MMIO register table

Register types:
 * R - Readable
 * W - Writeable
 * 8 - 8-bit access only
 * 16 - 8-bit access to either address, or 16-bit access to the lower address.
 * 24 - 8-bit or 16-bit access to 3 registers.
 * 8x2 - An internal 2-byte state accessed by two 8-bit read or writes (LSB first).