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5953bca376
This commit moidifies the TWDT as follows: - Adds a feature to allows subscribing arbitrary users to the TWDT - Changes esp_task_wdt_init() API to accept configuration structure - Changes esp_task_wdt_init() and esp_task_wdt_deinit() to subscribe/unsubscribe idle tasks of various cores. - Adds support for SMP FreeRTOS idle tasks - Updates startup code TWDT initialization - Updates API documentation
131 lines
9.0 KiB
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131 lines
9.0 KiB
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Watchdogs
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=========
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Overview
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--------
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The ESP-IDF has support for multiple types of watchdogs, with the two main ones being: The Interrupt Watchdog Timer and the Task Watchdog Timer (TWDT). The Interrupt Watchdog Timer and the TWDT can both be enabled using :ref:`project-configuration-menu`, however the TWDT can also be enabled during runtime. The Interrupt Watchdog is responsible for detecting instances where FreeRTOS task switching is blocked for a prolonged period of time. The TWDT is responsible for detecting instances of tasks running without yielding for a prolonged period.
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Interrupt watchdog
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^^^^^^^^^^^^^^^^^^
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The interrupt watchdog makes sure the FreeRTOS task switching interrupt isn't blocked for a long time. This is bad because no other tasks, including potentially important ones like the WiFi task and the idle task, can't get any CPU runtime. A blocked task switching interrupt can happen because a program runs into an infinite loop with interrupts disabled or hangs in an interrupt.
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The default action of the interrupt watchdog is to invoke the panic handler causing a register dump and an opportunity for the programmer to find out, using either OpenOCD or gdbstub, what bit of code is stuck with interrupts disabled. Depending on the configuration of the panic handler, it can also blindly reset the CPU, which may be preferred in a production environment.
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The interrupt watchdog is built around the hardware watchdog in timer group 1. If this watchdog for some reason cannot execute the NMI handler that invokes the panic handler (e.g. because IRAM is overwritten by garbage), it will hard-reset the SOC. If the panic handler executes, it will display the panic reason as "Interrupt wdt timeout on CPU0" or "Interrupt wdt timeout on CPU1" (as applicable).
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Configuration
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"""""""""""""
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The interrupt watchdog is enabled by default via the :ref:`CONFIG_ESP_INT_WDT` configuration flag. The timeout is configured by setting :ref:`CONFIG_ESP_INT_WDT_TIMEOUT_MS`. The default timeout is higher if PSRAM support is enabled, as a critical section or interrupt routine that accesses a large amount of PSRAM will take longer to complete in some circumstances. The INT WDT timeout should always be longer than the period between FreeRTOS ticks (see :ref:`CONFIG_FREERTOS_HZ`).
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Tuning
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""""""
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If you find the Interrupt watchdog timeout is triggered because an interrupt or critical section is running longer than the timeout period, consider rewriting the code:
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- Critical sections should be made as short as possible. Any non-critical code/computation should be placed outside the critical section.
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- Interrupt handlers should also perform the minimum possible amount of computation. Users can consider deferring any computation to a task by having the ISR push data to a task using queues.
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Neither critical sections or interrupt handlers should ever block waiting for another event to occur. If changing the code to reduce the processing time is not possible or desirable, it's possible to increase the :ref:`CONFIG_ESP_INT_WDT_TIMEOUT_MS` setting instead.
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.. _task-watchdog-timer:
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Task Watchdog Timer
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^^^^^^^^^^^^^^^^^^^
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{IDF_TARGET_IDLE_TASKS:default="Idle task", esp32="Idle Tasks of each CPU"}
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The Task Watchdog Timer (TWDT) is used to monitor particular tasks, ensuring that they are able to execute within a given timeout period. The TWDT primarily watches the {IDF_TARGET_IDLE_TASKS}, however any task can subscribe to be watched by the TWDT. By watching the {IDF_TARGET_IDLE_TASKS}, the TWDT can detect instances of tasks running for a prolonged period of time wihtout yielding. This can be an indicator of poorly written code that spinloops on a peripheral, or a task that is stuck in an infinite loop.
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The TWDT is built around the Hardware Watchdog Timer in Timer Group 0. When a timeout occurs, an interrupt is triggered. Users can redefine the function `esp_task_wdt_isr_user_handler` in the user code, in order to receive the timeout event and handle it differently.
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Usage
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"""""
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The following functions can be used to watch tasks using the TWDT:
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- :cpp:func:`esp_task_wdt_init` to initialize the TWDT and subscribe the idle tasks.
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- :cpp:func:`esp_task_wdt_add` subscribes other tasks to the TWDT.
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- Once subscribed, :cpp:func:`esp_task_wdt_reset` should be called from the task to feed the TWDT.
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- :cpp:func:`esp_task_wdt_delete()` unsubscribes a previously subscribed task
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- :cpp:func:`esp_task_wdt_deinit()` unsubscribes the idle tasks and deinitializes the TWDT
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In the case where applications need to watch at a more granular level (i.e., ensure that a particular functions/stub/code-path is called), the TWDT allows subscription of "users".
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- :cpp:func:`esp_task_wdt_add_user` to subscribe an arbitrary user of the TWDT. This function will return a user handle to the added user.
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- :cpp:func:`esp_task_wdt_reset_user` must be called using the user handle in order to prevent a TWDT timeout.
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- :cpp:func:`esp_task_wdt_delete_user` unsubscribes an arbitrary user of the TWDT.
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Configuration
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"""""""""""""
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The default timeout period for the TWDT is set using config item :ref:`CONFIG_ESP_TASK_WDT_TIMEOUT_S`. This should be set to at least as long as you expect any single task will need to monopolize the CPU (for example, if you expect the app will do a long intensive calculation and should not yield to other tasks). It is also possible to change this timeout at runtime by calling :cpp:func:`esp_task_wdt_init`.
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.. note::
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Erasing large flash areas can be time consuming and can cause a task to run continuously, thus triggering a TWDT timeout. The following two methods can be used to avoid this:
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- Increase :ref:`CONFIG_ESP_TASK_WDT_TIMEOUT_S` in menuconfig for a larger watchdog timeout period.
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- You can also call :cpp:func:`esp_task_wdt_init` to increase the watchdog timeout period before erasing a large flash area.
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For more information, you can refer to :doc:`SPI Flash <../storage/spi_flash>`.
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The following config options control TWDT configuration at startup. They are all enabled by default:
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{IDF_TARGET_IDLE_TASK:default="Idle task", esp32="CPU0 Idle task", esp32s3="CPU0 Idle task"}
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.. list::
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- :ref:`CONFIG_ESP_TASK_WDT` - the TWDT is initialized automatically during startup. If this option is disabled, it is still possible to initialize the Task WDT at runtime by calling :cpp:func:`esp_task_wdt_init`.
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- :ref:`CONFIG_ESP_TASK_WDT_CHECK_IDLE_TASK_CPU0` - {IDF_TARGET_IDLE_TASK} is subscribed to the TWDT during startup. If this option is disabled, it is still possible to subscribe the idle task by calling :cpp:func:`esp_task_wdt_init` again.
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:not CONFIG_FREERTOS_UNICORE: - :ref:`CONFIG_ESP_TASK_WDT_CHECK_IDLE_TASK_CPU1` - CPU1 Idle task is subscribed to the TWDT during startup.
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JTAG and watchdogs
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^^^^^^^^^^^^^^^^^^
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While debugging using OpenOCD, the CPUs will be halted every time a breakpoint is reached. However if the watchdog timers continue to run when a breakpoint is encountered, they will eventually trigger a reset making it very difficult to debug code. Therefore OpenOCD will disable the hardware timers of both the interrupt and task watchdogs at every breakpoint. Moreover, OpenOCD will not reenable them upon leaving the breakpoint. This means that interrupt watchdog and task watchdog functionality will essentially be disabled. No warnings or panics from either watchdogs will be generated when the {IDF_TARGET_NAME} is connected to OpenOCD via JTAG.
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.. only:: SOC_XT_WDT_SUPPORTED
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XTAL32K Watchdog Timer (XTWDT)
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The XTAL32K watchdog makes sure the (optional) external 32 KHz crystal or oscillator is functioning correctly.
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When `XTAL32K_CLK` works as the clock source of `RTC_SLOW_CLK` and stops oscillating, the XTAL32K watchdog timer will detect this and generate an interrupt. It also provides functionality for automatically switching over to the internal, but less accurate oscillator as the `RTC_SLOW_CLK` source.
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Since the switch to the backup clock is done in hardware it can also happen during deep sleep. This means that even if `XTAL32K_CLK` stops functioning while the chip in deep sleep, waiting for a timer to expire, it will still be able to wake-up as planned.
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If the `XTAL32K_CLK` starts functioning normally again, you can call `esp_xt_wdt_restore_clk` to switch back to this clock source and re-enable the watchdog timer.
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Configuration
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"""""""""""""
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When the external 32KHz crystal or oscillator is selected (:ref:`CONFIG_RTC_CLK_SRC`) the XTAL32K watchdog can be enabled via the :ref:`CONFIG_ESP_XT_WDT` configuration flag. The timeout is configured by setting :ref:`CONFIG_ESP_XT_WDT_TIMEOUT`. The automatic backup clock functionality is enabled via the ref:`CONFIG_ESP_XT_WDT_BACKUP_CLK_ENABLE` configuration.
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Interrupt Watchdog API Reference
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--------------------------------
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Header File
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^^^^^^^^^^^
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* :component_file:`esp_system/include/esp_int_wdt.h`
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Functions
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---------
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.. doxygenfunction:: esp_int_wdt_init
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Task Watchdog API Reference
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----------------------------
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A full example using the Task Watchdog is available in esp-idf: :example:`system/task_watchdog`
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.. include-build-file:: inc/esp_task_wdt.inc
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