CPU usage is always 99% and screen flickers if full_refresh equals 0

How-to
1

MCU: NXP MIMXRT1176DVMAA, with a MIPI screen
LVGL version:8.3.2

I’ve implement SDK examples:lvgl_guider_cm7 from NXP which enables vglite,but the cpu usage is 99% even there are only two labels and one button on the screen.

And the screen displays too slowly with about 500ms delay if I switch a focus from button to button.

Then I increase the vTaskDelay(1) to vTaskDelay(100) after lv_task_handler() in the main loop,cpu usage decreases to 30% or less(it’s changing,one second is 30%,one second is 50%,why?),but I don’t think it’s the issue.

I find that lv_task_handler() will execute about 700ms.

The most time consuming code is as below:

_lv_disp_refr_timer
	refr_invalid_areas
		refr_area
			refr_area_part(full_refresh == 1 branch)
refr_area_part
{
    ......
    else {
        /*Refresh the previous screen if any*/
        if(disp_refr->prev_scr) {
            if(top_prev_scr == NULL) top_prev_scr = disp_refr->prev_scr;
            refr_obj_and_children(draw_ctx, top_prev_scr); /* not executed */
        }

        if(top_act_scr == NULL) top_act_scr = disp_refr->act_scr;
        /* take up to 600ms! */
        refr_obj_and_children(draw_ctx, top_act_scr);
    }
    /*Also refresh top and sys layer unconditionally*/
    /* take up to 100ms! */
    refr_obj_and_children(draw_ctx, lv_disp_get_layer_top(disp_refr));
    refr_obj_and_children(draw_ctx, lv_disp_get_layer_sys(disp_refr));
    draw_buf_flush(disp_refr);
}

the function refr_obj_and_children is so time-consuming.What can I do to speed the function?

By the way,the screen will flicker from one incomplete screen to another if I set full_refresh to 0.How can I fix this?

2

all right,I’ve solved the 99% issue by setting the Optimize Level to -O3.Now cpu usage is 50%.
1.I wonder how it affects the cpu usage?Is it normal that the cpu usage is 99% if I don’t optimize the code?
2.And also,the screen will flicker from one incomplete screen to another if I set full_refresh to 0.How can I fix this?

3

Seems your config isnt good. Try start with buffers and display driver config.
Next show cb funcs . You write MIPI , this can be hires for example 1280x720 and manage this isnt simple job.

4

Is that normal the cpu usage is 99% if I don’t optimize code?
The resolution of the screen is 480x640.The flush_cb doesn’t take a lot of time,about 10ms.
I’ve tried to set LV_MEM_SIZE,LV_MEM_BUF_MAX_NUM,LV_LAYER_SIMPLE_BUF_SIZE,LV_LAYER_SIMPLE_FALLBACK_BUF_SIZE to big,but all don’t work.
refr_obj_and_children takes a lot of time,is that relevant to the MIPI config?

disp_drv.flush_cb = DEMO_FlushDisplay;

static void DEMO_FlushDisplay(lv_disp_drv_t *disp_drv, const lv_area_t *area, lv_color_t *color_p)
{
    DEMO_FLUSH_DCACHE();
    g_dc.ops->setFrameBuffer(&g_dc, 0, (void *)color_p);  //DC_FB_LCDIFV2_SetFrameBuffer
	/* wait for a semaphore gived in DC_FB_LCDIFV2_IRQHandler */
    DEMO_WaitBufferSwitchOff();
    lv_disp_flush_ready(disp_drv);
}

status_t DC_FB_LCDIFV2_SetFrameBuffer(const dc_fb_t *dc, uint8_t layer, void *frameBuffer)
{
    assert(layer < DC_FB_LCDIFV2_MAX_LAYER);
    dc_fb_lcdifv2_handle_t *dcHandle = dc->prvData;

    LCDIFV2_SetLayerBufferAddr(dcHandle->lcdifv2, layer, (uint32_t)(uint8_t *)frameBuffer);
    dcHandle->layers[layer].inactiveBuffer = frameBuffer;
	
    if (dcHandle->layers[layer].enabled)
    {
        LCDIFV2_TriggerLayerShadowLoad(dcHandle->lcdifv2, layer);
        dcHandle->layers[layer].shadowLoadPending = true;
        dcHandle->layers[layer].framePending      = true;
    }
    return kStatus_Success;
}

For full_refresh=0,the screen flickers,it seems the issue of the LCD controller,but I’ve no idea.

5

Im not expert for NXP, but hw based (video mipi mode) displays control require direct mode in lvgl. If your MIPI is in command mode = high speed SPI
Read docu about it.
In direct mode flush_cb require only line lv_disp_flush_ready(disp_drv);

6

Hi,
Regarding the CPU usage, to keep system responsive, please use a suitable vTaskDelay value. more details, please refer to Timer Handler — LVGL documentation

As I know the MIMXRT1176DVMAA large panel(1280x720) doesn’t support partial refresh. so you can’t change the full_refresh to 0.