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Fix example code, add chapter to docs about interrupts and multicore issues

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This commit is contained in:
Jeroen Domburg
2016-12-08 14:42:00 +08:00
parent cb9ef19d3b
commit baa6a477c5
5 changed files with 34 additions and 7 deletions
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27
docs/api/intr_alloc.rst
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@@ -29,7 +29,33 @@ interrupt for DevA is still pending, but because the int line never went low (De
even when the int for DevB was cleared) the interrupt is never serviced.)
Multicore issues
----------------
Peripherals that can generate interrupts can be divided in two types: external peripherals, outside the Xtensa
cores in the ESP32, and internal peripherals, inside the ESP32. Interrupt handling differs slightly between
these two types of peripherals.
Each Xtensa core has its own set of internal peripherals: three timer comparators, a performance monitor and two
software interrupts. These peripherals can only be configured from the core they are associated with. When
generating an interrupt, the interrupt they generate is hard-wired to their associated core; it's not possible
to have e.g. an internal timer comparator of one core generate an interrupt on another core. That is why these
sources can only be managed using a task running on that specific core. Internal interrupt sources are still
allocatable using esp_intr_alloc as normal, but they cannot be shared and will always have a fixed interrupt
level (namely, the one associated in hardware with the peripheral). Internal interrupt sources are defined
in esp_intr_alloc.h as ETS_INTERNAL_*_INTR_SOURCE.
The remaining interrupt slots in both cores are wired to an interrupt multiplexer, which can be used to
route any external interrupt source to any of these interrupt slots. Allocating an external interrupt will always
allocate it on the core that does the allocation, and freeing the interrupt should always happen on the same
core. Disabling and enabling the interrupt from another core is allowed, however. External interrupts can
share an interrupt slot bu passing ESP_INTR_FLAG_SHARED as a flag to esp_intr_alloc. External interrupt sources
are defined in soc/soc.h as ETS_*_INTR_SOURCE.
Care should be taken when allocating an interrupt using a task not pinned to a certain core; while running
code not in a critical secion, these tasks can migrate between cores at any moment, possibly making an
interrupt operation fail because of the reasons mentioned above. It is advised to always use
xTaskCreatePinnedToCore with a specific CoreID argument to create tasks that will handle interrupts.
Application Example
-------------------
@@ -58,6 +84,7 @@ Macros
.. doxygendefine:: ESP_INTR_FLAG_SHARED
.. doxygendefine:: ESP_INTR_FLAG_EDGE
.. doxygendefine:: ESP_INTR_FLAG_IRAM
.. doxygendefine:: ESP_INTR_FLAG_INTRDISABLED
Type Definitions
^^^^^^^^^^^^^^^^