72 lines
3.5 KiB
ReStructuredText
72 lines
3.5 KiB
ReStructuredText
Watchdogs
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=========
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Overview
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--------
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Esp-idf has support for two types of watchdogs: a task watchdog as well as an interrupt watchdog. Both can be
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enabled using ``make menuconfig`` and selecting the appropriate options.
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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
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is bad because no other tasks, including potentially important ones like the WiFi task and the idle task,
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can't get any CPU runtime. A blocked task switching interrupt can happen because a program runs into an
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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
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for the programmer to find out, using either OpenOCD or gdbstub, what bit of code is stuck with interrupts
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disabled. Depending on the configuration of the panic handler, it can also blindly reset the CPU, which may be
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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
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cannot execute the NMI handler that invokes the panic handler (e.g. because IRAM is overwritten by garbage),
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it will hard-reset the SOC.
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Task watchdog
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^^^^^^^^^^^^^
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Any tasks can elect to be watched by the task watchdog. If such a task does not feed the watchdog within the time
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specified by the task watchdog timeout (which is configurable using ``make menuconfig``), the watchdog will
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print out a warning with information about which processes are running on the ESP32 CPUs and which processes
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failed to feed the watchdog.
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By default, the task watchdog watches the idle tasks. The usual cause of idle tasks not feeding the watchdog
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is a higher-priority process looping without yielding to the lower-priority processes, and can be an indicator
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of badly-written code that spinloops on a peripheral or a task that is stuck in an infinite loop.
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Other task can elect to be watched by the task watchdog by calling ``esp_task_wdt_feed()``. Calling this routine
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for the first time will register the task to the task watchdog; calling it subsequent times will feed
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the watchdog. If a task does not want to be watched anymore (e.g. because it is finished and will call
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``vTaskDelete()`` on itself), it needs to call ``esp_task_wdt_delete()``.
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The task watchdog is built around the hardware watchdog in timer group 0. If this watchdog for some reason
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cannot execute the interrupt handler that prints the task data (e.g. because IRAM is overwritten by garbage
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or interrupts are disabled entirely) it will hard-reset the SOC.
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JTAG and watchdogs
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^^^^^^^^^^^^^^^^^^
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While debugging using OpenOCD, if the CPUs are halted the watchdogs will keep running, eventually resetting the
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CPU. This makes it very hard to debug code; that is why the OpenOCD config will disable both watchdogs on startup.
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This does mean that you will not get any warnings or panics from either the task or interrupt watchdog when the ESP32
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is connected to OpenOCD via JTAG.
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API Reference
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-------------
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Header Files
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^^^^^^^^^^^^
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* `esp32/include/esp_int_wdt.h <https://github.com/espressif/esp-idf/blob/master/components/esp32/include/esp_int_wdt.h>`_
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* `esp32/include/esp_task_wdt.h <https://github.com/espressif/esp-idf/blob/master/components/esp32/include/esp_task_wdt.h>`_
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Functions
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---------
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.. doxygenfunction:: esp_int_wdt_init
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.. doxygenfunction:: esp_task_wdt_init
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.. doxygenfunction:: esp_task_wdt_feed
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.. doxygenfunction:: esp_task_wdt_delete
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