24 lines
1.5 KiB
ReStructuredText
24 lines
1.5 KiB
ReStructuredText
* Regarding stacks in PSRAM: For tasks not calling on code in ROM in any way, directly or indirectly, the menuconfig option :ref:`CONFIG_SPIRAM_ALLOW_STACK_EXTERNAL_MEMORY` will eliminate the check in xTaskCreateStatic, allowing a task's stack to be in external RAM. Using this is not advised, however.
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* When used at 80 MHz clock speed, external RAM must also occupy either the HSPI or VSPI bus. Select which SPI host will be used by :ref:`CONFIG_SPIRAM_OCCUPY_SPI_HOST`.
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Chip revisions
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==============
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There are some issues with certain revisions of ESP32 that have repercussions for use with external RAM. The issues are documented in the `ESP32 ECO`_ document. In particular, ESP-IDF handles the bugs mentioned in the following ways:
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ESP32 rev v0
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------------
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ESP-IDF has no workaround for the bugs in this revision of silicon, and it cannot be used to map external PSRAM into ESP32's main memory map.
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ESP32 rev v1
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------------
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The bugs in this revision of silicon cause issues if certain sequences of machine instructions operate on external memory. (`ESP32 ECO`_ 3.2). As a workaround, the GCC compiler received the flag ``-mfix-esp32-psram-cache-issue`` to filter these sequences and only output the code that can safely be executed. Enable this flag by checking :ref:`CONFIG_SPIRAM_CACHE_WORKAROUND`.
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Aside from linking to a recompiled version of Newlib with the additional flag, ESP-IDF also does the following:
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- Avoids using some ROM functions
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- Allocates static memory for the WiFi stack
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