d53e9519a1
the time() implementation now uses sys_clock_gettime(), change that in the docs. Signed-off-by: Fin Maaß <f.maass@vogl-electronic.com>
48 lines
2.1 KiB
ReStructuredText
48 lines
2.1 KiB
ReStructuredText
.. _c_library_common:
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Common C library code
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#####################
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Zephyr provides some C library functions that are designed to be used in
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conjunction with multiple C libraries. These either provide functions not
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available in multiple C libraries or are designed to replace functionality
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in the C library with code better suited for use in the Zephyr environment
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Time function
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*************
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This provides an implementation of the standard C function, :c:func:`time`,
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relying on the Zephyr function, :c:func:`sys_clock_gettime`. This function can
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be enabled by selecting :kconfig:option:`COMMON_LIBC_TIME`.
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Dynamic Memory Management
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*************************
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The common dynamic memory management implementation can be enabled by
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selecting the :kconfig:option:`CONFIG_COMMON_LIBC_MALLOC` in the
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application configuration file.
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The common C library internally uses the :ref:`kernel memory heap API
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<heap_v2>` to manage the memory heap used by the standard dynamic memory
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management interface functions such as :c:func:`malloc` and :c:func:`free`.
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The internal memory heap is normally located in the ``.bss`` section. When
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userspace is enabled, however, it is placed in a dedicated memory partition
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called ``z_malloc_partition``, which can be accessed from the user mode
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threads. The size of the internal memory heap is specified by the
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:kconfig:option:`CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE`.
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The default heap size for applications using the common C library is zero
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(no heap). For other C library users, if there is an MMU present, then the
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default heap is 16kB. Otherwise, the heap uses all available memory.
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There are also separate controls to select :c:func:`calloc`
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(:kconfig:option:`COMMON_LIBC_CALLOC`) and :c:func:`reallocarray`
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(:kconfig:option:`COMMON_LIBC_REALLOCARRAY`). Both of these are enabled by
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default as that doesn't impact memory usage in applications not using them.
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The standard dynamic memory management interface functions implemented by
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the common C library are thread safe and may be simultaneously called by
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multiple threads. These functions are implemented in
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:file:`lib/libc/common/source/stdlib/malloc.c`.
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