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doc: API reference for GPTimer
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docs/en/api-reference/peripherals/gptimer.rst
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docs/en/api-reference/peripherals/gptimer.rst
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General Purpose Timer (GPTimer)
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===============================
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Introduction
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------------
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A general purpose timer is a hardware timer with high resolution and flexible alarm action. The behavior when the internal counter of a timer reaches a specific target value is called timer alarm. When a timer alarms, a user registered per-timer callback would be called.
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Typically, a general purpose timer can be used in scenarios like:
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- Free running as a wall clock, fetching a high-resolution time stamp at any time and any places
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- Generate period alarms, trigger events periodically
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- Generate one-shot alarm, respond in target time
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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 install and operate a timer:
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- `Resource Allocation <#resource-allocation>`__ - covers which parameters should be set up to get a timer handle and how to recycle the resources when GPTimer finishes working.
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- `Set and Get count value <#set-and-get-count-value>`__ - covers how to force the timer counting from a start point and how to get the count value at anytime.
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- `Start and Stop timer <#start-and-stop-timer>`__ - covers which parameters should be set up to start the timer with specific alarm event behavior.
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- `Power Management <#power-management>`__ - describes how different source clock selections can affect power consumption.
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- `IRAM safe <#iram-safe>`__ - describes tips on how to make the timer interrupt and IO control functions work better along with a disabled cache.
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Resource Allocation
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^^^^^^^^^^^^^^^^^^^
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Different ESP chip might have different number of independent timer groups, and within each group, there could also be several independent timers. Refer to the datasheet to find out how many hardware timers exist (usually described in the "General Purpose Timer" chapter).
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From driver's point of view, a GPTimer instance is represented by :cpp:type:`gptimer_handle_t`. The driver behind will manage all available hardware resources in a pool, so that users don't need to care about which timer and which group it belongs to.
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To install a timer instance, there's a configuration structure that needs to be given in advance: :cpp:type:`gptimer_config_t`:
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- :cpp:member:`clk_src` selects the source clock for the timer. The available clocks are listed in :cpp:type:`gptimer_clock_source_t`, [1]_ you can only pick one of them. For the effect on power consumption of different clock source, please refer to `Power management <#power-management>`__ section.
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- :cpp:member:`direction` sets the counting direction of the timer, supported directions are listed in :cpp:type:`gptimer_count_direction_t`, you can only pick one of them.
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- :cpp:member:`resolution_hz` sets the resolution of the internal counter. Each count step is equivalent to **1 / resolution_hz** seconds.
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- Optional :cpp:member:`intr_shared` sets whether or not mark the timer interrupt source as a shared one. For the pros/cons of a shared interrupt, you can refer to :doc:`Interrupt Handling <../../api-reference/system/intr_alloc>`.
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With all the above configurations set in the structure, the structure can be passed to :cpp:func:`gptimer_new_timer` which will instantiate the timer instance and return a handle of the timer.
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The function can fail due to various errors such as insufficient memory, invalid arguments, etc. Specifically, when there are no more free timers (i.e. all hardware resources have been used up), then :cpp:member:`ESP_ERR_NOT_FOUND` will be returned. The total number of available timers is represented by the :c:macro:`SOC_TIMER_GROUP_TOTAL_TIMERS` and its value will depend on the ESP chip.
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If a previously created GPTimer instance is no longer required, you should recycle the timer by calling :cpp:func:`gptimer_del_timer`. This will allow the underlying HW timer to be used for other purposes. Before deleting a GPTimer handle, you should stop it by :cpp:func:`gptimer_stop` in advance or make sure it has not started yet by :cpp:func:`gptimer_start`.
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Creating a GPTimer Handle with Resolution of 1MHz
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. code:: c
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gptimer_handle_t gptimer = NULL;
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gptimer_config_t timer_config = {
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.clk_src = GPTIMER_CLK_SRC_APB,
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.direction = GPTIMER_COUNT_UP,
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.resolution_hz = 1 * 1000 * 1000, // 1MHz, 1 tick = 1us
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};
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ESP_ERROR_CHECK(gptimer_new_timer(&timer_config, &gptimer));
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Set and Get Count Value
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^^^^^^^^^^^^^^^^^^^^^^^
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When the GPTimer is created, the internal counter will be reset to zero by default. The counter value can be updated asynchronously by :cpp:func:`gptimer_set_raw_count`. The maximum count value is dependent on the hardware timer's bit-width, which is also reflected by the SOC macro :c:macro:`SOC_TIMER_GROUP_COUNTER_BIT_WIDTH`. When updating the raw count of an active timer, the timer will immediately start counting from the new value.
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Count value can be retrieved by :cpp:func:`gptimer_get_raw_count`, at anytime.
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Set Up Alarm Action
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^^^^^^^^^^^^^^^^^^^
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Most of the use cases of GPTimer should set up the alarm action before starting the timer, except for the simple wall-clock scenario, where a free running timer is enough. To set up the alarm action, one should configure several members of :cpp:type:`gptimer_alarm_config_t` based on how he takes use of the alarm event:
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- :cpp:member:`alarm_count` sets the target count value that will trigger the alarm event. You should also take the counting direction into consideration when setting the alarm value.
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Specially, :cpp:member:`alarm_count` and :cpp:member:`reload_count` can't be set to the same value when :cpp:member:`auto_reload_on_alarm` is true, as keeping reload with a target alarm count is meaningless.
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- :cpp:member:`reload_count` sets the count value to be reloaded when the alarm event happens. This configuration only takes effect when :cpp:member:`auto_reload_on_alarm` is set to true.
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- :cpp:member:`auto_reload_on_alarm` flag sets whether to enable the auto-reload feature. If enabled, the hardware timer will reload the value of :cpp:member:`reload_count` into counter immediately when alarm event happens.
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To make the alarm configurations take effect, one should call :cpp:func:`gptimer_set_alarm_action`. Especially, if :cpp:type:`gptimer_alarm_config_t` is set to ``NULL``, the alarm function will be disabled.
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.. note::
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* If an alarm value is set and the timer has already crossed this value, the alarm will be triggered immediately.
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Register Event Callbacks
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^^^^^^^^^^^^^^^^^^^^^^^^
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After the timer starts up, it can generate specific event (e.g. the "Alarm Event") dynamically. If you have some function that should be called when event happens, you should hook your function to the interrupt service routine by calling :cpp:func:`gptimer_register_event_callbacks`. All supported event callbacks are listed in the :cpp:type:`gptimer_event_callbacks_t`:
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- :cpp:member:`on_alarm` sets callback function for alarm event. As this function is called within the ISR context, user must ensure that the function doesn't attempt to block (e.g., by making sure that only FreeRTOS APIs with ``ISR`` suffix are called from within the function). The function prototype is declared in :cpp:type:`gptimer_alarm_cb_t`.
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One can save his own context to :cpp:func:`gptimer_register_event_callbacks` as well, via the parameter ``user_data``. The user data will be directly passed to the callback functions.
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Start and Stop Timer
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^^^^^^^^^^^^^^^^^^^^
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To start a timer means to enable its internal counter, it can only be achieved by calling :cpp:func:`gptimer_start`. The timer can be stopped at any time (even in the interrupt context) by :cpp:func:`gptimer_stop`. One thing should be kept in mind, calling of :cpp:func:`gptimer_start` should have the same times of calling :cpp:func:`gptimer_stop` before you delete the timer, otherwise the driver might be put in an undetermined state. For example, the timer might keep a Power Management lock, which in return increase the power consumption. Also see `Power management <#power-management>`__ section.
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Start Timer As a Wall Clock
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. code:: c
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ESP_ERROR_CHECK(gptimer_start(gptimer));
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// Retrieve timestamp at anytime
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uint64_t count;
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ESP_ERROR_CHECK(gptimer_get_raw_count(gptimer, &count));
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Trigger Period Events
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~~~~~~~~~~~~~~~~~~~~~
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.. code:: c
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typedef struct {
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uint64_t event_count;
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} example_queue_element_t;
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static bool example_timer_on_alarm_cb(gptimer_handle_t timer, const gptimer_alarm_event_data_t *edata, void *user_ctx)
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{
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BaseType_t high_task_awoken = pdFALSE;
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QueueHandle_t queue = (QueueHandle_t)user_ctx;
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// Retrieve count value from event data
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example_queue_element_t ele = {
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.event_count = edata->count_value
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};
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// Optional: send the event data to other task by OS queue
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// Don't introduce complex logics in callbacks.
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// Suggest dealing with event data in the main loop, instead of in this callback.
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xQueueSendFromISR(queue, &ele, &high_task_awoken);
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// return whether we need to yield at the end of ISR
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return high_task_awoken == pdTRUE;
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}
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gptimer_alarm_config_t alarm_config = {
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.reload_count = 0, // counter will reload with 0 on alarm event
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.alarm_count = 1000000, // period = 1s @resolution 1MHz
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.flags.auto_reload_on_alarm = true, // enable auto-reload
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};
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ESP_ERROR_CHECK(gptimer_set_alarm_action(gptimer, &alarm_config));
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gptimer_event_callbacks_t cbs = {
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.on_alarm = example_timer_on_alarm_cb, // register user callback
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};
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ESP_ERROR_CHECK(gptimer_register_event_callbacks(gptimer, &cbs, queue));
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ESP_ERROR_CHECK(gptimer_start(gptimer));
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Trigger One-Shot Event
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~~~~~~~~~~~~~~~~~~~~~~
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.. code:: c
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typedef struct {
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uint64_t event_count;
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} example_queue_element_t;
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static bool example_timer_on_alarm_cb(gptimer_handle_t timer, const gptimer_alarm_event_data_t *edata, void *user_ctx)
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{
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BaseType_t high_task_awoken = pdFALSE;
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QueueHandle_t queue = (QueueHandle_t)user_ctx;
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// Stop timer the sooner the better
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gptimer_stop(timer);
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// Retrieve count value from event data
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example_queue_element_t ele = {
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.event_count = edata->count_value
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};
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// Optional: send the event data to other task by OS queue
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xQueueSendFromISR(queue, &ele, &high_task_awoken);
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// return whether we need to yield at the end of ISR
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return high_task_awoken == pdTRUE;
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}
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gptimer_alarm_config_t alarm_config = {
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.alarm_count = 1 * 1000 * 1000, // alarm target = 1s @resolution 1MHz
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};
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ESP_ERROR_CHECK(gptimer_set_alarm_action(gptimer, &alarm_config));
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gptimer_event_callbacks_t cbs = {
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.on_alarm = example_timer_on_alarm_cb, // register user callback
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};
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ESP_ERROR_CHECK(gptimer_register_event_callbacks(gptimer, &cbs, queue));
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ESP_ERROR_CHECK(gptimer_start(gptimer));
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Dynamic Alarm Update
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~~~~~~~~~~~~~~~~~~~~
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Alarm value can be updated dynamically inside the ISR handler callback, by changing the :cpp:member:`alarm_value` of :cpp:type:`gptimer_alarm_event_data_t`. Then the alarm value will be updated after the callback function returns.
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.. code:: c
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typedef struct {
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uint64_t event_count;
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} example_queue_element_t;
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static bool example_timer_on_alarm_cb(gptimer_handle_t timer, const gptimer_alarm_event_data_t *edata, void *user_ctx)
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{
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BaseType_t high_task_awoken = pdFALSE;
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QueueHandle_t queue = (QueueHandle_t)user_data;
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// Retrieve count value from event data
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example_queue_element_t ele = {
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.event_count = edata->count_value
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};
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// Optional: send the event data to other task by OS queue
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xQueueSendFromISR(queue, &ele, &high_task_awoken);
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// reconfigure alarm value
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gptimer_alarm_config_t alarm_config = {
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.alarm_count = edata->alarm_value + 1000000, // alarm in next 1s
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};
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gptimer_set_alarm_action(timer, &alarm_config);
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// return whether we need to yield at the end of ISR
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return high_task_awoken == pdTRUE;
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}
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gptimer_alarm_config_t alarm_config = {
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.alarm_count = 1000000, // initial alarm target = 1s @resolution 1MHz
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};
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ESP_ERROR_CHECK(gptimer_set_alarm_action(gptimer, &alarm_config));
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gptimer_event_callbacks_t cbs = {
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.on_alarm = example_timer_on_alarm_cb, // register user callback
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};
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ESP_ERROR_CHECK(gptimer_register_event_callbacks(gptimer, &cbs, queue));
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ESP_ERROR_CHECK(gptimer_start(gptimer, &alarm_config));
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Power Management
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^^^^^^^^^^^^^^^^
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When power management is enabled (i.e. ``CONFIG_PM_ENABLE`` is on), the system will adjust the APB frequency before going into light sleep, thus potentially changing the period of a GPTimer's counting step and leading to inaccurate time keeping.
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However, the driver can prevent the system from changing APB frequency by acquiring a power management lock of type :c:member:`ESP_PM_APB_FREQ_MAX`. Whenever the driver creates a GPTimer instance that has selected :c:member:`GPTIMER_CLK_SRC_APB` as its clock source, the driver will guarantee that the power management lock is acquired when the timer is started by :cpp:func:`gptimer_start`. Likewise, the driver releases the lock when :cpp:func:`gptimer_stop` is called for that timer. This requires that the :cpp:func:`gptimer_start` and :cpp:func:`gptimer_stop` should appear in pairs.
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IRAM Safe
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^^^^^^^^^
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By default, the GPTimer interrupt will be deferred when the Cache is disabled for reasons like writing/erasing Flash. Thus the alarm interrupt will not get executed in time, which is not expected in a real-time application.
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There's a Kconfig option :ref:`CONFIG_GPTIMER_ISR_IRAM_SAFE` that will:
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1. Enable the interrupt being serviced even when cache is disabled
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2. Place all functions that used by the ISR into IRAM [2]_
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3. Place driver object into DRAM (in case it's linked to PSRAM by accident)
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This will allow the interrupt to run while the cache is disabled but will come at the cost of increased IRAM consumption.
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There's another Kconfig option :ref:`CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM` that can put commonly used IO control functions into IRAM as well. So that these functions can also be executable when the cache is disabled. These IO control functions are as follows:
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- :cpp:func:`gptimer_start`
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- :cpp:func:`gptimer_stop`
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- :cpp:func:`gptimer_get_raw_count`
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- :cpp:func:`gptimer_set_raw_count`
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- :cpp:func:`gptimer_set_alarm_action`
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Application Examples
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--------------------
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Typical use cases of GPTimer are listed in the example: :example:`peripherals/timer_group/gptimer`.
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API Reference
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-------------
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.. include-build-file:: inc/gptimer.inc
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.. include-build-file:: inc/timer_types.inc
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.. [1]
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Some ESP chip might only support a sub-set of the clocks, if an unsupported clock source is specified, you will get a runtime error during timer installation.
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.. [2]
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:cpp:member:`on_alarm` callback and the functions invoked by itself should also be placed in IRAM, users need to take care of them by themselves.
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@@ -8,8 +8,8 @@ Peripherals API
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adc
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:SOC_DAC_SUPPORTED: dac
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timer
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gpio
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gptimer
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:SOC_DEDICATED_GPIO_SUPPORTED: dedic_gpio
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:SOC_HMAC_SUPPORTED: hmac
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:SOC_DIG_SIGN_SUPPORTED: ds
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@@ -224,7 +224,7 @@ Application Example
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MCPWM example are located under: :example:`peripherals/mcpwm`:
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* Control of BLDC (brushless DC) motor with hall sensor feedback - :example:`peripherals/mcpwm/mcpwm_bldc_hall_control`
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* Brushed DC motor control - :example:`peripherals/mcpwm/mcpwm_brushed_dc_control`
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* Brushed DC motor control - :example:`peripherals/mcpwm/mcpwm_bdc_speed_control`
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* Servo motor control - :example:`peripherals/mcpwm/mcpwm_servo_control`
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* HC-SR04 sensor with capture - :example:`peripherals/mcpwm/mcpwm_capture_hc_sr04`
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@@ -1,112 +0,0 @@
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General Purpose Timer
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=====================
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:link_to_translation:`zh_CN:[中文]`
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{IDF_TARGET_TIMER_COUNTER_BIT_WIDTH:default="54", esp32="64", esp32s2="64"}
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{IDF_TARGET_TIMER_GROUPS:default="two", esp8684="one"}
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{IDF_TARGET_TIMERS_PER_GROUP:default="two", esp32c3="one", esp8684="one"}
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{IDF_TARGET_TIMERS_TOTAL:default="four", esp32c3="two", esp8684="one"}
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Introduction
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------------
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The {IDF_TARGET_NAME} chip contains {IDF_TARGET_TIMER_GROUPS} hardware timer group(s). Each group has {IDF_TARGET_TIMERS_PER_GROUP} general-purpose hardware timer(s). They are all {IDF_TARGET_TIMER_COUNTER_BIT_WIDTH}-bit generic timers based on 16-bit pre-scalers and {IDF_TARGET_TIMER_COUNTER_BIT_WIDTH}-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 use interrupt callbacks.
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.. _timer-api-timer-initialization:
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Timer Initialization
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^^^^^^^^^^^^^^^^^^^^
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The {IDF_TARGET_TIMER_GROUPS} {IDF_TARGET_NAME} timer group(s), with {IDF_TARGET_TIMERS_PER_GROUP} timer(s) in each, provide the total of {IDF_TARGET_TIMERS_TOTAL} individual timers for use. An {IDF_TARGET_NAME} 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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.. list::
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:not esp32: - **Clock Source**: Select the clock source, which together with the **Divider** define the resolution of the working timer.
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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 clock source that by default is APB_CLK running at 80 MHz. For more information of APB_CLK frequency, please check *{IDF_TARGET_NAME} Technical Reference Manual* > *Reset and Clock* [`PDF <{IDF_TARGET_TRM_EN_URL}#resclk>`__] chapter for more details.
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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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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`.
|
||||
|
||||
To pause the timer at any time, call :cpp:func:`timer_pause`. To resume it, call :cpp:func:`timer_start`.
|
||||
|
||||
To reconfigure the timer, you can call :cpp:func:`timer_init`. This function is described in Section :ref:`timer-api-timer-initialization`.
|
||||
|
||||
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 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, the following two actions can occur depending on the configuration:
|
||||
|
||||
* 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::
|
||||
|
||||
* 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 the specified alarm value, call :cpp:func:`timer_get_alarm_value`.
|
||||
|
||||
|
||||
.. _timer-api-interrupts:
|
||||
|
||||
Interrupts
|
||||
^^^^^^^^^^
|
||||
|
||||
Registration of an interrupt callback for a specific timer can be done by calling :cpp:func:`timer_isr_callback_add` and passing in the group ID, timer ID, callback handler and user data. The callback handler will be invoked in ISR context, so user shouldn't put any blocking API in the callback function.
|
||||
|
||||
The benefit of using interrupt callback instead of precessing interrupt from scratch is, you don't have to deal with interrupt status check and clean stuffs, they are all addressed before the callback got run in driver's default interrupt handler.
|
||||
|
||||
For more information on how to use interrupts, please see the application example below.
|
||||
|
||||
|
||||
Application Example
|
||||
-------------------
|
||||
|
||||
The {IDF_TARGET_TIMER_COUNTER_BIT_WIDTH}-bit hardware timer example: :example:`peripherals/timer_group`.
|
||||
|
||||
|
||||
API Reference
|
||||
-------------
|
||||
|
||||
.. include-build-file:: inc/timer.inc
|
||||
.. include-build-file:: inc/timer_types.inc
|
||||
Reference in New Issue
Block a user