Delete old values in chart (memory overflow problem)

How-to
1

Description

I have a chart with shifting values. Somehow the memory overflows at 72% usage and the display freezes. I think it’s because the values don’t get deleted with lv_chart_set_next_value. How would it be possible to delete the last values in the chart manually?

What MCU/Processor/Board and compiler are you using?

ESP32S3 Touch Display, framework: Arduino

What LVGL version are you using?

8.3.4

What do you want to achieve?

That the display works.

What have you tried so far?

I thought the old values would be deleted automatically with lv_chart_set_next_value. I searched in the lv_chart.c for functions which i could use.

init code

chart_main = lv_chart_create(tab2);
  lv_obj_set_size(chart_main, 400, 200);
  lv_obj_center(chart_main);
  lv_obj_align(chart_main, LV_ALIGN_TOP_MID, 30, 0);
  lv_chart_set_type(chart_main, LV_CHART_TYPE_LINE); /*Show lines and points too*/
  lv_chart_set_update_mode(chart_main, LV_CHART_UPDATE_MODE_SHIFT);
  lv_chart_set_range(chart_main, LV_CHART_AXIS_PRIMARY_Y, 0, 150);
  lv_obj_add_event_cb(chart_main, draw_event_cb_chart_x_axis, LV_EVENT_DRAW_PART_BEGIN, NULL);
  lv_obj_add_event_cb(chart_main, draw_event_cb_chart_y_axis, LV_EVENT_DRAW_PART_BEGIN, NULL);

  // Add  data series
  ser_voltage_60s = lv_chart_add_series(chart_main, lv_palette_main(LV_PALETTE_BLUE), LV_CHART_AXIS_PRIMARY_Y);
  ser_voltage_600s = lv_chart_add_series(chart_main, lv_palette_main(LV_PALETTE_BLUE), LV_CHART_AXIS_PRIMARY_Y);
  ser_voltage_3600s = lv_chart_add_series(chart_main, lv_palette_main(LV_PALETTE_BLUE), LV_CHART_AXIS_PRIMARY_Y);

code

 lv_chart_set_next_value(chart_main, ser_voltage_600s, average_voltage_600s_value);
 lv_chart_set_next_value(chart_main, ser_current_600s, average_current_600s_value);
 lv_chart_set_next_value(chart_main, ser_power_600s, average_power_600s_value);
 lv_chart_set_next_value(chart_main, ser_temp_600s, average_temp_600s_value);
 lv_chart_refresh(chart_main);

Screenshot and/or video

image_2024-08-22_110232841
image_2024-08-22_1102328411536×2048 269 KB

2

Hello,

Best option is probably not to delete old values but simply overwrite them if that is possible for you.
You will have to maintain some sort of rolling buffer for this.

From the documentation: Chart (lv_chart) — LVGL documentation

Set the values manually in the array like ser1->points[3] = 7 and refresh the chart with lv_chart_refresh(chart)

I believe continually using set_next_value just makes your buffer bigger and bigger…

3

Hi Tinus,

Thank you for your help! The issue has been resolved. It turned out that a style was being repeatedly defined, which caused the overflow.

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