Display module framework introduction

Overview

SiFli’s display framework is based on the rt_device framework and has the following features:

  • The same display driver, TP driver, and backlight driver can be reused across different development boards.

  • The same development board can select different display modules through menuconfig.

  • Supports compatibility with multiple display drivers and TP drivers at the same time, distinguished by ID.



This design does improve reuse, but it also introduces the issue of dispersion in display module driver configuration:

  • The display module power-on/power-off, reset interface, pinmux settings, PWM used by the backlight, and other code are associated with the development board (similar to the BIOS of the display driver module).

  • Display driver, TP driver, and backlight driver implementations must be based on the macro definitions and IO interfaces provided above.

  • Finally, consolidate the implemented display driver, TP driver, and backlight driver into one menuconfig menu for board selection.



Display section

Display framework diagram

alt text

Explanation of each item in the figure:

  • Driver layer (drv_lcd.c) — implements an rt_device named “lcd” for the upper layer to operate the display.

  • Specific driver code in the middle green section (the main code for adding a display driver for customers)

  • Board-level IO interface file (bsp_lcd_tp.c, or drv_io.c) — provides unified power-on, power-off, and reset interfaces for the display driver.

  • Backlight device “lcdlight” — provides a unified backlight control interface for the display driver.

  • HAL layer (bf0_hal_lcdc.c) — provides basic unified interfaces for parameter configuration, LCD register read/write, and other operations for the display driver.





Register the screen driver to the system

SiFli’s display driver framework supports registering multiple display drivers to the system at the same time. The macro LCD_DRIVER_EXPORT2 generates variables with a special section name and links them together.

In nv3051f1.c, LCD_DRIVER_EXPORT2 is used to register the callback functions of the display driver to the system. For detailed analysis of each function, refer to Display driver callback functions:

static const LCD_DrvOpsDef LCD_drv =
{
	LCD_Init,    			  //【必选】，屏驱初始函数(包括复位，初始化程序等) 
	LCD_ReadID,    			  //【必选】，Display presence detection函数 
	LCD_DisplayOn,   		  //【必选】，屏幕打开 
	LCD_DisplayOff,  		  //【必选】，屏幕关闭 
	LCD_SetRegion,    		  //【必选】，设置屏幕接受数据时的区域（2A,2B 的区域）
	LCD_WritePixel,   		  // 可选，写一个像素点到屏幕上
	LCD_WriteMultiplePixels,  //【必选】，写批量像素点到屏幕上
	LCD_ReadPixel,    		  // 可选，读屏幕上的一个像素点数据，返回像素的RGB值
	LCD_SetColorMode,    	  // 可选，切换输出给屏幕的颜色格式
	LCD_SetBrightness,   	  // 可选，设置屏幕的亮度 
	LCD_IdleModeOn,    		  // 可选，进入待机显示模式（低功耗模式） 
	LCD_IdleModeOff,   		  // 可选，退出待机显示模式（低功耗模式） 
	LCD_Rotate,  			  // 可选，旋转屏幕一定角度 
	LCD_TimeoutDbg, 		  // 可选，批量送数超时后，屏幕自检 
	LCD_TimeoutReset,  		  // 可选，批量送数超时后，屏幕复位 
	LCD_ESDCheck,  		      // 可选，屏幕定时ESD检测 
};

LCD_DRIVER_EXPORT2(nv3051f1, LCD_ID, &lcdc_int_cfg, &LCD_drv,2);




Display presence detection

When multiple display drivers are registered in the system, determining which display driver should drive the current display requires display presence detection. The method is to first call the LCD_Init function of each display driver to initialize it, and then call the LCD_ReadID function. If the value returned by LCD_ReadID is the same as the LCD_ID value, the display is considered present and that display driver is used. Otherwise, continue calling LCD_Init and LCD_ReadID of the next display driver.

  • LCD_Init and LCD_ReadID are callback functions registered by each display driver

  • LCD_ID is a parameter passed through LCD_DRIVER_EXPORT2

  • You can directly return LCD_ID if you want to force use of this display driver. This is suitable when there is only one display driver or the display does not support ID reading.

Pixel alignment for screen refresh

Some display drivers have pixel alignment requirements for the refresh area. SiFli’s display driver framework supports setting pixel alignment (if a display has different row and column alignment requirements, use the larger value. For example, if a display requires row alignment of 2 and column alignment of 4, use 4).

The update-area pixel alignment requirements of a display driver IC are generally described in the 0x2A (start/end column) and 0x2B (start/end row) registers. For the IC shown below, both rows and columns require 2-pixel alignment:

../../_images/LCD_IC_pixel_alignment.png




Touch section

Touch (TP) framework diagram

alt text





Interface for registering a TP driver to the system

In gt911.c, the initialization function rt_tp_device_init is registered through INIT_COMPONENT_EXPORT. Then, in rt_tp_device_init, the TP driver is registered to the system through the function rt_touch_drivers_register.

static struct touch_drivers driver;

static struct touch_ops ops =
{
    read_point, //TP数据读取回调函数
    init,       //TP初始化回调函数
    deinit      //TP去初始化回调函数
};



static int rt_tp_device_init(void)
{

    driver.probe = probe;  //TP在位检测回调函数
    driver.ops = &ops;
    driver.user_data = RT_NULL;
    driver.isr_sem = rt_sem_create("gt911", 0, RT_IPC_FLAG_FIFO); //TP数据读取信号量

    rt_touch_drivers_register(&driver);  //注册到系统TP驱动框架
    return 0;

}
INIT_COMPONENT_EXPORT(rt_tp_device_init); //注册初始化函数

Backlight section

Non-self-emissive displays generally require a backlight. At present, display backlight drivers all implement an rt_device device named “lcdlight” through various methods, and it is used uniformly in the display driver callback function LCD_SetBrightness.

Two modes are currently supported:

  • PWM direct-drive backlight, where the chip directly outputs a PWM waveform to directly drive the backlight.

  • External backlight driver, where a GPIO controls an external backlight driver chip to output a PWM waveform to drive the backlight.

PWM direct-drive backlight

This device has already registered an rt_device device named “lcdlight” in drv_lcd.c. See the rt_hw_lcd_backlight_init function.

The PWM frequency used is 1 KHz by default.

It uses two macros, LCD_PWM_BACKLIGHT_INTERFACE_NAME and LCD_PWM_BACKLIGHT_CHANEL_NUM, which specify the PWM device name and channel number respectively. These two macros are generally defined in Kconfig.board.

Note: The pwm rt_device specified by LCD_PWM_BACKLIGHT_INTERFACE_NAME must be enabled in menuconfig. For example, when “pwm2” is specified, select:
alt text

Use this type of backlight by selecting the macro LCD_USING_PWM_AS_BACKLIGHT in the display module.

External backlight driver

For example, aw9364.c registers an rt_device device named “lcdlight” in the sif_aw9364_init function.

The macro LCD_BACKLIGHT_CONTROL_PIN specifies which GPIO is used to control aw9364. This macro is also defined in Kconfig.board.

Use this type of backlight by selecting the macro BL_USING_AW9364 in the display module.