# General Purpose Timer (GPTimer)

## Introduction

GPTimer (General Purpose Timer) is the driver of ESP32 Timer Group peripheral. The hardware timer features high resolution and flexible alarm action. The behavior when the internal counter of a timer reaches a specific target value is called a timer alarm. When a timer alarms, a user registered per-timer callback would be called.

Typically, a general purpose timer can be used in scenarios like:

- Free running as a wall clock, fetching a high-resolution timestamp at any time and any places

- Generate period alarms, trigger events periodically

- Generate one-shot alarm, respond in target time

## Functional Overview

The following sections of this document cover the typical steps to install and operate a timer:

- Resource Allocation - covers which parameters should be set up to get a timer handle and how to recycle the resources when GPTimer finishes working.

- 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.

- Set up Alarm Action - covers the parameters that should be set up to enable the alarm event.

- Register Event Callbacks - covers how to hook user specific code to the alarm event callback function.

- Enable and Disable Timer - covers how to enable and disable the timer.

- Start and Stop Timer - shows some typical use cases that start the timer with different alarm behavior.

- Power Management - describes how different source clock selections can affect power consumption.

- IRAM Safe - describes tips on how to make the timer interrupt and IO control functions work better along with a disabled cache.

- Thread Safety - lists which APIs are guaranteed to be thread safe by the driver.

- Kconfig Options - lists the supported Kconfig options that can be used to make a different effect on driver behavior.

### Resource Allocation

Different ESP chips might have different numbers of independent timer groups, and within each group, there could also be several independent timers. [1]

A GPTimer instance is represented by `gptimer_handle_t`. The driver behind manages all available hardware resources in a pool, so that you do not need to care about which timer and which group it belongs to.

To install a timer instance, there is a configuration structure that needs to be given in advance: `gptimer_config_t`:

- `gptimer_config_t::clk_src` selects the source clock for the timer. The available clocks are listed in `gptimer_clock_source_t`, you can only pick one of them. For the effect on power consumption of different clock source, please refer to Section Power Management.

- `gptimer_config_t::direction` sets the counting direction of the timer, supported directions are listed in `gptimer_count_direction_t`, you can only pick one of them.

- `gptimer_config_t::resolution_hz` sets the resolution of the internal counter. Each count step is equivalent to 1 / resolution_hz seconds.

- `gptimer_config::intr_priority` sets the priority of the timer interrupt. If it is set to `0`, the driver will allocate an interrupt with a default priority. Otherwise, the driver will use the given priority.

- `gptimer_config_t::backup_before_sleep` enables the backup of the GPTimer registers before entering sleep mode. This option implies an balance between power consumption and memory usage. If the power consumption is not a concern, you can disable this option to save memory. But if you want to save more power, you should enable this option to backup the GPTimer registers before entering sleep mode, and restore them after waking up. This feature depends on specific hardware module, if you enable this flag on an unsupported chip, you will get an error message like `register back up is not supported`.

- Optional `gptimer_config_t::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 Interrupt Handling.

With all the above configurations set in the structure, the structure can be passed to `gptimer_new_timer()` which will instantiate the timer instance and return a handle of the timer.

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 `ESP_ERR_NOT_FOUND` will be returned. The total number of available timers is represented by the `SOC_TIMER_GROUP_TOTAL_TIMERS` and its value depends on the ESP chip.

If a previously created GPTimer instance is no longer required, you should recycle the timer by calling `gptimer_del_timer()`. This allows the underlying HW timer to be used for other purposes. Before deleting a GPTimer handle, please disable it by `gptimer_disable()` in advance or make sure it has not enabled yet by `gptimer_enable()`.

#### Creating a GPTimer Handle with Resolution of 1 MHz

    gptimer_handle_t gptimer = NULL;
    gptimer_config_t timer_config = {
        .clk_src = GPTIMER_CLK_SRC_DEFAULT,
        .direction = GPTIMER_COUNT_UP,
        .resolution_hz = 1 * 1000 * 1000, // 1MHz, 1 tick = 1us
    };
    ESP_ERROR_CHECK(gptimer_new_timer(&timer_config, &gptimer));

### Set and Get Count Value

When the GPTimer is created, the internal counter will be reset to zero by default. The counter value can be updated asynchronously by `gptimer_set_raw_count()`. The maximum count value is dependent on the bit width of the hardware timer, which is also reflected by the SOC 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.

Count value can be retrieved by `gptimer_get_raw_count()`, at any time.

### Set up Alarm Action

For most of the use cases of GPTimer, you 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, you should configure several members of `gptimer_alarm_config_t` based on how you make use of the alarm event:

- `gptimer_alarm_config_t::alarm_count` sets the target count value that triggers the alarm event. You should also take the counting direction into consideration when setting the alarm value. Specially, `gptimer_alarm_config_t::alarm_count` and `gptimer_alarm_config_t::reload_count` cannot be set to the same value when `gptimer_alarm_config_t::auto_reload_on_alarm` is true, as keeping reload with a target alarm count is meaningless. Please also note, because of the interrupt latency, it's not recommended to set the alarm period smaller than 5 us.

- `gptimer_alarm_config_t::reload_count` sets the count value to be reloaded when the alarm event happens. This configuration only takes effect when `gptimer_alarm_config_t::auto_reload_on_alarm` is set to true.

- `gptimer_alarm_config_t::auto_reload_on_alarm` flag sets whether to enable the auto-reload feature. If enabled, the hardware timer will reload the value of `gptimer_alarm_config_t::reload_count` into counter immediately when an alarm event happens.

To make the alarm configurations take effect, you should call `gptimer_set_alarm_action()`. Especially, if `gptimer_alarm_config_t` is set to `NULL`, the alarm function will be disabled.

Note

If an alarm value is set and the timer has already exceeded this value, the alarm will be triggered immediately.

### Register Event Callbacks

After the timer starts up, it can generate a specific event (e.g., the "Alarm Event") dynamically. If you have some functions that should be called when the event happens, please hook your function to the interrupt service routine by calling `gptimer_register_event_callbacks()`. All supported event callbacks are listed in `gptimer_event_callbacks_t`:

- `gptimer_event_callbacks_t::on_alarm` sets a callback function for alarm events. As this function is called within the ISR context, you must ensure that the function does not 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 `gptimer_alarm_cb_t`.

You can save your own context to `gptimer_register_event_callbacks()` as well, via the parameter `user_data`. The user data will be directly passed to the callback function.

This function lazy installs the interrupt service for the timer but not enable it. So please call this function before `gptimer_enable()`, otherwise the `ESP_ERR_INVALID_STATE` error will be returned. See Section Enable and Disable Timer for more information.

### Enable and Disable Timer

Before doing IO control to the timer, you needs to enable the timer first, by calling `gptimer_enable()`. This function:

- Switches the timer driver state from init to enable.

- Enables the interrupt service if it has been lazy installed by `gptimer_register_event_callbacks()`.

- Acquires a proper power management lock if a specific clock source (e.g., APB clock) is selected. See Section Power Management for more information.

Calling `gptimer_disable()` does the opposite, that is, put the timer driver back to the init state, disable the interrupts service and release the power management lock.

### Start and Stop Timer

The basic IO operation of a timer is to start and stop. Calling `gptimer_start()` can make the internal counter work, while calling `gptimer_stop()` can make the counter stop working. The following illustrates how to start a timer with or without an alarm event.

Calling `gptimer_start()` transits the driver state from enable to run, and vice versa. You need to make sure the start and stop functions are used in pairs, otherwise, the functions may return `ESP_ERR_INVALID_STATE`. Most of the time, this error means that the timer is already stopped or in the "start protection" state (i.e., `gptimer_start()` is called but not finished).

#### Start Timer as a Wall Clock

    ESP_ERROR_CHECK(gptimer_enable(gptimer));
    ESP_ERROR_CHECK(gptimer_start(gptimer));
    // Retrieve the timestamp at any time
    uint64_t count;
    ESP_ERROR_CHECK(gptimer_get_raw_count(gptimer, &count));

#### Trigger Period Events

    typedef struct {
        uint64_t event_count;
    } example_queue_element_t;

    static bool example_timer_on_alarm_cb(gptimer_handle_t timer, const gptimer_alarm_event_data_t *edata, void *user_ctx)
    {
        BaseType_t high_task_awoken = pdFALSE;
        QueueHandle_t queue = (QueueHandle_t)user_ctx;
        // Retrieve the count value from event data
        example_queue_element_t ele = {
            .event_count = edata->count_value
        };
        // Optional: send the event data to other task by OS queue
        // Do not introduce complex logics in callbacks
        // Suggest dealing with event data in the main loop, instead of in this callback
        xQueueSendFromISR(queue, &ele, &high_task_awoken);
        // return whether we need to yield at the end of ISR
        return high_task_awoken == pdTRUE;
    }

    gptimer_alarm_config_t alarm_config = {
        .reload_count = 0, // counter will reload with 0 on alarm event
        .alarm_count = 1000000, // period = 1s @resolution 1MHz
        .flags.auto_reload_on_alarm = true, // enable auto-reload
    };
    ESP_ERROR_CHECK(gptimer_set_alarm_action(gptimer, &alarm_config));

    gptimer_event_callbacks_t cbs = {
        .on_alarm = example_timer_on_alarm_cb, // register user callback
    };
    ESP_ERROR_CHECK(gptimer_register_event_callbacks(gptimer, &cbs, queue));
    ESP_ERROR_CHECK(gptimer_enable(gptimer));
    ESP_ERROR_CHECK(gptimer_start(gptimer));

#### Trigger One-Shot Event

    typedef struct {
        uint64_t event_count;
    } example_queue_element_t;

    static bool example_timer_on_alarm_cb(gptimer_handle_t timer, const gptimer_alarm_event_data_t *edata, void *user_ctx)
    {
        BaseType_t high_task_awoken = pdFALSE;
        QueueHandle_t queue = (QueueHandle_t)user_ctx;
        // Stop timer the sooner the better
        gptimer_stop(timer);
        // Retrieve the count value from event data
        example_queue_element_t ele = {
            .event_count = edata->count_value
        };
        // Optional: send the event data to other task by OS queue
        xQueueSendFromISR(queue, &ele, &high_task_awoken);
        // return whether we need to yield at the end of ISR
        return high_task_awoken == pdTRUE;
    }

    gptimer_alarm_config_t alarm_config = {
        .alarm_count = 1 * 1000 * 1000, // alarm target = 1s @resolution 1MHz
    };
    ESP_ERROR_CHECK(gptimer_set_alarm_action(gptimer, &alarm_config));

    gptimer_event_callbacks_t cbs = {
        .on_alarm = example_timer_on_alarm_cb, // register user callback
    };
    ESP_ERROR_CHECK(gptimer_register_event_callbacks(gptimer, &cbs, queue));
    ESP_ERROR_CHECK(gptimer_enable(gptimer));
    ESP_ERROR_CHECK(gptimer_start(gptimer));

#### Dynamic Alarm Update

Alarm value can be updated dynamically inside the ISR handler callback, by changing `gptimer_alarm_event_data_t::alarm_value`. Then the alarm value will be updated after the callback function returns.

    typedef struct {
        uint64_t event_count;
    } example_queue_element_t;

    static bool example_timer_on_alarm_cb(gptimer_handle_t timer, const gptimer_alarm_event_data_t *edata, void *user_ctx)
    {
        BaseType_t high_task_awoken = pdFALSE;
        QueueHandle_t queue = (QueueHandle_t)user_data;
        // Retrieve the count value from event data
        example_queue_element_t ele = {
            .event_count = edata->count_value
        };
        // Optional: send the event data to other task by OS queue
        xQueueSendFromISR(queue, &ele, &high_task_awoken);
        // reconfigure alarm value
        gptimer_alarm_config_t alarm_config = {
            .alarm_count = edata->alarm_value + 1000000, // alarm in next 1s
        };
        gptimer_set_alarm_action(timer, &alarm_config);
        // return whether we need to yield at the end of ISR
        return high_task_awoken == pdTRUE;
    }

    gptimer_alarm_config_t alarm_config = {
        .alarm_count = 1000000, // initial alarm target = 1s @resolution 1MHz
    };
    ESP_ERROR_CHECK(gptimer_set_alarm_action(gptimer, &alarm_config));

    gptimer_event_callbacks_t cbs = {
        .on_alarm = example_timer_on_alarm_cb, // register user callback
    };
    ESP_ERROR_CHECK(gptimer_register_event_callbacks(gptimer, &cbs, queue));
    ESP_ERROR_CHECK(gptimer_enable(gptimer));
    ESP_ERROR_CHECK(gptimer_start(gptimer));

### Power Management

When power management is enabled, i.e., CONFIG_PM_ENABLE is on, the system may adjust or disable the clock source before going to sleep. As a result, the time keeping will be inaccurate.

The driver can prevent the above issue by creating a power management lock. The lock type is set based on different clock sources. The driver will acquire the lock in `gptimer_enable()`, and release it in `gptimer_disable()`. So that the timer can work correctly in between these two functions, because the clock source won't be disabled or adjusted its frequency during this time.

### IRAM Safe

By default, the GPTimer interrupt will be deferred when the cache is disabled because of writing or erasing the flash. Thus the alarm interrupt will not get executed in time, which is not expected in a real-time application.

There is a Kconfig option CONFIG_GPTIMER_ISR_IRAM_SAFE that:

- Enables the interrupt being serviced even when the cache is disabled

- Places all functions that used by the ISR into IRAM [2]

- Places driver object into DRAM (in case it is mapped to PSRAM by accident)

This allows the interrupt to run while the cache is disabled, but comes at the cost of increased IRAM consumption.

There is another Kconfig option CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM that can put commonly used IO control functions into IRAM as well. So, these functions can also be executable when the cache is disabled. These IO control functions are as follows:

- `gptimer_start()`

- `gptimer_stop()`

- `gptimer_get_raw_count()`

- `gptimer_set_raw_count()`

- `gptimer_set_alarm_action()`

### Thread Safety

All the APIs provided by the driver are guaranteed to be thread safe, which means you can call them from different RTOS tasks without protection by extra locks. The following functions are allowed to run under ISR context.

- `gptimer_start()`

- `gptimer_stop()`

- `gptimer_get_raw_count()`

- `gptimer_set_raw_count()`

- `gptimer_get_captured_count()`

- `gptimer_set_alarm_action()`

### Kconfig Options

- CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM controls where to place the GPTimer control functions (IRAM or flash).

- CONFIG_GPTIMER_ISR_HANDLER_IN_IRAM controls where to place the GPTimer ISR handler (IRAM or flash).

- CONFIG_GPTIMER_ISR_IRAM_SAFE controls whether the default ISR handler should be masked when the cache is disabled, see Section IRAM Safe for more information.

- CONFIG_GPTIMER_ENABLE_DEBUG_LOG is used to enabled the debug log output. Enable this option will increase the firmware binary size.

## Application Examples

- Typical use cases of GPTimer are listed in the example peripherals/timer_group/gptimer.

## API Reference

### Header File

- components/esp_driver_gptimer/include/driver/gptimer.h

- This header file can be included with:

  >     #include "driver/gptimer.h"

- This header file is a part of the API provided by the `esp_driver_gptimer` component. To declare that your component depends on `esp_driver_gptimer`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_driver_gptimer

  > or

  >     PRIV_REQUIRES esp_driver_gptimer

### Functions

esp_err_t gptimer_new_timer(const gptimer_config_t *config, gptimer_handle_t *ret_timer)

  Create a new General Purpose Timer, and return the handle.

  Note

  The newly created timer is put in the "init" state.

  Parameters:

    - config -- [in] GPTimer configuration

    - ret_timer -- [out] Returned timer handle

  Returns:

    - ESP_OK: Create GPTimer successfully

    - ESP_ERR_INVALID_ARG: Create GPTimer failed because of invalid argument

    - ESP_ERR_NO_MEM: Create GPTimer failed because out of memory

    - ESP_ERR_NOT_FOUND: Create GPTimer failed because all hardware timers are used up and no more free one

    - ESP_FAIL: Create GPTimer failed because of other error

esp_err_t gptimer_del_timer(gptimer_handle_t timer)

  Delete the GPTimer handle.

  Note

  A timer must be in the "init" state before it can be deleted.

  Parameters:

    timer -- [in] Timer handle created by `gptimer_new_timer`

  Returns:

    - ESP_OK: Delete GPTimer successfully

    - ESP_ERR_INVALID_ARG: Delete GPTimer failed because of invalid argument

    - ESP_ERR_INVALID_STATE: Delete GPTimer failed because the timer is not in init state

    - ESP_FAIL: Delete GPTimer failed because of other error

esp_err_t gptimer_set_raw_count(gptimer_handle_t timer, uint64_t value)

  Set GPTimer raw count value.

  Note

  When updating the raw count of an active timer, the timer will immediately start counting from the new value.

  Note

  This function is allowed to run within ISR context

  Note

  If `CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM` is enabled, this function will be placed in the IRAM by linker, makes it possible to execute even when the Flash Cache is disabled.

  Parameters:

    - timer -- [in] Timer handle created by `gptimer_new_timer`

    - value -- [in] Count value to be set

  Returns:

    - ESP_OK: Set GPTimer raw count value successfully

    - ESP_ERR_INVALID_ARG: Set GPTimer raw count value failed because of invalid argument

    - ESP_FAIL: Set GPTimer raw count value failed because of other error

esp_err_t gptimer_get_raw_count(gptimer_handle_t timer, uint64_t *value)

  Get GPTimer raw count value.

  Note

  This function will trigger a software capture event and then return the captured count value.

  Note

  With the raw count value and the resolution returned from `gptimer_get_resolution`, you can convert the count value into seconds.

  Note

  This function is allowed to run within ISR context

  Note

  If `CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM` is enabled, this function will be placed in the IRAM by linker, makes it possible to execute even when the Flash Cache is disabled.

  Parameters:

    - timer -- [in] Timer handle created by `gptimer_new_timer`

    - value -- [out] Returned GPTimer count value

  Returns:

    - ESP_OK: Get GPTimer raw count value successfully

    - ESP_ERR_INVALID_ARG: Get GPTimer raw count value failed because of invalid argument

    - ESP_FAIL: Get GPTimer raw count value failed because of other error

esp_err_t gptimer_get_resolution(gptimer_handle_t timer, uint32_t *out_resolution)

  Return the real resolution of the timer.

  Note

  usually the timer resolution is same as what you configured in the `gptimer_config_t::resolution_hz`, but some unstable clock source (e.g. RC_FAST) will do a calibration, the real resolution can be different from the configured one.

  Parameters:

    - timer -- [in] Timer handle created by `gptimer_new_timer`

    - out_resolution -- [out] Returned timer resolution, in Hz

  Returns:

    - ESP_OK: Get GPTimer resolution successfully

    - ESP_ERR_INVALID_ARG: Get GPTimer resolution failed because of invalid argument

    - ESP_FAIL: Get GPTimer resolution failed because of other error

esp_err_t gptimer_get_captured_count(gptimer_handle_t timer, uint64_t *value)

  Get GPTimer captured count value.

  Note

  The capture action can be issued either by ETM event or by software (see also `gptimer_get_raw_count`).

  Note

  This function is allowed to run within ISR context

  Note

  If `CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM` is enabled, this function will be placed in the IRAM by linker, makes it possible to execute even when the Flash Cache is disabled.

  Parameters:

    - timer -- [in] Timer handle created by `gptimer_new_timer`

    - value -- [out] Returned captured count value

  Returns:

    - ESP_OK: Get GPTimer captured count value successfully

    - ESP_ERR_INVALID_ARG: Get GPTimer captured count value failed because of invalid argument

    - ESP_FAIL: Get GPTimer captured count value failed because of other error

esp_err_t gptimer_register_event_callbacks(gptimer_handle_t timer, const gptimer_event_callbacks_t *cbs, void *user_data)

  Set callbacks for GPTimer.

  Note

  User registered callbacks are expected to be runnable within ISR context

  Note

  The first call to this function needs to be before the call to `gptimer_enable`

  Note

  User can deregister a previously registered callback by calling this function and setting the callback member in the `cbs` structure to NULL.

  Parameters:

    - timer -- [in] Timer handle created by `gptimer_new_timer`

    - cbs -- [in] Group of callback functions

    - user_data -- [in] User data, which will be passed to callback functions directly

  Returns:

    - ESP_OK: Set event callbacks successfully

    - ESP_ERR_INVALID_ARG: Set event callbacks failed because of invalid argument

    - ESP_ERR_INVALID_STATE: Set event callbacks failed because the timer is not in init state

    - ESP_FAIL: Set event callbacks failed because of other error

esp_err_t gptimer_set_alarm_action(gptimer_handle_t timer, const gptimer_alarm_config_t *config)

  Set alarm event actions for GPTimer.

  Note

  This function is allowed to run within ISR context, so you can update new alarm action immediately in any ISR callback.

  Note

  If `CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM` is enabled, this function will be placed in the IRAM by linker, makes it possible to execute even when the Flash Cache is disabled. In this case, please also ensure the `gptimer_alarm_config_t` instance is placed in the static data section instead of in the read-only data section. e.g.: `static gptimer_alarm_config_t alarm_config = { ... };`

  Parameters:

    - timer -- [in] Timer handle created by `gptimer_new_timer`

    - config -- [in] Alarm configuration, especially, set config to NULL means disabling the alarm function

  Returns:

    - ESP_OK: Set alarm action for GPTimer successfully

    - ESP_ERR_INVALID_ARG: Set alarm action for GPTimer failed because of invalid argument

    - ESP_FAIL: Set alarm action for GPTimer failed because of other error

esp_err_t gptimer_enable(gptimer_handle_t timer)

  Enable GPTimer.

  Note

  This function will transit the timer state from "init" to "enable".

  Note

  This function will enable the interrupt service, if it's lazy installed in `gptimer_register_event_callbacks`.

  Note

  This function will acquire a PM lock, if a specific source clock (e.g. APB) is selected in the `gptimer_config_t`, while `CONFIG_PM_ENABLE` is enabled.

  Note

  Enable a timer doesn't mean to start it. See also `gptimer_start` for how to make the timer start counting.

  Parameters:

    timer -- [in] Timer handle created by `gptimer_new_timer`

  Returns:

    - ESP_OK: Enable GPTimer successfully

    - ESP_ERR_INVALID_ARG: Enable GPTimer failed because of invalid argument

    - ESP_ERR_INVALID_STATE: Enable GPTimer failed because the timer is already enabled

    - ESP_FAIL: Enable GPTimer failed because of other error

esp_err_t gptimer_disable(gptimer_handle_t timer)

  Disable GPTimer.

  Note

  This function will transit the timer state from "enable" to "init".

  Note

  This function will disable the interrupt service if it's installed.

  Note

  This function will release the PM lock if it's acquired in the `gptimer_enable`.

  Note

  Disable a timer doesn't mean to stop it. See also `gptimer_stop` for how to make the timer stop counting.

  Parameters:

    timer -- [in] Timer handle created by `gptimer_new_timer`

  Returns:

    - ESP_OK: Disable GPTimer successfully

    - ESP_ERR_INVALID_ARG: Disable GPTimer failed because of invalid argument

    - ESP_ERR_INVALID_STATE: Disable GPTimer failed because the timer is not enabled yet

    - ESP_FAIL: Disable GPTimer failed because of other error

esp_err_t gptimer_start(gptimer_handle_t timer)

  Start GPTimer (internal counter starts counting)

  Note

  This function will transit the timer state from "enable" to "run".

  Note

  This function is allowed to run within ISR context

  Note

  If `CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM` is enabled, this function will be placed in the IRAM by linker, makes it possible to execute even when the Flash Cache is disabled.

  Parameters:

    timer -- [in] Timer handle created by `gptimer_new_timer`

  Returns:

    - ESP_OK: Start GPTimer successfully

    - ESP_ERR_INVALID_ARG: Start GPTimer failed because of invalid argument

    - ESP_ERR_INVALID_STATE: Start GPTimer failed because the timer is not enabled or is already in running

    - ESP_FAIL: Start GPTimer failed because of other error

esp_err_t gptimer_stop(gptimer_handle_t timer)

  Stop GPTimer (internal counter stops counting)

  Note

  This function will transit the timer state from "run" to "enable".

  Note

  This function is allowed to run within ISR context

  Note

  If `CONFIG_GPTIMER_CTRL_FUNC_IN_IRAM` is enabled, this function will be placed in the IRAM by linker, makes it possible to execute even when the Flash Cache is disabled.

  Parameters:

    timer -- [in] Timer handle created by `gptimer_new_timer`

  Returns:

    - ESP_OK: Stop GPTimer successfully

    - ESP_ERR_INVALID_ARG: Stop GPTimer failed because of invalid argument

    - ESP_ERR_INVALID_STATE: Stop GPTimer failed because the timer is not in running.

    - ESP_FAIL: Stop GPTimer failed because of other error

### Structures

struct gptimer_config_t

  General Purpose Timer configuration.

  Public Members

  gptimer_clock_source_t clk_src

    GPTimer clock source

  gptimer_count_direction_t direction

    Count direction

  uint32_t resolution_hz

    Counter resolution (working frequency) in Hz, hence, the step size of each count tick equals to (1 / resolution_hz) seconds

  int intr_priority

    GPTimer interrupt priority, if set to 0, the driver will try to allocate an interrupt with a relative low priority (1,2,3)

  uint32_t intr_shared

    Set true, the timer interrupt number can be shared with other peripherals

  uint32_t backup_before_sleep

    If set, the driver will backup/restore the GPTimer registers before/after entering/exist sleep mode. By this approach, the system can power off GPTimer's power domain. This can save power, but at the expense of more RAM being consumed

  struct gptimer_config_t::[anonymous] flags

    GPTimer config flags

struct gptimer_event_callbacks_t

  Group of supported GPTimer callbacks.

  Note

  The callbacks are all running under ISR environment

  Note

  When CONFIG_GPTIMER_ISR_IRAM_SAFE is enabled, the callback itself and functions called by it should be placed in IRAM.

  Public Members

  gptimer_alarm_cb_t on_alarm

    Timer alarm callback

struct gptimer_alarm_config_t

  General Purpose Timer alarm configuration.

  Public Members

  uint64_t alarm_count

    Alarm target count value

  uint64_t reload_count

    Alarm reload count value, effect only when `auto_reload_on_alarm` is set to true

  uint32_t auto_reload_on_alarm

    Reload the count value by hardware, immediately at the alarm event

  struct gptimer_alarm_config_t::[anonymous] flags

    Alarm config flags

### Header File

- components/esp_driver_gptimer/include/driver/gptimer_etm.h

- This header file can be included with:

  >     #include "driver/gptimer_etm.h"

- This header file is a part of the API provided by the `esp_driver_gptimer` component. To declare that your component depends on `esp_driver_gptimer`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_driver_gptimer

  > or

  >     PRIV_REQUIRES esp_driver_gptimer

### Functions

esp_err_t gptimer_new_etm_event(gptimer_handle_t timer, const gptimer_etm_event_config_t *config, esp_etm_event_handle_t *out_event)

  Get the ETM event for GPTimer.

  Note

  The created ETM event object can be deleted later by calling `esp_etm_del_event`

  Parameters:

    - timer -- [in] Timer handle created by `gptimer_new_timer`

    - config -- [in] GPTimer ETM event configuration

    - out_event -- [out] Returned ETM event handle

  Returns:

    - ESP_OK: Get ETM event successfully

    - ESP_ERR_INVALID_ARG: Get ETM event failed because of invalid argument

    - ESP_FAIL: Get ETM event failed because of other error

esp_err_t gptimer_new_etm_task(gptimer_handle_t timer, const gptimer_etm_task_config_t *config, esp_etm_task_handle_t *out_task)

  Get the ETM task for GPTimer.

  Note

  The created ETM task object can be deleted later by calling `esp_etm_del_task`

  Parameters:

    - timer -- [in] Timer handle created by `gptimer_new_timer`

    - config -- [in] GPTimer ETM task configuration

    - out_task -- [out] Returned ETM task handle

  Returns:

    - ESP_OK: Get ETM task successfully

    - ESP_ERR_INVALID_ARG: Get ETM task failed because of invalid argument

    - ESP_FAIL: Get ETM task failed because of other error

### Structures

struct gptimer_etm_event_config_t

  GPTimer ETM event configuration.

  Public Members

  gptimer_etm_event_type_t event_type

    GPTimer ETM event type

struct gptimer_etm_task_config_t

  GPTimer ETM task configuration.

  Public Members

  gptimer_etm_task_type_t task_type

    GPTimer ETM task type

### Header File

- components/esp_driver_gptimer/include/driver/gptimer_types.h

- This header file can be included with:

  >     #include "driver/gptimer_types.h"

- This header file is a part of the API provided by the `esp_driver_gptimer` component. To declare that your component depends on `esp_driver_gptimer`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_driver_gptimer

  > or

  >     PRIV_REQUIRES esp_driver_gptimer

### Structures

struct gptimer_alarm_event_data_t

  GPTimer alarm event data.

  Public Members

  uint64_t count_value

    Current count value

  uint64_t alarm_value

    Current alarm value

### Type Definitions

typedef struct gptimer_t *gptimer_handle_t

  Type of General Purpose Timer handle.

typedef bool (*gptimer_alarm_cb_t)(gptimer_handle_t timer, const gptimer_alarm_event_data_t *edata, void *user_ctx)

  Timer alarm callback prototype.

  Param timer:

    [in] Timer handle created by `gptimer_new_timer`

  Param edata:

    [in] Alarm event data, fed by driver

  Param user_ctx:

    [in] User data, passed from `gptimer_register_event_callbacks`

  Return:

    Whether a high priority task has been waken up by this function

### Header File

- components/hal/include/hal/timer_types.h

- This header file can be included with:

  >     #include "hal/timer_types.h"

### Type Definitions

typedef soc_periph_gptimer_clk_src_t gptimer_clock_source_t

  GPTimer clock source.

  Note

  User should select the clock source based on the power and resolution requirement

### Enumerations

enum gptimer_count_direction_t

  GPTimer count direction.

  Values:

  enumerator GPTIMER_COUNT_DOWN

    Decrease count value

  enumerator GPTIMER_COUNT_UP

    Increase count value

enum gptimer_etm_task_type_t

  GPTimer specific tasks that supported by the ETM module.

  Values:

  enumerator GPTIMER_ETM_TASK_START_COUNT

    Start the counter

  enumerator GPTIMER_ETM_TASK_STOP_COUNT

    Stop the counter

  enumerator GPTIMER_ETM_TASK_EN_ALARM

    Enable the alarm

  enumerator GPTIMER_ETM_TASK_RELOAD

    Reload preset value into counter

  enumerator GPTIMER_ETM_TASK_CAPTURE

    Capture current count value into specific register

  enumerator GPTIMER_ETM_TASK_MAX

    Maximum number of tasks

enum gptimer_etm_event_type_t

  GPTimer specific events that supported by the ETM module.

  Values:

  enumerator GPTIMER_ETM_EVENT_ALARM_MATCH

    Count value matches the alarm target value

  enumerator GPTIMER_ETM_EVENT_MAX

    Maximum number of events

[1]

Different ESP chip series might have different numbers of GPTimer instances. For more details, please refer to ESP32 Technical Reference Manual > Chapter Timer Group (TIMG) [PDF]. The driver does forbid you from applying for more timers, but it returns error when all available hardware resources are used up. Please always check the return value when doing resource allocation (e.g., `gptimer_new_timer()`).

[2]

`gptimer_event_callbacks_t::on_alarm` callback and the functions invoked by the callback should also be placed in IRAM, please take care of them by yourself.

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