Hardware/DMCU

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

Firmware

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.