Hi all.
I spent some time on reversing the mc9620. I have almost found the jtag interface (I say almost because it is not reliable, and I cannot use it to stop and debug the processor) Nevertheless, I managed to dump the firmware of the tetrapol 55522d chipset, an Atmel arm7tdmi that share some design with old at91 chips
I found some stuff (message queue, state machine, gui).
But what is important and that I would like to share with you is that I found some info on how it interfaces to the Texas C54 dsp, and that I was able to extract the dsp firmware, where surely all the undocumented things happen (voice and encryption).
I am know focusing on reversing the dsp firmware (not an easy task). If anybody is interested in helping, don't hesitate !
Best