-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:
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:
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:
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
projects / esp-idf / commitdiff