Timers

LVGL has a built-in timer system. You can register a function to have it be called periodically. The timers are handled and called in lv_timer_handler(), which needs to be called every few milliseconds. See Porting for more information.

Timers are non-preemptive, which means a timer cannot interrupt another timer. Therefore, you can call any LVGL related function in a timer.

Create a timer

To create a new timer, use lv_timer_create(timer_cb, period_ms, user_data). It will create an lv_timer_t * variable, which can be used later to modify the parameters of the timer. lv_timer_create_basic() can also be used. This allows you to create a new timer without specifying any parameters.

A timer callback should have a void (*lv_timer_cb_t)(lv_timer_t *); prototype.

For example:

void my_timer(lv_timer_t * timer)
{
  /*Use the user_data*/
  uint32_t * user_data = timer->user_data;
  printf("my_timer called with user data: %d\n", *user_data);

  /*Do something with LVGL*/
  if(something_happened) {
    something_happened = false;
    lv_btn_create(lv_scr_act(), NULL);
  }
}

...

static uint32_t user_data = 10;
lv_timer_t * timer = lv_timer_create(my_timer, 500,  &user_data);

Ready and Reset

lv_timer_ready(timer) makes a timer run on the next call of lv_timer_handler().

lv_timer_reset(timer) resets the period of a timer. It will be called again after the defined period of milliseconds has elapsed.

Set parameters

You can modify some timer parameters later:

  • lv_timer_set_cb(timer, new_cb)

  • lv_timer_set_period(timer, new_period)

Repeat count

You can make a timer repeat only a given number of times with lv_timer_set_repeat_count(timer, count). The timer will automatically be deleted after it's called the defined number of times. Set the count to -1 to repeat indefinitely.

Measure idle time

You can get the idle percentage time of lv_timer_handler with lv_timer_get_idle(). Note that, it doesn't measure the idle time of the overall system, only lv_timer_handler. It can be misleading if you use an operating system and call lv_timer_handler in a timer, as it won't actually measure the time the OS spends in an idle thread.

Asynchronous calls

In some cases, you can't perform an action immediately. For example, you can't delete an object because something else is still using it, or you don't want to block the execution now. For these cases, lv_async_call(my_function, data_p) can be used to call my_function on the next invocation of lv_timer_handler. data_p will be passed to the function when it's called. Note that only the data pointer is saved, so you need to ensure that the variable will be "alive" while the function is called. It can be static, global or dynamically allocated data.

For example:

void my_screen_clean_up(void * scr)
{
  /*Free some resources related to `scr`*/

  /*Finally delete the screen*/
  lv_obj_del(scr);  
}

...

/*Do something with the object on the current screen*/

/*Delete screen on next call of `lv_timer_handler`, not right now.*/
lv_async_call(my_screen_clean_up, lv_scr_act());

/*The screen is still valid so you can do other things with it*/

If you just want to delete an object and don't need to clean anything up in my_screen_cleanup you could just use lv_obj_del_async which will delete the object on the next call to lv_timer_handler.

API

Typedefs

typedef void (*lv_timer_cb_t)(struct _lv_timer_t*)

Timers execute this type of functions.

typedef struct _lv_timer_t lv_timer_t

Descriptor of a lv_timer

Functions

void _lv_timer_core_init(void)

Init the lv_timer module

lv_timer_t *lv_timer_create_basic(void)

Create an "empty" timer. It needs to initialized with at least lv_timer_set_cb and lv_timer_set_period

Returns

pointer to the created timer

lv_timer_t *lv_timer_create(lv_timer_cb_t timer_xcb, uint32_t period, void *user_data)

Create a new lv_timer

Parameters
  • timer_xcb -- a callback to call periodically. (the 'x' in the argument name indicates that it's not a fully generic function because it not follows the func_name(object, callback, ...) convention)

  • period -- call period in ms unit

  • user_data -- custom parameter

Returns

pointer to the new timer

void lv_timer_del(lv_timer_t *timer)

Delete a lv_timer

Parameters

timer -- pointer to an lv_timer

void lv_timer_pause(lv_timer_t *timer)

Pause/resume a timer.

Parameters
  • timer -- pointer to an lv_timer

  • pause -- true: pause the timer; false: resume

void lv_timer_resume(lv_timer_t *timer)
void lv_timer_set_cb(lv_timer_t *timer, lv_timer_cb_t timer_cb)

Set the callback the timer (the function to call periodically)

Parameters
  • timer -- pointer to a timer

  • timer_cb -- the function to call periodically

void lv_timer_set_period(lv_timer_t *timer, uint32_t period)

Set new period for a lv_timer

Parameters
  • timer -- pointer to a lv_timer

  • period -- the new period

void lv_timer_ready(lv_timer_t *timer)

Make a lv_timer ready. It will not wait its period.

Parameters

timer -- pointer to a lv_timer.

void lv_timer_set_repeat_count(lv_timer_t *timer, int32_t repeat_count)

Set the number of times a timer will repeat.

Parameters
  • timer -- pointer to a lv_timer.

  • repeat_count -- -1 : infinity; 0 : stop ; n>0: residual times

void lv_timer_reset(lv_timer_t *timer)

Reset a lv_timer. It will be called the previously set period milliseconds later.

Parameters

timer -- pointer to a lv_timer.

void lv_timer_enable(bool en)

Enable or disable the whole lv_timer handling

Parameters

en -- true: lv_timer handling is running, false: lv_timer handling is suspended

uint8_t lv_timer_get_idle(void)

Get idle percentage

Returns

the lv_timer idle in percentage

lv_timer_t *lv_timer_get_next(lv_timer_t *timer)

Iterate through the timers

Parameters

timer -- NULL to start iteration or the previous return value to get the next timer

Returns

the next timer or NULL if there is no more timer

struct _lv_timer_t
#include <lv_timer.h>

Descriptor of a lv_timer

Public Members

uint32_t period

How often the timer should run

uint32_t last_run

Last time the timer ran

lv_timer_cb_t timer_cb

Timer function

void *user_data

Custom user data

int32_t repeat_count

1: One time; -1 : infinity; n>0: residual times

uint32_t paused

Typedefs

typedef void (*lv_async_cb_t)(void*)

Type for async callback.

Functions

lv_res_t lv_async_call(lv_async_cb_t async_xcb, void *user_data)

Call an asynchronous function the next time lv_timer_handler() is run. This function is likely to return before the call actually happens!

Parameters
  • async_xcb -- a callback which is the task itself. (the 'x' in the argument name indicates that it's not a fully generic function because it not follows the func_name(object, callback, ...) convention)

  • user_data -- custom parameter