bit to be set before performing any writes
0x9404 32 Write Data Little endian value which can be used to perform a 32-bit write
0x9408 16 Read Address Address divided by 4 to read from the DC
0x940A 8 Read Control DMCU waits for the lowest bit to be set after writing to Read Address
0x940C 32 Read Data Little endian value which contains the data from a 32-bit read

To write to the DC, wait for the lowest Write Control bit to be set, then write a 8 bit value to any of the DC write registers. Writing 0xFF to a register triggers a 32-bit write using the Write Data register.

To read from the DC, write an address to Read Address and wait for the lowest Read Control bit to be set. Read Data now contains the data read.