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change(heap): reserve DMA pool with low priority MALLOC_CAP_DEFAULT caps

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wuzhenghui
2026-07-09 17:39:04 +08:00
parent 3abe86a894
commit 9dc97e2faf
6 changed files with 26 additions and 31 deletions
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docs/en/api-guides/external-ram.rst
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@@ -97,7 +97,14 @@ An additional configuration item, :ref:`CONFIG_SPIRAM_MALLOC_ALWAYSINTERNAL`, ca
If a suitable block of preferred internal/external memory is not available, the allocator will try the other type of memory.
Because some buffers can only be allocated in internal memory, a second configuration item :ref:`CONFIG_SPIRAM_MALLOC_RESERVE_INTERNAL` defines a pool of internal memory which is reserved for *only* explicitly internal allocations (such as memory for DMA use). Regular ``malloc()`` will not allocate from this pool. The :ref:`MALLOC_CAP_DMA <dma-capable-memory>` and ``MALLOC_CAP_INTERNAL`` flags can be used to allocate memory from this pool.
Because some buffers can only be allocated in internal memory, a second configuration item :ref:`CONFIG_SPIRAM_MALLOC_RESERVE_INTERNAL` reserves a pool of internal DMA-capable memory at startup (in ``main_task``, after PSRAM is initialized). The pool is malloc from the regular internal heaps and re-registered as separate heap pool.
The reserved pool uses the heap capability priority mechanism:
- **Medium priority** — ``MALLOC_CAP_DMA | MALLOC_CAP_INTERNAL``: explicit ``heap_caps_malloc()`` requests with these flags are preferentially served from this pool.
- **Low priority** — ``MALLOC_CAP_DEFAULT``: ``malloc()`` may use the pool only after other internal heaps with higher-priority ``MALLOC_CAP_DEFAULT`` are exhausted.
Therefore, under normal conditions ``malloc()`` does not allocate from this pool, but it can fall back to it as a last resort before allocation fails entirely.
.. _external_ram_config_bss: