mraa/docs/platform-hooks.md

Hooks can be defined per supported platform to allow for highly custom operations if needed.
This feature of MRAA should only be used by developers defining the board definitions, NOT an end user.

##Types of Hooks

###REPLACE
Defining a replace function will entirely replace the associate function. This should only be done if your new function can handle everything the mraa function would normally.

###PRE
Any functionality defined here will be performed when the main function is called.

###POST
Any functionality perfomed here is done just before the normal function returns. All post functions will have passed into them the return value that would normally be returned.

##Hooks
### GPIO
 * init (pre-post)
 * mode (replace-pre-post)
 * dir (replace-pre-post)
 * write (pre-post)
 * use-mmaped (replace-pre-post)

### I2C
 * init (pre-post) - On RAW