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.
ESP-IDF has support for the following types of watchdog timers:
.. list:: - Interrupt Watchdog Timer (IWDT) - Task Watchdog Timer (TWDT) :SOC_XT_WDT_SUPPORTED: - Crystal 32K Watchdog Timer (XTWDT)
The various watchdog timers can be enabled using the :ref:`project-configuration-menu`. However, the TWDT can also be enabled during runtime.
{IDF_TARGET_IWDT_TIMER_GROUP:default="Timer Group 1", esp32c2="Timer Group 0"}
The purpose of the IWDT is to ensure that interrupt service routines (ISRs) are not blocked from running for a prolonged period of time (i.e., the IWDT timeout period). Blocking ISRs from running in a timely manner is undesirable as it can increases ISR latency, and also prevents task switching (as task switching is executed form an ISR). The things that can block ISRs from running include:
- Disabling interrupts
- Critical Sections (also disables interrupts)
- Other same/higher priority ISRs (will block same/lower priority ISRs from running it completes execution)
The IWDT utilizes the watchdog timer in {IDF_TARGET_IWDT_TIMER_GROUP} as its underlying hardware timer and leverages the FreeRTOS tick interrupt on each CPU to feed the watchdog timer. If the tick interrupt on a particular CPU is not run at within the IWDT timeout period, it is indicative that something is blocking ISRs from being run on that CPU (see the list of reasons above).
When the IWDT times out, the default action is to invoke the panic handler and display the panic reason as Interrupt wdt timeout on CPU0 or Interrupt wdt timeout on CPU1 (as applicable). Depending on the panic handler's configured behavior (see :ref:`CONFIG_ESP_SYSTEM_PANIC`), users can then debug the source of the IWDT timeout (via the backtrace, OpenOCD, gdbstub etc) or simply reset the chip (which may be preferred in a production environment).
If for whatever reason the panic handler is unable to run after an IWDT timeout, the IWDT has a secondary timeout that will hard-reset the chip (i.e., a system reset).
- The IWDT is enabled by default via the :ref:`CONFIG_ESP_INT_WDT` option.
- The IWDT's timeout is configured by setting the :ref:`CONFIG_ESP_INT_WDT_TIMEOUT_MS` option.
- Note that 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 timeout should always at least twice longer than the period between FreeRTOS ticks (see :ref:`CONFIG_FREERTOS_HZ`).
If you find the IWDT timeout is triggered because an interrupt or critical section is running longer than the timeout period, consider rewriting the code:
- Critical sections should be made as short as possible. Any non-critical code/computation should be placed outside the critical section.
- 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.
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.
{IDF_TARGET_IDLE_TASKS:default="Idle task", esp32="Idle Tasks of each CPU", esp32s3="Idle Tasks of each CPU"}
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.
.. only:: not esp32c2
The TWDT is built around the Hardware Watchdog Timer in Timer Group 0. When a timeout occurs, an interrupt is triggered. Users can define the function `esp_task_wdt_isr_user_handler` in the user code, in order to receive the timeout event and extend the default behavior.
.. only:: esp32c2
The {IDF_TARGET_NAME} has only a single Timer Group, used by Interrupt Watchdog (IWDT). Thus, the Task Watchdog is built around the `esp_timer` component in order to implement a software timer. When a timeout occurs, an interrupt is triggered, notifying the `esp_timer`'s main task. The later will then execute the TWDT callback previously registered. Users can define the function `esp_task_wdt_isr_user_handler` in the user code, in order to receive the timeout event and extend the default behavior.
The following functions can be used to watch tasks using the TWDT:
- :cpp:func:`esp_task_wdt_init` to initialize the TWDT and subscribe the idle tasks.
- :cpp:func:`esp_task_wdt_add` subscribes other tasks to the TWDT.
- Once subscribed, :cpp:func:`esp_task_wdt_reset` should be called from the task to feed the TWDT.
- :cpp:func:`esp_task_wdt_delete()` unsubscribes a previously subscribed task
- :cpp:func:`esp_task_wdt_deinit()` unsubscribes the idle tasks and deinitializes the TWDT
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".
- :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.
- :cpp:func:`esp_task_wdt_reset_user` must be called using the user handle in order to prevent a TWDT timeout.
- :cpp:func:`esp_task_wdt_delete_user` unsubscribes an arbitrary user of the TWDT.
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`.
Note
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:
- Increase :ref:`CONFIG_ESP_TASK_WDT_TIMEOUT_S` in menuconfig for a larger watchdog timeout period.
- You can also call :cpp:func:`esp_task_wdt_init` to increase the watchdog timeout period before erasing a large flash area.
For more information, you can refer to :doc:`SPI Flash <../peripherals/spi_flash/index>`.
The following config options control TWDT configuration. They are all enabled by default:
{IDF_TARGET_IDLE_TASK:default="Idle task", esp32="CPU0 Idle task", esp32s3="CPU0 Idle task"}
.. list::
- :ref:`CONFIG_ESP_TASK_WDT_EN` - enables TWDT feature. If this option is disabled, TWDT cannot be used, even if initialized at runtime.
- :ref:`CONFIG_ESP_TASK_WDT_INIT` - 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`.
- :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.
:not CONFIG_FREERTOS_UNICORE: - :ref:`CONFIG_ESP_TASK_WDT_CHECK_IDLE_TASK_CPU1` - CPU1 Idle task is subscribed to the TWDT during startup.
Note
On a TWDT timeout the default behaviour is to simply print a warning and a backtrace before continuing running the app. If you want a timeout to cause a panic and a system reset then this can be configured through :ref:`CONFIG_ESP_TASK_WDT_PANIC`.
.. only:: SOC_XT_WDT_SUPPORTED
XTAL32K Watchdog Timer (XTWDT)
------------------------------
One of the optional clock inputs to the {IDF_TARGET_NAME} is an external 32 KHz crystal or oscillator (XTAL32K) that is used as a clock source (``XTAL32K_CLK``) to various subsystems (such as the RTC).
The XTWDT is a dedicated watchdog timer used to ensure that the XTAL32K is functioning correctly. When ``XTAL32K_CLK`` works as the clock source of ``RTC_SLOW_CLK`` and stops oscillating, the XTWDT 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.
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.
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.
Configuration
"""""""""""""
- When the external 32KHz crystal or oscillator is selected (:ref:`CONFIG_RTC_CLK_SRC`) the XTWDT can be enabled via the :ref:`CONFIG_ESP_XT_WDT` configuration option.
- The timeout is configured by setting the :ref:`CONFIG_ESP_XT_WDT_TIMEOUT` option.
- The automatic backup clock functionality is enabled via the ref:`CONFIG_ESP_XT_WDT_BACKUP_CLK_ENABLE` configuration option.
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.
A full example using the Task Watchdog is available in esp-idf: :example:`system/task_watchdog`
.. include-build-file:: inc/esp_task_wdt.inc