# STM32 — LVGL documentation

# STM32

LVGL Can be added to STM32CubeIDE in a similar fashion to any other Eclipse-based IDE.

## Including LVGL in a Project

- Create or open a project in STM32CubeIDE.

- Copy the entire LVGL folder to [project_folder]/Drivers/lvgl.

- In the STM32CubeIDE Project Explorer pane: right click on the LVGL folder that you copied (you may need to refresh the view first before it will appear), and select Add/remove include path…. If this doesn't appear, or doesn't work, you can review your project include paths under the Project -> Properties menu, and then navigating to C/C++ Build -> Settings -> Include paths, and ensuring that the LVGL directory is listed.

Now that the source files are included in your project, follow the instructions for Porting your project to create the `lv_conf.h` file, and initialise the display.

## Bare Metal Example

A minimal example using STM32CubeIDE, and HAL. * When setting up Pinout and Configuration using the Device Configuration Tool, select System Core -> SYS and ensure that Timebase Source is set to SysTick. * Configure any other peripherals (including the LCD panel), and initialise them in main.c. * `#include "lvgl.h"` in the main.c file. * Create some frame buffer(s) as global variables:

    //Frame buffers
    /*Static or global buffer(s). The second buffer is optional*/
    static lv_color_t buf_1[BUFF_SIZE]; //TODO: Chose a buffer size. DISPLAY_WIDTH * 10 is one suggestion.
    static lv_color_t buf_2[BUFF_SIZE];

- In your `main()` function, after initialising your CPU, peripherals, and LCD panel, call `lv_init()` to initialise LVGL. You can then create the display driver using `lv_disp_create()`, and register the frame buffers using `lv_disp_set_draw_buffers()`.

    //Initialise LVGL UI library
    lv_init();

    lv_disp_t * disp = lv_disp_create(WIDTH, HEIGHT); /*Basic initialization with horizontal and vertical resolution in pixels*/
    lv_disp_set_flush_cb(disp, my_flush_cb); /*Set a flush callback to draw to the display*/
    lv_disp_set_draw_buffers(disp, buf_1, buf_2, sizeof(buf_1), LV_DISP_RENDER_MODE_PARTIAL); /*Set an initialized buffer*/

- Create some dummy objects to test the output:

    // Change the active screen's background color
    lv_obj_set_style_bg_color(lv_screen_active(), lv_color_hex(0x003a57), LV_PART_MAIN);
    lv_obj_set_style_text_color(lv_screen_active(), lv_color_hex(0xffffff), LV_PART_MAIN);

    /*Create a spinner*/
    lv_obj_t * spinner = lv_spinner_create(lv_screen_active(), 1000, 60);
    lv_obj_set_size(spinner, 64, 64);
    lv_obj_align(spinner, LV_ALIGN_BOTTOM_MID, 0, 0);

- Add a call to `lv_timer_handler()` inside your `while(1)` loop:

    /* Infinite loop */
    while (1)
    {
      lv_timer_handler();
      HAL_Delay(5);
    }

- Add a call to `lv_tick_inc()` inside the `SysTick_Handler()` function. Open the stm32xxxx_it.c file (the name will depend on your specific MCU), and update the `SysTick_Handler()` function:

    void SysTick_Handler(void)
    {
      /* USER CODE BEGIN SysTick_IRQn 0 */

        HAL_SYSTICK_IRQHandler();
        lv_tick_inc(1);
        #ifdef USE_RTOS_SYSTICK
          osSystickHandler();
        #endif

      /* USER CODE END SysTick_IRQn 0 */
      HAL_IncTick();
      /* USER CODE BEGIN SysTick_IRQn 1 */

      /* USER CODE END SysTick_IRQn 1 */
    }

- Finally, write the callback function, `my_flush_cb`, which will send the display buffer to your LCD panel. Below is one example, but it will vary depending on your setup.

    void my_flush_cb(lv_disp_t * disp, const lv_area_t * area, lv_color_t * color_p)
    {
      //Set the drawing region
      set_draw_window(area->x1, area->y1, area->x2, area->y2);

      int height = area->y2 - area->y1 + 1;
      int width = area->x2 - area->x1 + 1;

      //We will do the SPI write manually here for speed
      HAL_GPIO_WritePin(DC_PORT, DC_PIN, GPIO_PIN_SET);
      //CS low to begin data
      HAL_GPIO_WritePin(CS_PORT, CS_PIN, GPIO_PIN_RESET);

      //Write colour to each pixel
      for (int i = 0; i < width * height; i++) {
        uint16_t color_full = (color_p->red << 11) | (color_p->green << 5) | (color_p->blue);
        parallel_write(color_full);

        color_p++;
      }

      //Return CS to high
      HAL_GPIO_WritePin(CS_PORT, CS_PIN, GPIO_PIN_SET);

      /* IMPORTANT!!!
      * Inform the graphics library that you are ready with the flushing*/
      lv_disp_flush_ready(disp);
    }

## FreeRTOS Example

A minimal example using STM32CubeIDE, HAL, and CMSISv1 (FreeRTOS). Note that we have not used Mutexes in this example, however LVGL is NOT thread safe and so Mutexes should be used. See: Operating system and interrupts * `#include "lvgl.h"` * Create your frame buffer(s) as global variables:

    //Frame buffers
    /*A static or global variable to store the buffers*/
    static lv_disp_draw_buf_t disp_buf;

    /*Static or global buffer(s). The second buffer is optional*/
    static lv_color_t buf_1[BUFF_SIZE]; //TODO: Declare your own BUFF_SIZE appropriate to your system.
    static lv_color_t buf_2[BUFF_SIZE];

- In your `main` function, after your peripherals (SPI, GPIOs, LCD etc) have been initialised, initialise LVGL using `lv_init()`, register the frame buffers using `lv_disp_draw_buf_init()`, and create a new display driver using `lv_disp_drv_init()`.

    //Initialise LVGL UI library
    lv_init();
    lv_disp_draw_buf_init(&disp_buf, buf_1, buf_2, BUFF_SIZE);

    static lv_disp_drv_t disp_drv;          /*A variable to hold the drivers. Must be static or global.*/
    lv_disp_drv_init(&disp_drv);            /*Basic initialization*/
    disp_drv.draw_buf = &disp_buf;          /*Set an initialized buffer*/
    disp_drv.flush_cb = my_flush_cb;        /*Set a flush callback to draw to the display*/
    disp_drv.hor_res = WIDTH;                 /*Set the horizontal resolution in pixels*/
    disp_drv.ver_res = HEIGHT;                 /*Set the vertical resolution in pixels*/

    lv_disp_t * disp;
    disp = lv_disp_drv_register(&disp_drv); /*Register the driver and save the created display objects*/

    // Register the touch controller with LVGL - Not included here for brevity.

- Create some dummy objects to test the output:

    // Change the active screen's background color
    lv_obj_set_style_bg_color(lv_screen_active(), lv_color_hex(0x003a57), LV_PART_MAIN);
    lv_obj_set_style_text_color(lv_screen_active(), lv_color_hex(0xffffff), LV_PART_MAIN);

    /*Create a spinner*/
    lv_obj_t * spinner = lv_spinner_create(lv_screen_active(), 1000, 60);
    lv_obj_set_size(spinner, 64, 64);
    lv_obj_align(spinner, LV_ALIGN_BOTTOM_MID, 0, 0);

- Create two threads to call `lv_timer_handler()`, and `lv_tick_inc()`.You will need two `osThreadId` handles for CMSISv1. These don't strictly have to be globally accessible in this case, however STM32Cube code generation does by default. If you are using CMSIS and STM32Cube code generation it should look something like this:

    //Thread Handles
    osThreadId lvgl_tickHandle;
    osThreadId lvgl_timerHandle;

    /* definition and creation of lvgl_tick */
    osThreadDef(lvgl_tick, LGVLTick, osPriorityNormal, 0, 1024);
    lvgl_tickHandle = osThreadCreate(osThread(lvgl_tick), NULL);

    //LVGL update timer
    osThreadDef(lvgl_timer, LVGLTimer, osPriorityNormal, 0, 1024);
    lvgl_timerHandle = osThreadCreate(osThread(lvgl_timer), NULL);

- And create the thread functions:

    /* LVGL timer for tasks. */
    void LVGLTimer(void const * argument)
    {
      for(;;)
      {
        lv_timer_handler();
        osDelay(20);
      }
    }
    /* LVGL tick source */
    void LVGLTick(void const * argument)
    {
      for(;;)
      {
        lv_tick_inc(10);
        osDelay(10);
      }
    }

- Finally, create the `my_flush_cb` function to output the frame buffer to your LCD. The specifics of this function will vary depending on which MCU features you are using. Below is an example for a typical MCU interface.

    void my_flush_cb(lv_disp_drv_t * disp_drv, const lv_area_t * area, lv_color_t * color_p)
    {
      //Set the drawing region
      set_draw_window(area->x1, area->y1, area->x2, area->y2);

      int height = area->y2 - area->y1 + 1;
      int width = area->x2 - area->x1 + 1;

      //Begin SPI Write for DATA
      HAL_GPIO_WritePin(DC_PORT, DC_PIN, GPIO_PIN_SET);
      HAL_GPIO_WritePin(CS_PORT, CS_PIN, GPIO_PIN_RESET);

      //Write colour to each pixel
      for (int i = 0; i < width * height; i++) {
          parallel_write(color_p->full);
          color_p++;
      }

      //Return CS to high
      HAL_GPIO_WritePin(CS_PORT, CS_PIN, GPIO_PIN_SET);

      /* IMPORTANT!!!
       * Inform the graphics library that you are ready with the flushing*/
      lv_disp_flush_ready(disp_drv);
    }