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.

Functional Overview

Typical steps to configure an operate the timer are described in the following sections:

  • Timer Initialization - what parameters should be set up to get the timer working and what specific functionality is provided depending on the set up.
  • Timer Control - how to read the timer’s value, pause / start the timer, and change how it operates.
  • Alarms - setting and using alarms.
  • Interrupts- how to enable and use interrupts.

Timer Initialization

The two timer groups on-board of the ESP32 are identified using timer_group_t. Individual timers in a group are identified with timer_idx_t. The two groups, each having two timers, provide the total of four individual timers to our disposal.

Before starting the timer, it should be initialized by calling timer_init(). This function should be provided with a structure timer_config_t to define how timer should operate. In particular the following timer’s parameters may be set:

  • Divider: How quickly the timer’s counter is “ticking”. This depends on the setting of 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 counter_dir by selecting one of values from timer_count_dir_t.
  • Counter Enable: If the counter is enabled, then it will start incrementing / decrementing immediately after calling timer_init(). This action is set using counter_en by selecting one of vales from timer_start_t.
  • Alarm Enable: Determined by the setting of alarm_en.
  • Auto Reload: Whether the counter should 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 timer_intr_mode_t.

To get the current values of the timers settings, use function timer_get_config().

Timer Control

Once the timer is configured and enabled, it is already “ticking”. To check it’s current value call timer_get_counter_value() or timer_get_counter_time_sec(). To set the timer to specific starting value call timer_set_counter_value().

The timer may be paused at any time by calling timer_pause(). To start it again call timer_start().

To change how the timer operates you can call once more timer_init() described in section Timer Initialization. Another option is to use dedicated functions to change individual settings:

Alarms

To set an alarm, call function timer_set_alarm_value() and then enable it with timer_set_alarm(). The alarm may be also enabled during the timer initialization stage, when 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:

  • An interrupt will be triggered, if previously configured. See section Interrupts how to configure interrupts.
  • When 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 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.

To check what alarm value has been set up, call timer_get_alarm_value().

Interrupts

Registration of the interrupt handler for a specific timer group and timer is done be calling timer_isr_register().

To enable interrupts for a timer group call timer_group_intr_enable(). To do it for a specific timer, call timer_enable_intr(). Disabling of interrupts is done with corresponding functions timer_group_intr_disable() and 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 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:

TIMERG0.int_clr_timers.t1 = 1

See the application example below how to use interrupts.

Application Example

The 64-bit hardware timer example: peripherals/timer_group.

API Reference

Functions

esp_err_t timer_get_counter_value(timer_group_t group_num, timer_idx_t timer_num, uint64_t *timer_val)

Read the counter value of hardware timer.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • timer_val: Pointer to accept timer counter value.

esp_err_t timer_get_counter_time_sec(timer_group_t group_num, timer_idx_t timer_num, double *time)

Read the counter value of hardware timer, in unit of a given scale.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • time: Pointer, type of double*, to accept timer counter value, in seconds.

esp_err_t timer_set_counter_value(timer_group_t group_num, timer_idx_t timer_num, uint64_t load_val)

Set counter value to hardware timer.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • load_val: Counter value to write to the hardware timer.

esp_err_t timer_start(timer_group_t group_num, timer_idx_t timer_num)

Start the counter of hardware timer.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]

esp_err_t timer_pause(timer_group_t group_num, timer_idx_t timer_num)

Pause the counter of hardware timer.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]

esp_err_t timer_set_counter_mode(timer_group_t group_num, timer_idx_t timer_num, timer_count_dir_t counter_dir)

Set counting mode for hardware timer.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • counter_dir: Counting direction of timer, count-up or count-down

esp_err_t timer_set_auto_reload(timer_group_t group_num, timer_idx_t timer_num, timer_autoreload_t reload)

Enable or disable counter reload function when alarm event occurs.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • reload: Counter reload mode.

esp_err_t timer_set_divider(timer_group_t group_num, timer_idx_t timer_num, uint32_t divider)

Set hardware timer source clock divider. Timer groups clock are divider from APB clock.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • divider: Timer clock divider value. The divider’s range is from from 2 to 65536.

esp_err_t timer_set_alarm_value(timer_group_t group_num, timer_idx_t timer_num, uint64_t alarm_value)

Set timer alarm value.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • alarm_value: A 64-bit value to set the alarm value.

esp_err_t timer_get_alarm_value(timer_group_t group_num, timer_idx_t timer_num, uint64_t *alarm_value)

Get timer alarm value.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • alarm_value: Pointer of A 64-bit value to accept the alarm value.

esp_err_t timer_set_alarm(timer_group_t group_num, timer_idx_t timer_num, timer_alarm_t alarm_en)

Enable or disable generation of timer alarm events.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • alarm_en: To enable or disable timer alarm function.

esp_err_t timer_isr_register(timer_group_t group_num, timer_idx_t timer_num, void (*fn)(void *), void *arg, int intr_alloc_flags, timer_isr_handle_t *handle, )

Register Timer interrupt handler, the handler is an ISR. The handler will be attached to the same CPU core that this function is running on.

Note
If the intr_alloc_flags value ESP_INTR_FLAG_IRAM is set, the handler function must be declared with IRAM_ATTR attribute and can only call functions in IRAM or ROM. It cannot call other timer APIs. Use direct register access to configure timers from inside the ISR in this case.
Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number
  • timer_num: Timer index of timer group
  • fn: Interrupt handler function.
  • arg: Parameter for handler function
  • intr_alloc_flags: Flags used to allocate the interrupt. One or multiple (ORred) ESP_INTR_FLAG_* values. See esp_intr_alloc.h for more info.
  • handle: Pointer to return handle. If non-NULL, a handle for the interrupt will be returned here.

esp_err_t timer_init(timer_group_t group_num, timer_idx_t timer_num, const timer_config_t *config)

Initializes and configure the timer.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • config: Pointer to timer initialization parameters.

esp_err_t timer_get_config(timer_group_t group_num, timer_idx_t timer_num, timer_config_t *config)

Get timer configure value.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index, 0 for hw_timer[0] & 1 for hw_timer[1]
  • config: Pointer of struct to accept timer parameters.

esp_err_t timer_group_intr_enable(timer_group_t group_num, uint32_t en_mask)

Enable timer group interrupt, by enable mask.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • en_mask: Timer interrupt enable mask. Use TIMG_T0_INT_ENA_M to enable t0 interrupt Use TIMG_T1_INT_ENA_M to enable t1 interrupt

esp_err_t timer_group_intr_disable(timer_group_t group_num, uint32_t disable_mask)

Disable timer group interrupt, by disable mask.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • disable_mask: Timer interrupt disable mask. Use TIMG_T0_INT_ENA_M to disable t0 interrupt Use TIMG_T1_INT_ENA_M to disable t1 interrupt

esp_err_t timer_enable_intr(timer_group_t group_num, timer_idx_t timer_num)

Enable timer interrupt.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index.

esp_err_t timer_disable_intr(timer_group_t group_num, timer_idx_t timer_num)

Disable timer interrupt.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • group_num: Timer group number, 0 for TIMERG0 or 1 for TIMERG1
  • timer_num: Timer index.

Structures

struct timer_config_t

Data structure with timer’s configuration settings.

Public Members

bool alarm_en

Timer alarm enable

bool counter_en

Counter enable

timer_intr_mode_t intr_type

Interrupt mode

timer_count_dir_t counter_dir

Counter direction

bool auto_reload

Timer auto-reload

uint32_t divider

Counter clock divider. The divider’s range is from from 2 to 65536.

Macros

TIMER_BASE_CLK

Frequency of the clock on the input of the timer groups

Type Definitions

typedef intr_handle_t timer_isr_handle_t

Interrupt handle, used in order to free the isr after use. Aliases to an int handle for now.

Enumerations

enum timer_group_t

Selects a Timer-Group out of 2 available groups.

Values:

TIMER_GROUP_0 = 0

Hw timer group 0

TIMER_GROUP_1 = 1

Hw timer group 1

TIMER_GROUP_MAX
enum timer_idx_t

Select a hardware timer from timer groups.

Values:

TIMER_0 = 0

Select timer0 of GROUPx

TIMER_1 = 1

Select timer1 of GROUPx

TIMER_MAX
enum timer_count_dir_t

Decides the direction of counter.

Values:

TIMER_COUNT_DOWN = 0

Descending Count from cnt.high|cnt.low

TIMER_COUNT_UP = 1

Ascending Count from Zero

TIMER_COUNT_MAX
enum timer_start_t

Decides whether timer is on or paused.

Values:

TIMER_PAUSE = 0

Pause timer counter

TIMER_START = 1

Start timer counter

enum timer_alarm_t

Decides whether to enable alarm mode.

Values:

TIMER_ALARM_DIS = 0

Disable timer alarm

TIMER_ALARM_EN = 1

Enable timer alarm

TIMER_ALARM_MAX
enum timer_intr_mode_t

Select interrupt type if running in alarm mode.

Values:

TIMER_INTR_LEVEL = 0

Interrupt mode: level mode

TIMER_INTR_MAX
enum timer_autoreload_t

Select if Alarm needs to be loaded by software or automatically reload by hardware.

Values:

TIMER_AUTORELOAD_DIS = 0

Disable auto-reload: hardware will not load counter value after an alarm event

TIMER_AUTORELOAD_EN = 1

Enable auto-reload: hardware will load counter value after an alarm event

TIMER_AUTORELOAD_MAX