Arduino H7 Video - LVGL9.X Double buffer is allocated but never used

[thodorii]

Hi, I've been running into what seems to be memory issues causing an MBED OS crash with LVGL. I was looking around to see draw buffer allocations and ran into this code. I am confused on the purpose of the 2nd draw buffer malloc when it is never used, is this an oversight?

Additionally, should this malloc size be multiplied by sizeof(lv_color_t) for the ideal lvgl recommendation of 1/10th buffer size

@facchinm
 

ArduinoCore-mbed/libraries/Arduino_H7_Video/src/Arduino_H7_Video.cpp

Lines 108 to 130 in f7ff411

	#if (LVGL_VERSION_MAJOR == 9)
	/* Create a draw buffer */
	static lv_color_t * buf1 = (lv_color_t*)malloc((width() * height() / 10)); /* Declare a buffer for 1/10 screen size */
	if (buf1 == NULL) {
	return 2; /* Insuff memory err */
	}
	static lv_color_t * buf2 = (lv_color_t*)malloc((width() * height() / 10)); /* Declare a buffer for 1/10 screen size */
	if (buf2 == NULL) {
	return 2; /* Insuff memory err */
	}
	lv_display_t *display;
	if(_rotated) {
	display = lv_display_create(height(), width());
	lv_display_set_rotation(display, LV_DISPLAY_ROTATION_270);
	//display->sw_rotate = 1;
	} else {
	display = lv_display_create(width(), height());
	}
	lv_display_set_buffers(display, buf1, NULL, width() * height() / 10, LV_DISPLAY_RENDER_MODE_PARTIAL); /*Initialize the display buffer.*/
	lv_display_set_flush_cb(display, lvgl_displayFlushing);
	lvgl_inc_thd.start(inc_thd);

[thodorii]

I can confirm that after disabling the second buffer, I no longer see the MBED OS crashes I used to consistently get on lv_timer_handler().

[leonardocavagnis]

Hi @thodorii
Yes, leaving there buf2 is probably an oversight.
Thanks for pointing it out!

But, I can't replicate the MBED OS crash. Please, could you post the sketch causing this?

[thodorii]

Unfortunately I don't think I can share the sketch due to it being part of work.

But the crash is likely due to memory constraints and the double buffer was the thing putting it in crashing territory.

The MBED OS crashes were happening with lv_timer_handler() and I was never able to get an exact trace of where it crashed.

[leonardocavagnis]

Ok, no problem! :)
I opened a PR with the suggested fix!

By the way, I decided not to increase the buffer size because, as suggested in the LVGL documentation, LV_DISPLAY_RENDER_MODE_PARTIAL can work with a buffer smaller than the display size.
I’m aware this could cause some stability issues, but increasing the buffer size would consume too much memory and lead to crashes.

[thodorii]

Ok great!

Anecdotally I also started seeing far fewer white screens after removing the buffer #1004 , although they were not completely gone.