tests: add LittlevGL test application

tests/pkg_lvgl/Makefile

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+BOARD ?= stm32f429i-disc1
+include ../Makefile.tests_common
+
+# No interactive_sync
+DISABLE_MODULE += test_utils_interactive_sync
+
+USEPKG += lvgl
+USEMODULE += lvgl_contrib
+USEMODULE += ili9341
+
+include $(RIOTBASE)/Makefile.include

tests/pkg_lvgl/Makefile.ci

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+BOARD_INSUFFICIENT_MEMORY := \
+    blackpill \
+    bluepill \
+    i-nucleo-lrwan1 \
+    nucleo-f031k6 \
+    nucleo-f042k6 \
+    nucleo-f302r8 \
+    nucleo-f303k8 \
+    nucleo-f334r8 \
+    nucleo-l031k6 \
+    nucleo-l053r8 \
+    saml10-xpro \
+    saml11-xpro \
+    stm32f030f4-demo \
+    stm32f0discovery \
+    stm32l0538-disco \
+    #

tests/pkg_lvgl/README.md

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+LittlevGL sample application
+============================
+
+This application shows a basic usage of LittlevGL with RIOT. It's simply an
+adaption of one of the upstream examples: the
+[sysmon example](https://github.com/littlevgl/lv_examples/tree/master/lv_apps/sysmon).
+
+### Flashing the application
+
+The application works without modification on the stm32f429i-disc1 board. To
+build, flash and run the application for this board, just use:
+
+```
+make BOARD=stm32f429i-disc1 -C tests/pkg_lvgl flash
+```
+
+### Expected result
+
+The application displays a basic system monitor with the CPU and memory
+usage of the board.
+Note that on the pinetime, due to a too small screen resolution, some
+information is cropped.

tests/pkg_lvgl/main.c

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+/*
+ * Copyright (C) 2019 Inria
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       LittlevGL example application
+ *
+ * @author      Alexandre Abadie <alexandre.abadie@inria.fr>
+ *
+ * @}
+ */
+
+#include <string.h>
+
+#include "xtimer.h"
+
+#include "lvgl/lvgl.h"
+#include "lvgl_riot.h"
+
+#include "ili9341.h"
+#include "ili9341_params.h"
+#include "disp_dev.h"
+#include "ili9341_disp_dev.h"
+
+static ili9341_t dev;
+
+#define CPU_LABEL_COLOR     "FF0000"
+#define MEM_LABEL_COLOR     "0000FF"
+#define CHART_POINT_NUM     100
+
+/* Must be lower than LVGL_INACTIVITY_PERIOD_MS for autorefresh */
+#define REFR_TIME           200
+
+static lv_obj_t *win;
+static lv_obj_t *chart;
+static lv_chart_series_t * cpu_ser;
+static lv_chart_series_t *mem_ser;
+static lv_obj_t *info_label;
+static lv_task_t *refr_task;
+
+static void sysmon_task(lv_task_t *param)
+{
+    (void)param;
+
+    /* Get CPU and memory information */
+    uint8_t cpu_busy = 100 - lv_task_get_idle();
+
+    lv_mem_monitor_t mem_mon;
+    lv_mem_monitor(&mem_mon);
+
+    uint8_t mem_used_pct = mem_mon.used_pct;
+
+    /* Add the CPU and memory data to the chart */
+    lv_chart_set_next(chart, cpu_ser, cpu_busy);
+    lv_chart_set_next(chart, mem_ser, mem_used_pct);
+
+    /* Set the text info */
+    lv_label_set_text_fmt(info_label,
+                          "%s%s CPU: %d %%%s\n\n"
+                          LV_TXT_COLOR_CMD"%s MEMORY: %d %%"LV_TXT_COLOR_CMD"\n"
+                          "Total: %d bytes\n"
+                          "Used: %d bytes\n"
+                          "Free: %d bytes\n"
+                          "Frag: %d %%",
+                          LV_TXT_COLOR_CMD,
+                          CPU_LABEL_COLOR,
+                          cpu_busy,
+                          LV_TXT_COLOR_CMD,
+                          MEM_LABEL_COLOR,
+                          mem_used_pct,
+                          (int)mem_mon.total_size,
+                          (int)mem_mon.total_size - mem_mon.free_size,
+                          mem_mon.free_size, mem_mon.frag_pct);
+
+    /* Force a wakeup of lvgl when each task is called: this ensures an activity
+       is triggered and wakes up lvgl during the next LVGL_INACTIVITY_PERIOD ms */
+    lvgl_wakeup();
+}
+
+void sysmon_create(void)
+{
+    refr_task = lv_task_create(sysmon_task, REFR_TIME, LV_TASK_PRIO_LOW, NULL);
+
+    lv_coord_t hres = lv_disp_get_hor_res(NULL);
+    lv_coord_t vres = lv_disp_get_ver_res(NULL);
+
+    win = lv_win_create(lv_disp_get_scr_act(NULL), NULL);
+    lv_win_set_title(win, "System monitor");
+
+    /* Make the window content responsive */
+    lv_win_set_layout(win, LV_LAYOUT_PRETTY);
+
+    /* Create a chart with two data lines */
+    chart = lv_chart_create(win, NULL);
+    lv_obj_set_size(chart, hres / 2, vres / 2);
+    lv_obj_set_pos(chart, LV_DPI / 10, LV_DPI / 10);
+    lv_chart_set_point_count(chart, CHART_POINT_NUM);
+    lv_chart_set_range(chart, 0, 100);
+    lv_chart_set_type(chart, LV_CHART_TYPE_LINE);
+    lv_chart_set_series_width(chart, 4);
+    cpu_ser = lv_chart_add_series(chart, LV_COLOR_RED);
+    mem_ser = lv_chart_add_series(chart, LV_COLOR_BLUE);
+
+    /* Set the data series to zero */
+    uint16_t i;
+    for(i = 0; i < CHART_POINT_NUM; i++) {
+        lv_chart_set_next(chart, cpu_ser, 0);
+        lv_chart_set_next(chart, mem_ser, 0);
+    }
+
+    /* Create a label for the details of Memory and CPU usage */
+    info_label = lv_label_create(win, NULL);
+    lv_label_set_recolor(info_label, true);
+    lv_obj_align(info_label, chart, LV_ALIGN_OUT_RIGHT_TOP, LV_DPI / 4, 0);
+
+    /* Refresh the chart and label manually at first */
+    sysmon_task(NULL);
+}
+
+int main(void)
+{
+    /* Configure the generic display driver interface */
+    disp_dev_t *disp_dev = (disp_dev_t *)&dev;
+    disp_dev->driver = &ili9341_disp_dev_driver;
+
+    /* Initialize the concrete display driver */
+    ili9341_init(&dev, &ili9341_params[0]);
+
+    /* Initialize lvgl with the generic display driver interface */
+    lvgl_init(disp_dev);
+
+    /* Create the system monitor widget */
+    sysmon_create();
+
+    return 0;
+}