SDAA158 December   2025 MSPM33C321A

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Overview
    1. 1.1 LVGL Project Setup
    2. 1.2 Configuration
    3. 1.3 Initialization
    4. 1.4 LVGL Output
    5. 1.5 LVGL Input
    6. 1.6 LVGL Update
  5. 2LVGL Example
    1. 2.1 Hardware Connections
    2. 2.2 Software
    3. 2.3 LVGL Example Summary
  6. 3Summary
  7. 4Revision History

1.3 Initialization

When creating an embedded GUI using LVGL, the display being used must be initalized and LVGL must be configured to work with the display. This initalization and configuration is done through the LVGL global function lv_port_disp_init. This function is broken into three sections:

  • Display Initalization
    • LVGL includes a global function, disp_init. This function is called in lv_port_disp_init and can be used to trigger the initalization sequence for the display being used.
  • Color Buffer Allocation and Refresh Mode Selection
    • LVGL uses a color buffer to store the pixel data for a rendered image. This buffer, lv_disp_draw_buf_t, is allocated in lv_port_disp_init. There are two typical buffering configurations:
      • Single Buffer: A single buffer is allocated and passed into lv_disp_draw_buf_init. The size of this buffer is typically ten times the horizontal resultion (10 rows of pixels). This buffer is solely populated with the pixel data for a rendered image and the CPU is responsible for transfering the color buffer's pixel information to the communication interface used to communication with the display.
      • Double Buffer with DMA: Two buffers are allocated with the same amount of memory and passed into lv_disp_draw_buf_init. The size of both buffers is typically 10 rows of pixels. LVGL populates one buffer with part of the pixel data for a rendered image and then makes the data available for the DMA to begin transfering data to the communication interface.
    • There are, also, two modes to configure how LVGL performs image refreshes:
      • Partial Refresh: In partial refresh, only the portion of the rendered image that is being updated is written to the color buffer. This is enabled by default. This mode allows for faster refreshes and a smaller color buffer, however, can result in residual display artifacts if the display is partial to tearing or banding.
      • Full Refresh: In full refresh, the entire rendered image is written to the color buffer. This is enabled by setting the full_refresh field in the lv_disp_drv_t display driver. This mode elimiates the issue of residual display artificacts, but is much slower and requires a color buffer that is equal to the resolution of the screen.
  • Display Driver Configuration
    • LVGL provides a display driver structure that must be configured so that LVGL properly renders the display. The first step is initializing the display driver by calling lv_disp_drv_init with a new instance of the driver, lv_disp_drv_t
    • After the display driver has been initalized, the main values that must be configured are:
      • The horizontal and veritical resolutions: The horizontal and vertical resolutions, hor_res and ver_res, are members of the display driver and can be set with the previously defined MY_DISP_HOR_RES and MY_DISP_VER_RES
      • The flush callback: The display driver must be configured with the location of the flush callback, flush_cb. The flush callback is the method that is called when LVGL is to flush the color buffer that has been populated with the pixel data of the rendered image. This callback method is discussed further in this application note
      • The draw buffer: The display driver must be configured with the location of the color buffer that was previosuly initalized, draw_buf
      • The refresh mode: If using the full refresh mode, the display driver must be configured with full_refresh being set to 1
    • Finally, the display driver must be registered with LVGL, by calling lv_disp_drv_register

LVGL has support for several types of input devices, including a touchpad, mouse, keypad, encoder, or button. All of these input devices must initalized and configured with LVGL. This is performed in the LVGL global function lv_port_indev_init, and is broken into two sections:

  • Input Device Initalization
    • LVGL includes several global functions that can be used to initalize the input device. For example, when using a display that has either resistive or capacitve touch, the global function touchpad_init can be called to perform the touchpad initialization.
  • Input Device Driver Configuration
    • LVGL provides an input device driver structure that must be configured so that LVGL properly processes inputs. The first step is initializing the input device driver by calling lv_indev_drv_init with a new instance of the driver, lv_indev_drv_t
    • After the input device driver has been initalized, the main values that must be configured are:
      • The input device type: The type of input device being used: pointer (touchpad or mouse), keypad, button, and encoder
      • The input read callback: The input device driver must be configured with the location of the input read callback, read_cb. The input read callback is the method that is called when LVGL is to read for any input from the input device. This callback method is discussed further in this application note
    • Finally, the input device driver must be registered with LVGL, by calling lv_indev_drv_register