1 1. Understanding FreeRTOS LCD Interfaces
2 2. Understanding FreeRTOS Touch Panel Interfaces
- 2.1 2.1. FreeRTOS Touch Panel Implementation
- 2.2 2.2. FreeRTOS Touch Panel C-Binding API
3 3. Understanding Sample GUI
- 3.1 3.1. Sample GUI Implementation
- 3.2 3.2. Sample GUI Session

This application note explains how to run a sample GUI on the LCD, from the FreeRTOS demo application.

1. Understanding FreeRTOS LCD Interfaces

1.1. FreeRTOS LCD Implementation

The FreeRTOS BSP makes use of the STM32CubeH7 software component to provide a device driver for the LCD controller. The driver is configured (enabled / disabled) at the BSP build time, using the HAL_LTDC_MODULE_ENABLED configuration option, defined in the stm32h7xx_hal_conf.h file.

The display video frame buffer resides in SDRAM, in a non-cached memory region. Depending on the value of the configGUI_INITIALIZED build-time parameter defined in the FreeRTOSConfig.h file, the driver initialises the LCD controller (configGUI_INITIALIZED is equal 1) or rely on the LCD controller settings defined by U-boot.

1.2. FreeRTOS LCD C-Binding API

The display driver implements the following C-binding API:

Function	Description	Comments
`uint8_t BSP_LCD_Init(void);`	Initialise LCD and backlight
`uint8_t BSP_LCD_DeInit(void);`	De-initialise LCD and backlight
`uint32_t BSP_LCD_GetXSize(void);`	Return LCD width in pixels
`uint32_t BSP_LCD_GetYSize(void);`	Return LCD height in pixels
`void BSP_LCD_LayerDefaultInit(uint16_t LayerIndex, uint32_t FrameBuffer);`	Set frame buffer address of layer `LayerIndex`
`void BSP_LCD_SelectLayer(uint32_t LayerIndex);`	Activate layer `LayerIndex`
`void BSP_LCD_Clear(uint32_t Color);`	Fill frame buffer with color Color
`void BSP_LCD_DisplayOn(void);`	Turn LCD on
`void BSP_LCD_DisplayOff(void);`	Turn LCD off
`void BSP_LCD_SetBrightness(uint8_t BrightnessValue);`	Set LCD brightness	`BrightnessValue` is from 0 (dimmest) to 100 (brightest)

1.3. LCD CLI Command

The FreeRTOS application implements the following display related CLI command:

Command	Description	Comments
`lcdtest`	Write a certain graphical pattern to the LCD display

2. Understanding FreeRTOS Touch Panel Interfaces

2.1. FreeRTOS Touch Panel Implementation

The FreeRTOS BSP makes use of the STM32CubeH7 software component to provide a device driver for the I2C touch controller. The driver is configured (enabled / disabled) at the BSP build time, using the HAL_I2C_MODULE_ENABLED configuration option, defined in the stm32h7xx_hal_conf.h file.

2.2. FreeRTOS Touch Panel C-Binding API

The touch driver implements the following C-binding API:

Function	Description	Comments

Function	Description	Comments
`ts_goodix_handler * ts_goodix_init(uint8_t bus, uint8_t i2c_addr, uint16_t max_width, uint16_t max_height, GPIO_TypeDef * port, uint32_t pin)`
	Initialize the I2C touch controller	`bus` is the I2C bus of the I2C touch controller; `i2c_addr` is the I2C address of the I2C touch controller on the specified I2C bus; `max_width` is a max width resolution of the touch screen; `max_height` is a max height resolution of the touch screen; `port` is the GPIO port which specify an interrupt of the I2C touch controller; `pin` is the GPIO pin which specify an interrupt of the I2C touch controller; returns the I2C touch controller handle or 0 in case of error
`int ts_goodix_read_input(ts_goodix_handler * hts, uint16_t * x, uint16_t * y)`
	Read data from the I2C touch controller	`hts` is the I2C touch controller handle; x is coordinates along the X-axis; `y` coordinates along the Y-axis; returns number of touches in case if the value is from 1 to 5 otherwise operation error (need to rerun the operation)

The ts_goodix_handler data structure used in the driver API has the following definition:

typedef struct {
   I2C_HandleTypeDef *  hi2c;       /* handle to the I2C interface */
   uint16_t             devid;      /* device id of the I2C touch controller */
   uint16_t             i2c_addr;   /* I2C address of the I2C touch controller */
   uint32_t             cfg_len;    /* length of the configuration data */
   uint16_t             max_width;  /* max width resolution */
   uint16_t             max_height; /* max heigth resolution */
} ts_goodix_handler;

3. Understanding Sample GUI

3.1. Sample GUI Implementation

The FreeRTOS test application implements a separate thread called GUI thread, which provides a sample GUI application running on the LCD display and the touch panel controller.

The sample GUI functions as follows:

Write a test pattern to the LCD display.
Initialise the touch controller driver, and then run an endless loop that waits for interrupts from the touch controller and, upon each touch event, print to the serial console a message with detailed information on the touch event.
In addition to the printing of the message with detailed information on the touch event, touching the display panel changes the shown picture between the two images. One of them is drawn using the DMA2D Chrom-Art Accelerator, the other fills the display frame buffer directly.

3.2. Sample GUI Session

Perform the following step-wise procedure, to validate the sample GUI functionality:

Power cycle the board and let it boot to the FreeRTOS CLI.
Validate that the test pattern is visible on the LCD display.
Validate that any touch to the display panel results in the correct coordinates (within the 480x272 constrains) printed to the serial console.
Validate that any touch to the display panel changes the shown picture between the two images.

Documentation

Running GUI on Display