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Review the file api-reference/peripherals/timer.rst

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docs/en/api-reference/peripherals/timer.rst
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TIMER
Timer
=====
Introduction
------------
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 auto-reload-capable up / down counters.
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.
Functional Overview
-------------------
Typical steps to configure an operate the timer are described in the following sections:
The following sections of this document cover the typical steps to configure and operate a timer:
* :ref:`timer-api-timer-initialization` - what parameters should be set up to get the timer working and what specific functionality is provided depending on the set up.
* :ref:`timer-api-timer-control` - how to read the timer's value, pause / start the timer, and change how it operates.
* :ref:`timer-api-alarms` - setting and using alarms.
* :ref:`timer-api-interrupts`- how to enable and use interrupts.
* :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.
* :ref:`timer-api-timer-control` - describes how to read a timer's value, pause or start a timer, and change how it operates.
* :ref:`timer-api-alarms` - shows how to set and use alarms.
* :ref:`timer-api-interrupts`- explains how to enable and use interrupts.
.. _timer-api-timer-initialization:
@ -23,18 +23,18 @@ Typical steps to configure an operate the timer are described in the following s
Timer Initialization
^^^^^^^^^^^^^^^^^^^^
The two timer groups on-board of the ESP32 are identified using :cpp:type:`timer_group_t`. Individual timers in a group are identified with :cpp:type:`timer_idx_t`. The two groups, each having two timers, provide the total of four individual timers to our disposal.
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`.
Before starting the timer, it should be initialized by calling :cpp:func:`timer_init`. This function should be provided with a structure :cpp:type:`timer_config_t` to define how timer should operate. In particular the following timer's parameters may be set:
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:
* **Divider**: How quickly the timer's counter is "ticking". This depends on the setting of :cpp:member:`divider`, that will be used as divisor of the incoming 80 MHz APB_CLK clock.
* **Mode**: If the the counter is incrementing or decrementing, defined using :cpp:member:`counter_dir` by selecting one of values from :cpp:type:`timer_count_dir_t`.
* **Counter Enable**: If the counter is enabled, then it will start incrementing / decrementing immediately after calling :cpp:func:`timer_init`. This action is set using :cpp:member:`counter_en` by selecting one of vales from :cpp:type:`timer_start_t`.
* **Alarm Enable**: Determined by the setting of :cpp:member:`alarm_en`.
* **Auto Reload**: Whether the counter should :cpp:member:`auto_reload` a specific initial value on the timer's alarm, or continue incrementing or decrementing.
* **Interrupt Type**: Whether an interrupt is triggered on timer's alarm. Set the value defined in :cpp:type:`timer_intr_mode_t`.
* **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.
* **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`.
* **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`.
* **Alarm Enable**: Can be set using :cpp:member:`alarm_en`.
* **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.
* **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`.
To get the current values of the timers settings, use function :cpp:func:`timer_get_config`.
To get the current values of the timer's settings, use the function :cpp:func:`timer_get_config`.
.. _timer-api-timer-control:
@ -42,35 +42,40 @@ To get the current values of the timers settings, use function :cpp:func:`timer_
Timer Control
^^^^^^^^^^^^^
Once the timer is configured and enabled, it is already "ticking". To check it's current value call :cpp:func:`timer_get_counter_value` or :cpp:func:`timer_get_counter_time_sec`. To set the timer to specific starting value call :cpp:func:`timer_set_counter_value`.
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`.
The timer may be paused at any time by calling :cpp:func:`timer_pause`. To start it again call :cpp:func:`timer_start`.
To pause the timer at any time, call :cpp:func:`timer_pause`. To resume it, call :cpp:func:`timer_start`.
To change how the timer operates you can call once more :cpp:func:`timer_init` described in section :ref:`timer-api-timer-initialization`. Another option is to use dedicated functions to change individual settings:
To reconfigure the timer, you can call :cpp:func:`timer_init`. This function is described in Section :ref:`timer-api-timer-initialization`.
* **Divider** value - :cpp:func:`timer_set_divider`. **Note:** the timer should be paused when changing the divider to avoid unpredictable results. If the timer is already running, :cpp:func:`timer_set_divider` will first pause the timer, change the divider, and finally start the timer again.
* **Mode** (whether the counter incrementing or decrementing) - :cpp:func:`timer_set_counter_mode`
* **Auto Reload** counter on alarm - :cpp:func:`timer_set_auto_reload`
You can also reconfigure the timer by using dedicated functions to change individual settings:
============= =================================== ==========================================================================
Setting Dedicated Function Description
============= =================================== ==========================================================================
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.
Mode :cpp:func:`timer_set_counter_mode` Set if the counter should be incrementing or decrementing
Auto Reload :cpp:func:`timer_set_auto_reload` Set if the initial counter value should be reloaded on the timer's alarm
============= =================================== ==========================================================================
.. _timer-api-alarms:
Alarms
^^^^^^
To set an alarm, call function :cpp:func:`timer_set_alarm_value` and then enable it with :cpp:func:`timer_set_alarm`. The alarm may be also enabled during the timer initialization stage, when :cpp:func:`timer_init` is called.
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.
After the alarm is enabled and the timer reaches the alarm value, depending on configuration, the following two actions may happen:
After the alarm is enabled, and the timer reaches the alarm value, the following two actions can occur depending on the configuration:
* An interrupt will be triggered, if previously configured. See section :ref:`timer-api-interrupts` how to configure interrupts.
* When :cpp:member:`auto_reload` is enabled, the timer's counter will be reloaded to start counting from specific initial value. The value to start should be set in advance with :cpp:func:`timer_set_counter_value`.
* An interrupt will be triggered if previously configured. See Section :ref:`timer-api-interrupts` on how to configure interrupts.
* 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`.
.. note::
* The alarm will be triggered immediately, if an alarm value is set and the timer has already passed this value.
* Once triggered the alarm will be disabled automatically and needs to be re-armed to trigger again.
* If an alarm value is set and the timer has already reached this value, the alarm is triggered immediately.
* Once triggered, the alarm is disabled automatically and needs to be re-enabled to trigger again.
To check what alarm value has been set up, call :cpp:func:`timer_get_alarm_value`.
To check the specified alarm value, call :cpp:func:`timer_get_alarm_value`.
.. _timer-api-interrupts:
@ -78,15 +83,16 @@ To check what alarm value has been set up, call :cpp:func:`timer_get_alarm_value
Interrupts
^^^^^^^^^^
Registration of the interrupt handler for a specific timer group and timer is done be calling :cpp:func:`timer_isr_register`.
Registration of the interrupt handler for a specific timer or a timer group can be done by calling :cpp:func:`timer_isr_register`.
To enable interrupts for a timer group call :cpp:func:`timer_group_intr_enable`. To do it for a specific timer, call :cpp:func:`timer_enable_intr`. Disabling of interrupts is done with corresponding functions :cpp:func:`timer_group_intr_disable` and :cpp:func:`timer_disable_intr`.
To enable interrupts for a timer group, call :cpp:func:`timer_group_intr_enable`, for a specific timer call :cpp:func:`timer_enable_intr`.
To disable interrupts for a timer group, call :cpp:func:`timer_group_intr_disable`, for a specified timer, call :cpp:func:`timer_disable_intr`.
When servicing an interrupt within an ISR, the interrupt need to explicitly cleared. To do so, set the ``TIMERGN.int_clr_timers.tM`` structure defined in :component_file:`soc/esp32/include/soc/timer_group_struct.h`, where N is the timer group number [0, 1] and M is the timer number [0, 1]. For example to clear an interrupt for the timer 1 in the timer group 0, call the following::
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::
TIMERG0.int_clr_timers.t1 = 1
See the application example below how to use interrupts.
For more information on how to use interrupts, please see the application example below.
Application Example