APIs Exported by Board-Specific Logic to NuttX

Exported board-specific interfaces are prototyped in the header file include/nuttx/board.h. There are many interfaces exported from board- to architecture-specific logic. But there are only a few exported from board-specific logic to common NuttX logic. Those few of those related to initialization will be discussed in this paragraph. There are others, like those used by `boardctl() <#boardctl>`__ that will be discussed in other paragraphs.

All of the board-specific interfaces used by the NuttX OS logic are for controlled board initialization. There are three points in time where you can insert custom, board-specific initialization logic:

First, <arch>_board_initialize(): This function is not called from the common OS logic, but rather from the architecture-specific power on reset logic. This is used only for initialization of very low-level things like configuration of GPIO pins, power settings, DRAM initialization, etc. The OS has not been initialized at this point, so you cannot allocate memory or initialize device drivers.

The other two board initialization hooks are called from the OS start-up logic and are described in the following paragraphs: