Wow, thats news to me. Its been there since the A7 apparently and is used to process the fingerprint sensor data:
"The Secure Enclave uses encrypted memory and includes a hardware random number
generator. Its microkernel is based on the L4 family, with modifications by Apple.
Communication between the Secure Enclave and the application processor is isolated
to an interrupt-driven mailbox and shared memory data buffers.
Each Secure Enclave is provisioned during fabrication with its own UID (Unique ID) that is
not accessible to other parts of the system and is not known to Apple. When the device
starts up, an ephemeral key is created, entangled with its UID, and used to encrypt the
Secure Enclave’s portion of the device’s memory space."
A big part of what Chipworks does (as a company) is reverse engineering silicon from die shots and x-rays and such. They're not just going to hand this kind of information out on a platter - they were commissioned to do a cursory glance for this puff piece.
But it also doesn't take a genius to guess at what the various hardware modules do just given what the iPhone can do.
[1] http://images.apple.com/privacy/docs/iOS_Security_Guide_Sept...