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111 lines
6.6 KiB
ReStructuredText
111 lines
6.6 KiB
ReStructuredText
Timer
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=====
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:link_to_translation:`zh_CN:[中文]`
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Introduction
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------------
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The ESP32 chip contains two hardware timer groups. Each group has two general-purpose hardware timers. They are all 64-bit generic timers based on 16-bit prescalers and 64-bit up / down counters which are capable of being auto-reloaded.
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Functional Overview
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-------------------
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The following sections of this document cover the typical steps to configure and operate a timer:
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* :ref:`timer-api-timer-initialization` - covers which parameters should be set up to get the timer working, and also what specific functionality is provided depending on the timer configuration.
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* :ref:`timer-api-timer-control` - describes how to read a timer's value, pause or start a timer, and change how it operates.
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* :ref:`timer-api-alarms` - shows how to set and use alarms.
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* :ref:`timer-api-interrupts`- explains how to enable and use interrupts.
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.. _timer-api-timer-initialization:
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Timer Initialization
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^^^^^^^^^^^^^^^^^^^^
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The two ESP32 timer groups, with two timers in each, provide the total of four individual timers for use. An ESP32 timer group should be identified using :cpp:type:`timer_group_t`. An individual timer in a group should be identified with :cpp:type:`timer_idx_t`.
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First of all, the timer should be initialized by calling the function :cpp:func:`timer_init` and passing a structure :cpp:type:`timer_config_t` to it to define how the timer should operate. In particular, the following timer parameters can be set:
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* **Divider**: Sets how quickly the timer's counter is "ticking". The setting :cpp:member:`divider` is used as a divisor of the incoming 80 MHz APB_CLK clock.
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* **Mode**: Sets if the counter should be incrementing or decrementing. It can be defined using :cpp:member:`counter_dir` by selecting one of the values from :cpp:type:`timer_count_dir_t`.
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* **Counter Enable**: If the counter is enabled, it will start incrementing / decrementing immediately after calling :cpp:func:`timer_init`. You can change the behavior with :cpp:member:`counter_en` by selecting one of the values from :cpp:type:`timer_start_t`.
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* **Alarm Enable**: Can be set using :cpp:member:`alarm_en`.
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* **Auto Reload**: Sets if the counter should :cpp:member:`auto_reload` the initial counter value on the timer's alarm or continue incrementing or decrementing.
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* **Interrupt Type**: Select which interrupt type should be triggered on the timer's alarm. Set the value defined in :cpp:type:`timer_intr_mode_t`.
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To get the current values of the timer's settings, use the function :cpp:func:`timer_get_config`.
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.. _timer-api-timer-control:
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Timer Control
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^^^^^^^^^^^^^
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Once the timer is enabled, its counter starts running. To enable the timer, call the function :cpp:func:`timer_init` with :cpp:member:`counter_en` set to ``true``, or call :cpp:func:`timer_start`. You can specify the timer's initial counter value by calling :cpp:func:`timer_set_counter_value`. To check the timer's current value, call :cpp:func:`timer_get_counter_value` or :cpp:func:`timer_get_counter_time_sec`.
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To pause the timer at any time, call :cpp:func:`timer_pause`. To resume it, call :cpp:func:`timer_start`.
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To reconfigure the timer, you can call :cpp:func:`timer_init`. This function is described in Section :ref:`timer-api-timer-initialization`.
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You can also reconfigure the timer by using dedicated functions to change individual settings:
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============= =================================== ==========================================================================
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Setting Dedicated Function Description
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============= =================================== ==========================================================================
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Divider :cpp:func:`timer_set_divider` Change the rate of ticking. To avoid unpredictable results, the timer should be paused when changing the divider. If the timer is running, :cpp:func:`timer_set_divider` pauses it, change the setting, and start the timer again.
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Mode :cpp:func:`timer_set_counter_mode` Set if the counter should be incrementing or decrementing
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Auto Reload :cpp:func:`timer_set_auto_reload` Set if the initial counter value should be reloaded on the timer's alarm
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============= =================================== ==========================================================================
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.. _timer-api-alarms:
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Alarms
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^^^^^^
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To set an alarm, call the function :cpp:func:`timer_set_alarm_value` and then enable the alarm using :cpp:func:`timer_set_alarm`. The alarm can also be enabled during the timer initialization stage, when :cpp:func:`timer_init` is called.
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After the alarm is enabled, and the timer reaches the alarm value, the following two actions can occur depending on the configuration:
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* An interrupt will be triggered if previously configured. See Section :ref:`timer-api-interrupts` on how to configure interrupts.
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* When :cpp:member:`auto_reload` is enabled, the timer's counter will automatically be reloaded to start counting again from a previously configured value. This value should be set in advance with :cpp:func:`timer_set_counter_value`.
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.. note::
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* If an alarm value is set and the timer has already reached this value, the alarm is triggered immediately.
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* Once triggered, the alarm is disabled automatically and needs to be re-enabled to trigger again.
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To check the specified alarm value, call :cpp:func:`timer_get_alarm_value`.
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.. _timer-api-interrupts:
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Interrupts
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^^^^^^^^^^
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Registration of the interrupt handler for a specific timer or a timer group can be done by calling :cpp:func:`timer_isr_register`.
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To enable interrupts for a timer group, call :cpp:func:`timer_group_intr_enable`, for a specific timer call :cpp:func:`timer_enable_intr`.
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To disable interrupts for a timer group, call :cpp:func:`timer_group_intr_disable`, for a specified timer, call :cpp:func:`timer_disable_intr`.
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When handling an interrupt within an interrupt serivce routine (ISR), the interrupt status bit needs to be explicitly cleared. To do that, set the ``TIMERGN.int_clr_timers.tM`` structure, defined in :component_file:`soc/esp32/include/soc/timer_group_struct.h`. In this structure, ``N`` is the timer group number [0, 1], ``M`` is the timer number [0, 1]. For example, to clear an interrupt status bit for the timer 1 in the timer group 0, call the following::
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TIMERG0.int_clr_timers.t1 = 1
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For more information on how to use interrupts, please see the application example below.
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Application Example
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-------------------
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The 64-bit hardware timer example: :example:`peripherals/timer_group`.
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API Reference
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-------------
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.. include:: /_build/inc/timer.inc
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.. include:: /_build/inc/timer_types.inc
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