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Merge pull request #484 from david-cermak/fix/modem_docs_ota
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fix(modem): Documented some tips on failing OTA
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david-cermak authored Jan 18, 2024
2 parents 7b77794 + adde6df commit efa26b7
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15 changes: 13 additions & 2 deletions docs/esp_modem/en/README.rst
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Expand Up @@ -120,6 +120,7 @@ Switching between manual modes
The diagram below depicts allowed transitions between manual CMUX modes

::

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Known issues
------------

There are certain issues, especially in using CMUX mode which you can
experience with some devices:
There are certain typical issues you might experience when working with esp_modem. This section elaborates on these problems and offers workarounds.

When using UART terminal, you might find running OTA over https quite unstable, exhibiting frequent UART buffer overflows.
The reason for that is that ESP32's UART is interrupt driven, so while performing computational extensive tasks with TLS session,
we need to timely interrupt to process incoming data. Here'are few suggestions to mitigate the impact:
* Move UART ISR to IRAM
* Increase internal UART rx buffer size
* Increase UART terminal task priority
* Use UART flow control
If none of the above helps, you can check the test ``target_ota``, which performs OTA in two steps -- first read the data, then pass the data to mbedTLS. See the test ``README.md`` for more details.

Potential issues when using CMUX mode and these devices:

1) Some modems (e.g. A76xx serries) use 2 bytes CMUX payload, which
might cause buffer overflow when trying to defragment the payload.
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