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docs: add note for MALLOC_CAP_DMA for ESP32-S2 according to customer feedback

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Shang Zhou 2022-01-11 17:17:25 +08:00
parent 9373bdfe2f
commit 4d9db3382e
2 changed files with 11 additions and 3 deletions
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6
docs/en/api-guides/external-ram.rst
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@ -129,7 +129,11 @@ External RAM use has the following restrictions:
* When flash cache is disabled (for example, if the flash is being written to), the external RAM also becomes inaccessible; any reads from or writes to it will lead to an illegal cache access exception. This is also the reason why ESP-IDF does not by default allocate any task stacks in external RAM (see below).
* External RAM cannot be used as a place to store DMA transaction descriptors or as a buffer for a DMA transfer to read from or write into. Any buffers that will be used in combination with DMA must be allocated using ``heap_caps_malloc(size, MALLOC_CAP_DMA)`` and can be freed using a standard ``free()`` call.
* External RAM cannot be used as a place to store DMA transaction descriptors or as a buffer for a DMA transfer to read from or write into. Therefore when External RAM is enabled, any buffers that will be used in combination with DMA must be allocated using ``heap_caps_malloc(size, MALLOC_CAP_DMA | MALLOC_CAP_INTERNAL)`` and can be freed using a standard ``free()`` call.
.. only:: SOC_PSRAM_DMA_CAPABLE
Note, although {IDF_TARGET_NAME} has hardware support for DMA to/from external RAM, this is not yet supported in ESP-IDF.
* External RAM uses the same cache region as the external flash. This means that frequently accessed variables in external RAM can be read and modified almost as quickly as in internal ram. However, when accessing large chunks of data (>32 KB), the cache can be insufficient, and speeds will fall back to the access speed of the external RAM. Moreover, accessing large chunks of data can "push out" cached flash, possibly making the execution of code slower afterwards.

8
docs/zh_CN/api-guides/external-ram.rst
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@ -129,9 +129,13 @@ ESP-IDF 启动过程中，片外 RAM 被映射到以 {IDF_TARGET_PSRAM_ADDR_STAR
* Flash cache 禁用时（比如，正在写入 flash），片外 RAM 将无法访问；同样，对片外 RAM 的读写操作也将导致 cache 访问异常。出于这个原因，ESP-IDF 不会在片外 RAM 中分配任务堆栈（详见下文）。
* 片外 RAM 不能用于储存 DMA 事务描述符，也不能用作 DMA 读写操作的缓冲区 (Buffer)。与 DMA 搭配使用的 Buffer 必须先使用 ``heap_caps_malloc(size, MALLOC_CAP_DMA)`` 进行分配，之后可以调用标准 ``free()`` 回调释放 Buffer。
* 片外 RAM 不能用于储存 DMA 事务描述符，也不能用作 DMA 读写操作的缓冲区 (Buffer)。因此，当片外 RAM 启用时，与 DMA 搭配使用的 Buffer 必须先使用 ``heap_caps_malloc(size, MALLOC_CAP_DMA | MALLOC_CAP_INTERNAL)`` 进行分配，之后可以调用标准 ``free()`` 回调释放 Buffer。
* 片外 RAM 与片外 flash 使用相同的 cache 区域，这意味着频繁在片外 RAM 访问的变量可以像在片上 RAM 中一样快速读取和修改。但访问大块数据时（大于 32 KB），cache 空间可能会不足，访问速度将回落到片外 RAM 访问速度。此外，访问大块数据会挤出 flash cache，可能降低代码执行速度。
.. only:: SOC_PSRAM_DMA_CAPABLE
注意，尽管 {IDF_TARGET_NAME} 中已有硬件支持 DMA 与片外 RAM，但在 ESP-IDF 中，尚未提供软件支持。
* 片外 RAM 与片外 flash 使用相同的 cache 区域，这意味着频繁在片外 RAM 访问的变量可以像在片上 RAM 中一样快速读取和修改。但访问大块数据时（大于 32 KB），cache 空间可能会不足，访问速度将回落到片外 RAM 访问速度。此外，访问大块数据会挤出 flash cache，可能降低代码执行速度。
* 一般来说，片外 RAM 不可用作任务堆栈存储器。因此 :cpp:func:`xTaskCreate` 及类似函数将始终为堆栈和任务 TCB 分配片上储存器，而 :cpp:func:`xTaskCreateStatic` 类型的函数将检查传递的 Buffer 是否属于片上存储器。