OVMS3-idf/docs/api-reference/system/mem_alloc.rst

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Memory allocation
====================
Overview
--------
The ESP32 has multiple types of RAM. Internally, there's IRAM, DRAM as well as RAM that can be used as both. It's also
possible to connect external SPI flash to the ESP32; it's memory can be integrated into the ESP32s memory map using
the flash cache.
In order to make use of all this memory, esp-idf has a capabilities-based memory allocator. Basically, if you want to have
memory with certain properties (for example, DMA-capable, accessible by a certain PID, or capable of executing code), you
can create an OR-mask of the required capabilities and pass that to pvPortMallocCaps. For instance, the normal malloc
code internally allocates memory with ```pvPortMallocCaps(size, MALLOC_CAP_8BIT)``` in order to get data memory that is
byte-addressable.
Because malloc uses this allocation system as well, memory allocated using pvPortMallocCaps can be freed by calling
the standard ```free()``` function.
Internally, this allocator is split in two pieces. The allocator in the FreeRTOS directory can allocate memory from
tagged regions: a tag is an integer value and every region of free memory has one of these tags. The esp32-specific
code initializes these regions with specific tags, and contains the logic to select applicable tags from the
capabilities given by the user. While shown in the public API, tags are used in the communication between the two parts
and should not be used directly.
Special Uses
------------
If a certain memory structure is only addressed in 32-bit units, for example an array of ints or pointers, it can be
useful to allocate it with the MALLOC_CAP_32BIT flag. This also allows the allocator to give out IRAM memory; something
which it can't do for a normal malloc() call. This can help to use all the available memory in the ESP32.
API Reference
-------------
Header Files
^^^^^^^^^^^^
docs: use custom roles to generate GitHub links This change replaces direct links to GitHub master branch with auto-generated links using docutils custom roles. These auto-generated links point to the tree or blob for the git commit ID (or tag) of the repository. This is needed to ensure that links don’t become broken when files in master branch are moved around or deleted. The following roles are introduced: - :idf:`path` - points to directory inside ESP-IDF - :idf_blob:`path` - points to file inside ESP-IDF - :idf_raw:`path` - points to raw view of the file inside ESP-IDF - :component:`path` - points to directory inside ESP-IDF components dir - :component_blob:`path` - points to file inside ESP-IDF components dir - :component_raw:`path` - points to raw view of the file inside ESP-IDF components dir - :example:`path` - points to directory inside ESP-IDF examples dir - :example_blob:`path` - points to file inside ESP-IDF examples dir - :example_raw:`path` - points to raw view of the file inside ESP-IDF examples dir A check is added to the CI build script, which searches RST files for presence of hard-coded links (identified by tree/master, blob/master, or raw/master part of the URL). This check can be run manually: cd docs && make gh-linkcheck Additionally, Sphinx linkcheck build type is used to create new CI test, which check for broken links. This test has to be triggered explicitly, because including it in normal build process (when the commit is not yet deployed to Github) will not work. It can be triggered in a regular fashion using a combination of cron and Curl, similar to stress tests.
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* :component_file:`esp32/include/esp_heap_alloc_caps.h`
* :component_file:`freertos/include/freertos/heap_regions.h`
Macros
^^^^^^
.. doxygendefine:: MALLOC_CAP_EXEC
.. doxygendefine:: MALLOC_CAP_32BIT
.. doxygendefine:: MALLOC_CAP_8BIT
.. doxygendefine:: MALLOC_CAP_DMA
.. doxygendefine:: MALLOC_CAP_PID2
.. doxygendefine:: MALLOC_CAP_PID3
.. doxygendefine:: MALLOC_CAP_PID4
.. doxygendefine:: MALLOC_CAP_PID5
.. doxygendefine:: MALLOC_CAP_PID6
.. doxygendefine:: MALLOC_CAP_PID7
.. doxygendefine:: MALLOC_CAP_SPISRAM
.. doxygendefine:: MALLOC_CAP_INVALID
Type Definitions
^^^^^^^^^^^^^^^^
.. doxygentypedef:: HeapRegionTagged_t
Functions
^^^^^^^^^
.. doxygenfunction:: heap_alloc_caps_init
.. doxygenfunction:: pvPortMallocCaps
.. doxygenfunction:: xPortGetFreeHeapSizeCaps
.. doxygenfunction:: xPortGetMinimumEverFreeHeapSizeCaps
.. doxygenfunction:: vPortDefineHeapRegionsTagged
.. doxygenfunction:: pvPortMallocTagged
.. doxygenfunction:: vPortFreeTagged
.. doxygenfunction:: xPortGetMinimumEverFreeHeapSizeTagged
.. doxygenfunction:: xPortGetFreeHeapSizeTagged