Direct USB to gcnclient connection

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This is a documention on the protocol from direct USB to the gcnclient on the computer as it is a bit different than the normal gCn client (documented by Sorunome).

I have only tried b-messages, I guess f-messages would be pretty similar, I have also only tried it over the DCSB basic libraries, and it seems to me that basic libraries add 3 bytes for some reason.

Usually a gCn message has a header, and in the case of b or f messages 2 bytes \xFF and \x89 right after the header for arduino handling. Those 5 bytes are omitted when sending. In addition is the last byte, the \x2A or '*' also been omitted. Now the message looks like this:

<5 bytes recipient id><5 bytes sending id><message payload 2 byte little endian><message>

For example we send a b-message from the id ffffffffff containing 'Hello World'

\x00\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\x0B\x00Hello World

Now, if you'll try to use it with the BASIC libs (i think it is only the basic libs) you'll find that it won't work, because of the weird encoding i found: the message needs to be enhanced by three bytes: the byte \x04 and again it's length encoded as little endian. so now sending Hello World would look like this:

\x00\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\x0E\x00\x04\x0B\x00Hello World

Python Example

After setting up an active connection to the calculator using libusb this function will create a string that needs to be sent to the calculator (using a b-message). Note that this creates the string, it doesn't send it.

def getMessage(message):
        message = struct.pack("<H",len(message))+message #we add the DCSB payload
        message = "\x04"+message #we add the misterious DCSB byte
        message="\x00\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF"+struct.pack("<H",len(message))+message #we set the recipiant id to 00 because it is a b-message and the sender id to ff because it isn't a real calc, then we add the new payload and the message
        print "Created Message "+":".join("{0:x}".format(ord(c)) for c in message) #debug output as hexadecimal
        return message

Basic example

This program sends 'PING' to the server and then wait for a reply, storing it in Str9. It won't exit until [clear] is been hit, if there is a reply it'll output at least once 1. After exiting the program with [clear] Str9 is the content of the latest recieved message of the server.

:9999999999→ϴ
:0→C
:"→Str9
:sum(19,1 //set up gCn
:sum(17,"PING //send to server
:Repeat C=45 //wait until clear is been pressed
:getKey→C
:sum(20,1 //check if we need to recieve something
:Disp Ans //debug
:If Ans //if we need to recieve something
:sum(18 //we recieve, data is been stored in Str9
:End
:sum(19,0 //close gCn