1. how does rockbox handle deadlocks?
Using cooperative multi-tasking, deadlocks are actually hard to achive! ;-) We don't do anything particular to handle them.
2. what is its process scheduling and process synchroniztion
We do cooperative multi-tasking, we don't have "process synchroniztion" really. Although we have mutexes and message queus for working in and outside of interrupts.
3. its memory management
We basically only have static fixed buffers, no dynamic memory allocation at all. The exception is that some parts of the system can "nick" parts of the audio buffer at startup as a form of "dynamic" memory.
4. input and output systems
What's the question? We have button, joystick, scrollweel, etc input and we have LCD output.
5. security and protection
Protection of what? Security on what sense?