MP Initiaton - with and without extension hooked up

Last time I did a post on calibration data. This time I'll talk about the general initiation scheme of the MotionPlus(MP) Extension. There are two possible cases which are handled in my scheme below - either there's an extension connected or none connected to the motion plus pass-through port. Parts that are marked blue are specific for the MP, yellows parts are done additionally when an extension was connected to the MP.

Games will usually start with requesting a status report. When the MP already  has been active, it will be deactivated by the following Init() (write 0x55 to 0xA400F0  and 0x00 to 0xA400FB) and a corresponding status report 0x20 will be scheduled. Afterwards the game will usually try to read out the extensions ID  within the active extension register located at 0x(A400)FA. If there was an extension hooked up to the Wiimote besides the MP, we'll find  its corresponding ID at that place and the game starts encryption( the so called "old way", but it's the way games do it). It's done by writing a 16bytes long key splitted in three chunks (6bytes,6bytes,4bytes) at 0x(A400)40. Extension data wil be encrypted from now on (calibration data, active extension register data). When the encryption was set, the game will read out the calibration data encrypted from the extension device connected to the MP.

As soon that is done, the game will check if there's a MP available by attempting to read from A600FE. It will return the corresponding MP extension ID. If the MP has already been activated earlier and has not been deactivated somehow - which shouldn't be the case, since the game was clever enough to do an Init() at the beginning of the whole handshake, which disables the MP and activates the regular extension- it will throw out a readerror. The readerror would mean at this place, there was no MP present at all. You could check that, by simply comparing the active extension ID or resp. do another Init() and do the whole cycle other again. If the extension ID was found at register 0xA600FE, the game will issue a MP Init(2) .The Init2() consists of a 0x55 single byte write to 0xA600F0 and a 0x05 single byte write to 0xA600FE. The byte written to 0xA600FE varies, depending on what extension the game still might want to use or what it already has found. When only the MP is needed, it would just write 0x04 to 0xA600FE instead, if it does need the nunchuk for instance as well, it would write 0x05 to passthrough the extension data from the nunchuk.
Apart from that, you could also just write 0x05 even if u only have a MP. The written single byte to 0xA600FE, will initiate a registerswap(0xA4xxxx and 0xA6xxxx) and a status report about a new connected extension will be sent out by all means. If there was a passthrough extension connected, there will be first a  status report send out, informing you of a disconnection of the current active extension, and then the regular one noticing you of a connection, will be sent out. Now, since the extension registers got swapped, readerrors will occur on readattempts to the former MP extension ID at 0xA600FE. The game will expect those read errors since it just activated the MP. It will read as long there was no status report (extension connected) issued, which usually takes a period of 2-3 read attempts. When no report gets issued, the game will just issue another Init() to play the whole cycle over again after some time. When the report got issued, the game will write a 0x00 single byte to 0xA400FB, to ready up the device and refresh the data reporting, due an "unrequested (connection) status reports.

The game will try to verify a last time whether it's the right extension(MP), and will read out its extension ID at 0xA400FA. Which should read 00 00 A4(instead of A6, gets changed because of the page mapping) 20 05(depending on what you wrote to 0xA600FE earlier) 05. When this all is settled, the game will request calibration data from the active extension register at 0x20-0x3f just like for regular extensions . If there was an extension hooked up to the MP extension port, calibration data will be requested, which resides noncrypted at 0xA40040. Motionplus supporting games will usually validate the extensions calibration data checksum (last 2 bytes of it). If it's incorrect it will issue a 0x01 write to 0xA400F3h. The game will explicitly disable the MP and try to do the whole Init() over again. If the validation was passed, the game will now request syncdata at 0x50-0x8f, to sync up MP data with Wiimote accel data which is needed to get "6DOF". This is needed to correlate regular accel velocities and angular accel for absolute orientation.

I hope this was some clear and any helpful. Be fair and don't forgot to link if your passing stuff.

In my next posting I will hopefully be able to present you chaps a way more complete and corrected calibration data scheme and maybe already a small scheme on issued sync-data since I already know how to make the MP generate new sync data! So knowing how the syncdata is splitted, would be very helpful for a lot of people, since we won't need to do the calibration ourselves anymore - like most fellas are doing it at the moment, esp. those who are working on robotic stuff.;)

Best regards
Sanchez