Timer (lv_timer)
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 Timer Handler 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_button_create(lv_screen_active(), 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.
Enable and Disable
You can enable or disable a timer with lv_timer_enable(en).
Pause and Resume
lv_timer_pause(timer) pauses the specified timer.
lv_timer_resume(timer) resumes the specified timer.
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.
Timer handler resume callback
When the lv_timer_handler is stopped, if you want to pay attention to the wake-up
timing of the lv_timer_handler, you can set a resume callback using
lv_timer_handler_set_resume_cb(cb, user_data).
The callback should have a void (*lv_timer_handler_resume_cb_t)(void*) prototype.
Asynchronous calls
In some cases, you can't perform an action immediately. For example, you
can't delete a Widget 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. If you want to cancel an asynchronous
call, call lv_async_call_cancel(my_function, data_p), which will
clear all asynchronous calls matching my_function and data_p.
For example:
void my_screen_clean_up(void * scr)
{
/* Free some resources related to `scr`*/
/* Finally delete the screen */
lv_obj_delete(scr);
}
...
/* Do something with the Widget on the current screen */
/* Delete screen on next call of `lv_timer_handler`, not right now. */
lv_async_call(my_screen_clean_up, lv_screen_active());
/* The screen is still valid so you can do other things with it */
If you just want to delete a Widget and don't need to clean anything up
in my_screen_cleanup you could just use lv_obj_delete_async() which
will delete the Widget on the next call to lv_timer_handler().