75 lines
3.4 KiB
ReStructuredText
75 lines
3.4 KiB
ReStructuredText
==============================================
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APIs Exported by Board-Specific Logic to NuttX
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==============================================
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Exported board-specific interfaces are prototyped in the header
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file ``include/nuttx/board.h``. There are many interfaces exported
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from board- to architecture-specific logic. But there are only a
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few exported from board-specific logic to common NuttX logic.
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Those few of those related to initialization will be discussed in
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this paragraph. There are others, like those used by
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```boardctl()`` <#boardctl>`__ that will be discussed in other
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paragraphs.
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All of the board-specific interfaces used by the NuttX OS logic
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are for controlled board initialization. There are three points in
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time where you can insert custom, board-specific initialization
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logic:
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First, ``<arch>_board_initialize()``: This function is *not*
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called from the common OS logic, but rather from the
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architecture-specific power on reset logic. This is used only for
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initialization of very low-level things like configuration of GPIO
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pins, power settings, DRAM initialization, etc. The OS has not
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been initialized at this point, so you cannot allocate memory or
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initialize device drivers.
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The other two board initialization *hooks* are called from the OS
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start-up logic and are described in the following paragraphs:
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.. c:function:: void board_early_initialize(void)
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The next level of initialization is performed by a call to
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``up_initialize()`` (in
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``arch/<arch>/src/common/up_initialize.c``). The OS has been
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initialized at this point and it is okay to initialize drivers in
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this phase. ``up_initialize()`` is *not* a board-specific
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interface, but rather an architecture-specific, board-independent
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interface.
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But at this same point in time, the OS will also call a
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board-specific initialization function named
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``board_early_initialize()`` if
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``CONFIG_BOARD_EARLY_INITIALIZE=y`` is selected in the
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configuration. The context in which ``board_early_initialize()``
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executes is suitable for early initialization of most, simple
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device drivers and is a logical, board-specific extension of
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up_initialize().
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``board_early_initialize()`` runs on the startup, initialization
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thread. Some initialization operations cannot be performed on the
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start-up, initialization thread. That is because the
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initialization thread cannot wait for event. Waiting may be
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required, for example, to mount a file system or or initialize a
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device such as an SD card. For this reason, such driver initialize
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must be deferred to ``board_late_initialize()``.
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.. c:function:: void board_late_initialize(void)
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And, finally, just before the user application code starts. If
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``CONFIG_BOARD_LATE_INITIALIZE=y`` is selected in the
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configuration, then an final, additional initialization call will
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be performed in the boot-up sequence to a function called
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``board_late_initialize()``. ``board_late_initialize()`` will be
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called well after ``up_initialize()`` and
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``board_early_initialize()`` are called.
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``board_late_initialize()`` will be called just before the main
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application task is started. This additional initialization phase
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may be used, for example, to initialize more complex,
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board-specific device drivers.
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Waiting for events, use of I2C, SPI, etc are permissible in the
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context of board_late_initialize(). That is because
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``board_late_initialize()`` will run on a temporary, internal
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kernel thread.
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