Rockbox, iTrip and iPod
There are two main thing that are needed by the iTrip to work:
1: The first thing is the power supply on the dock connector
2: The second thing is the apple protocol which allows sending commands trough the dock connector to the iTrip.
To fix the first thing I went to the Rockbox's IRC channel, and to tell you the truth I was amassed about the help I got there, the rockbox team is really co-operative, I must thank especially to linuxstb, he helped me a lot with directing me to the right places, so after testing some of the codes from the iPodLinux project, we found out which one turns the power supply on, and now its already in the cvs tree.
So the first thing seems to be done, now we have power supply on the dock connector, so some of the iPod accessories may already work.
The second thing is a bit tricky, for the moment we don't really have a working apple protocol on 4 and 5g iPods, so there is no way to send commands to the iTrip which are required to turn the iTrip on because even if you have power on you dock connector, the iTrip won't power up till it receives the play command.
But don't worry, there is a solution for this :) it's not the best one, but it works. So what I did was to get the iTrip apart and found out which pins are used for the power supply. See here for the dock connector numbering.
The ones used for power are:
Pin 1 - Ground
Pin 17 + 3V
So if you take two little wires and meld them to this pins on the iTrip then you will be able to attach a second power supply to it which don't needs to be always on, just for a few seconds.
So if you done this, dock the iTrip to your iPod, fire up the original firmware and press play, this will turn the iTrip on, now connect you second power supply to the iTrip and restart your iPod by holding the Select+Menu buttons pressed. You will notice that even when your iPod is of the iTrip is still on, so you can now boot into Rockbox and disconnect the second power supply because we have power with Rockbox too.
So that's it, now you just select your preferred music and listen them on the radio :)
I attached two little flat batteries to the back of the iTrip with a little button, so I just press that small button when I reboot into Rockbox and everything works fine.
Enjoy, I hope it will be helpful to you or someone :)