in the Merriefield SOC there are:
1. Punit
2. SCU
3. Dual core Silvermont.
The Puinit is internal and a big mystery ever around here.
The SCU is and interface that starts the system and controls some the the internal interfaces and starts the BIOS or equivalent.
The Silvermont is the real processor. It may make I/O requests to the SCU (we use IPC calls, I believe there is a mialbox in ram). The SCU may ore may not process the request depending on sercurity policies or other things.
John Kabat (Intel)