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91 lines
5.0 KiB
ReStructuredText
91 lines
5.0 KiB
ReStructuredText
High-Level Interrupts
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=====================
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.. toctree::
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:maxdepth: 1
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The Xtensa architecture has support for 32 interrupts, divided over 7 levels (levels 1 to 7, with 7 being an NMI), plus an assortment of exceptions. On the {IDF_TARGET_NAME}, the interrupt mux allows most interrupt sources to be routed to these interrupts using the :doc:`interrupt allocator <../api-reference/system/intr_alloc>`. Normally, interrupts will be written in C, but ESP-IDF allows high-level interrupts to be written in assembly as well, resulting in very low interrupt latencies.
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Interrupt Levels
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----------------
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.. only:: esp32
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===== ================= ====================================================
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Level Symbol Remark
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===== ================= ====================================================
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1 N/A Exception and level 0 interrupts. Handled by ESP-IDF
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2-3 N/A Medium level interrupts. Handled by ESP-IDF
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4 xt_highint4 Free to use :ref:`(See 1) <hlinterrupts-pin-notes>`
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5 xt_highint5 Normally used by ESP-IDF debug logic :ref:`(See 1) <hlinterrupts-pin-notes>`
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NMI xt_nmi Free to use
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dbg xt_debugexception Debug exception. Called on e.g. a BREAK instruction. :ref:`(See 2) <hlinterrupts-pin-notes>`
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===== ================= ====================================================
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.. _hlinterrupts-pin-notes:
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The following notes give more information about the items in the tables above.
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1. ESP-IDF debug logic can be configured to run on `xt_highint4` or `xt_highint5` in :ref:`CONFIG_ESP_SYSTEM_CHECK_INT_LEVEL`. Bluetooth's interrupt can be configured to run on level 4 by enabling :ref:`CONFIG_BTDM_CTRL_HLI`. If :ref:`CONFIG_BTDM_CTRL_HLI` is enabled, ESP-IDF debug logic must be running on level 5 interrupt.
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2. If :ref:`CONFIG_BTDM_CTRL_HLI` is enabled, `xt_debugexception` is used to fix `live lock issue <https://www.espressif.com/sites/default/files/documentation/eco_and_workarounds_for_bugs_in_esp32_en.pdf>`_ in ESP32 ECO3.
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.. only:: not esp32
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===== ================= ====================================================
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Level Symbol Remark
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===== ================= ====================================================
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1 N/A Exception and level 0 interrupts. Handled by ESP-IDF
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2-3 N/A Medium level interrupts. Handled by ESP-IDF
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4 xt_highint4 Normally used by ESP-IDF debug logic
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5 xt_highint5 Free to use
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NMI xt_nmi Free to use
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dbg xt_debugexception Debug exception. Called on e.g. a BREAK instruction.
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===== ================= ====================================================
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Using these symbols is done by creating an assembly file (suffix .S) and defining the named symbols, like this::
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.section .iram1,"ax"
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.global xt_highint5
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.type xt_highint5,@function
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.align 4
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xt_highint5:
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... your code here
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rsr a0, EXCSAVE_5
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rfi 5
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For a real-life example, see the :component_file:`esp_system/port/soc/{IDF_TARGET_PATH_NAME}/highint_hdl.S` file; the panic handler interrupt is implemented there.
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Notes
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-----
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- Do not call C code from a high-level interrupt; as these interrupts are run from a critical section, this can cause the target to crash.
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Note that although the panic handler interrupt does call normal C code, this exception is allowed due to the fact that this handler never returns (i.e., the application will not continue to run after the panic handler).
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so breaking C code execution flow is not a problem.
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.. only:: esp32
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When :ref:`CONFIG_BTDM_CTRL_HLI` is enabled, C code is also called from a high-level interrupt, this is possible thanks to some additional protection added to it.
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- Make sure your assembly code gets linked in. Indeed, as the free-to-use symbols are declared as weak, the linker may discard the file containing the symbol. This will
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happen if the only symbol defined, or used, from the user file is the ``xt_*`` free-to-use symbol. To avoid this, in the assembly file containing the ``xt_*`` symbol,
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define another symbol, like::
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.global ld_include_my_isr_file
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ld_include_my_isr_file:
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Here it is called ``ld_include_my_isr_file`` but can have any name, as long as it is not defined anywhere else in the project.
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Then, in the component ``CMakeLists.txt``, add this name as an unresolved symbol to the ld command line arguments::
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target_link_libraries(${COMPONENT_TARGET} "-u ld_include_my_isr_file")
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This should cause the linker to always include the file defining ``ld_include_my_isr_file``, causing the ISR to always be linked in.
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- High-level interrupts can be routed and handled using :cpp:func:`esp_intr_alloc` and associated functions. The handler and handler arguments
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to :cpp:func:`esp_intr_alloc` must be NULL, however.
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- In theory, medium priority interrupts could also be handled in this way. ESP-IDF does not support this yet.
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