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
andlv_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
-
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
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