102 lines
5.1 KiB
ReStructuredText
102 lines
5.1 KiB
ReStructuredText
==================================
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Naming and Header File Conventions
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==================================
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- **Common Microprocessor Interfaces**. Any interface that is
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common to all microprocessors should be prefixed with ``up_``
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and prototyped in ``include/nuttx/arch.h``. The definitions in
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that header file provide the common interface between NuttX and
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the architecture-specific implementation in ``arch/``.
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``up_`` is supposed to stand for microprocessor; the ``u``
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is like the Greek letter micron: ľ. So it would be ``ľP``
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which is a common shortening of the word microprocessor. I
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don't like that name very much. I wish I would have used a
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more obvious prefix like ``arch_`` instead -- then I would
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not have to answer this question so often.
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- **Microprocessor-Specific Interfaces**. An interface which is
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unique to a certain microprocessor should be prefixed with the
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name of the microprocessor, for example ``stm32_``, and be
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prototyped in some header file in the ``arch/`` directories.
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There is also a ``arch/<architecture>/include/<chip>/chip.h``
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header file that can be used to communicate other
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microprocessor-specific information between the board logic and
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even application logic. Application logic may, for example,
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need to know specific capabilities of the chip. Prototypes in
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that ``chip.h`` header file should follow the
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microprocessor-specific naming convention.
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- **Common Board Interfaces**. Any interface that is common to
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all boards should be prefixed with ``board_`` and should also
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be prototyped in ``include/nuttx/board.h``. These ``board_``
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definitions provide the interface between the board-level logic
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and the commaon and architecture-specific logic.
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- **Board-Specific Interfaces**. Any interface which is unique to
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a board should be prefixed with the board name, for example
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``stm32f4discovery_``. Sometimes the board name is too long so
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``stm32_`` would be okay too. These should be prototyped in
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``boards/<arch>/<chip>/<board>/src/<board>.h`` and should not
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be used outside of that directory since board-specific
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definitions have no meaning outside of the board directory.
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- **Scope of Inclusions**. Header files are made accessible to
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internal OS logic and to applications through symbolic links
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and through *include paths* that are provided to the C/C++
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compiler. Through these include paths, the NuttX build system
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also enforces modularity in the design. For example, one
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important design principle is architectural *layering*. In this
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case I am referring to the OS as layered into application
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interface, common internal OS logic, and lower level
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platform-specific layers. The platform-specific layers all
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reside in the either ``arch/`` sub-directories on the
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``config/`` subdirectories: The former sub-directories are
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reserved for microcontroller-specific logic and the latter for
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board-specific logic.
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In the strict, layered NuttX architecture, the upper level OS
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services are always available to platform-specific logic.
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However, the opposite is *not* true: Common OS logic must never
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have any dependency on the lower level platform-specific code.
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The OS logic must be totally agnostic about its hardware
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environment. Similarly, microcontroller-specific logic was be
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completely ignorant of board-specific logic.
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This strict layering is enforced in the NuttX build system by
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controlling the compiler include paths: Higher level code can
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never include header files from either; of the
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platform-specific source directories; microcontroller-specific
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code can never include header files from the board-specific
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source directories. The board-specific directories are, then,
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at the bottom of the layered hierarchy.
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An exception to these inclusion restrictions is the
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platform-specific *include/*. These are made available to
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higher level OS logic. The microcontroller-specific include
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directory will be linked at ``include/arch/chip`` and, hence,
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can be included like ``#include <arch/hardware/chip.h``.
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Similarly, the board-specific include directory will be linked
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at ``include/arch/board`` and, hence, can be included like
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``#include <arch/board/board.h``.
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Keeping in the spirit of the layered architecture, these
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publicly visible header files must *not* export
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platform-specific definitions; Only platform-specific
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realizations of standardized declarations should be visible.
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Those *standardized declarations* should appear in common
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header files such as those provided by ``include/nuttx/arch.h``
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and ``include/nuttx/board.h``. Similarly, these publicly
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visible header file must *not* include files that reside in the
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inaccessible platform-specific source directories. For example,
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the board-specific
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``boards/<arch>/<chip>/<board>/include/board.h`` header file
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must never include microcontroller-specific header files that
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reside in ``arch/<arch>/src/<mcu>``. That practice will cause
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inclusion failures when the publicly visible file is included
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in common logic outside of the platform-specific source
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directories.
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