OPTEE RPMB Secure storage on high secure device

Good morning,

Please I am trying to use OPTEE RPMB secure storage on an High secure board. The only resource I found is this one : 

https://optee.readthedocs.io/en/latest/architecture/secure_storage.html which explains the theory about secure storage.

Please can you give me some code about how to manipulate OPTEE RPMB secure storage ?