CPU overload when showing sensor data on screen

How-to
1

Hi,

I am running a code on ESP IDE for WT32-SC01 Plus Touch LCD which has a ESP32 S3 MCU.
I am displaying 60 float numbers on a page that is under menu section of my UI. The way I hav implemented it works but it seems super inefficient and I can see my LCD is struggling to update the numbers (CPU usage goes to 98%). How ever, I can not find any other way to do it. Can anyone suggest a better way?

Here is the simplified code:

void Rate_0(void *pvParameter)
{
	           TickType_t xLastWakeTime0;
		    const TickType_t xFrequency = 1 / portTICK_PERIOD_MS; // 1000 Hz
		    xLastWakeTime0 = xTaskGetTickCount();

		    char str[25];

	 while (1) {

	       lv_timer_handler();

	                                      sprintf(str, "Status: %.2f", *(IncomingData485 +0)); 
	       		                      lv_label_set_text(ui_Status, str);
	       		                      sprintf(str, "ArmPos1: %.2f", *(IncomingData485 +1)); 
	       		                      lv_label_set_text(ui_ArmPos1, str);
	       		                      sprintf(str, "ArmPos2: %.2f", *(IncomingData485 +2)); 
	       		                      lv_label_set_text(ui_ArmPos2, str);
.
.
.
	       		                      sprintf(str, "ArmPos58: %.2f", *(IncomingData485 +58)); 
	       		                      lv_label_set_text(ui_ArmPos58, str);
	       		                      sprintf(str, "ArmPos59: %.2f", *(IncomingData485 +59)); 
	       		                      lv_label_set_text(ui_ArmPos59, str);

	    	vTaskDelayUntil(&xLastWakeTime0, xFrequency);
	    }
}

extern "C" void app_main(void)
{
	  /* Initialize model */
   init_lvgl_lgfx();
    ui_init();


	  xTaskCreate(Rate_0, "Rate_0", 10240 , NULL, configMAX_PRIORITIES-1,NULL);

               }

As you can, these numbers are getting updated 1000 times per second in my loop. However, I do not need them to be updated all the time. I only want them updated when I go to that specific page in my menu UI. when I actually try to see them.

How can I make them run only when that page is showing?
Is it even an efficient way to put the number in a string then use “lv_label_set_text” to update it on screen? is there any other way?

PS. The code freaks out if I take the “lv_label_set_text” functions out of “lv_timer_handler” task and put it in another task with a different rate or even if I put them all in an “if” condition that makes it run less frequent. Not sure why that happens. By freaking out I mean it interrupts other features in my code and they wont work properly.

2

It is recommended to use timer to control the text refresh cycle instead of placing it directly in the lvgl main loop. Reference document:Timers — LVGL documentation
You can refer to the code below:

static void sensor_update_timer(lv_timer_t* timer)
{
	lv_label_set_text_fmt(ui_Status, "Status: %.2f", *(IncomingData485 + 0));
	...
	lv_label_set_text_fmt(ui_ArmPos59, "ArmPos59: %.2f", *(IncomingData485 + 59));
}

void Rate_0(void *pvParameter)
{
    TickType_t xLastWakeTime0;
    const TickType_t xFrequency = 1 / portTICK_PERIOD_MS; // 1000 Hz
    xLastWakeTime0 = xTaskGetTickCount();

    lv_timer_create(sensor_update_timer, 100, NULL);

    while (1) {
        lv_timer_handler();
        vTaskDelayUntil(&xLastWakeTime0, xFrequency);
    }
}

In addition, LVGL’s API cannot be used across threads, which may lead to thread safety issues. Reference document: Operating system and interrupts — LVGL documentation.

1 Like
3

I think your TickType_t is a int or an int32_t or something. But if you divide 1 / portTICK_PERIOD_MS the result is probably 0. So no delay and high CPU load.

Just do xFrequency = 1

Also if you want to use multi core, you have to put a mutex in front of lv_timer_handler() and lock it when you update the labels.

1 Like
4

Thank you soo much for your help.
I have been asking this question 3 different ways within the last 3 months. Finally you answered it and saved me a lot of time. My code runs perfectly after your suggestion.
I also did not know about the " lv_label_set_text_fmt " command. much more efficient.