How good is SecRandomCopyBytes?

I'm principally interested in the implementation of SecRandomCopyBytes on iOS, if it differs from the OS X implementation. (I would presume that it does, since a mobile device has more and more readily available sources of entropy than a desktop computer.)

Does anyone have information on:

1. Where SecRandomCopyBytes gets entropy from?
2. What rate it can generate good random numbers?
3. Will it block, or fail immediately if not enough entropy is available?
4. Is it FIPS 140-2 compliant, or has it been included in any other official certification?

The documentation does not cover these points.

I've only been able to find hear-say comments that it uses information from radios, the compass, accelerometers and other sources, but no quotes from people actually representing Apple.