Where to start with ARM Trust-zone development for Cortex-A series?


I am a new Graduate student and am looking at building trusted applications for mobile and embedded devices using the Cortex-A series of processors.

I am an absolute beginner in this department and really need some help getting started, but here is some of the stuff I have found.  

I found a lot of information about using the Cortex-M series.   I could possibly use a Cortex-M, but would prefer to use the A series.

Is there a guide for the Cortex-A that I could use to get started?

Would I be able use a Raspberry Pi to implement a trust-zone and secure applications?  I find different responses on the RPI's ability to secure a Trustzone. 

If not which development boards would be good to start learning on?

Any help with getting started would a huge help.

Thanks everyone.

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