"RT-Thread Device Driver Development Guide" reading notes - LCD device driver

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"RT-Thread Device Driver Development Guide" reading notes - LCD device driver [Copy link]

# Preface Nowadays, screens are the main body of human-computer interaction, and their status in embedded devices is getting higher and higher. In various fields such as instruments and tools, home appliances, motorcycles, retail, etc., if there is no beautiful UI, the high-end of the device cannot be reflected. RT-Thread abstracts the basic functions of LCD and develops an LCD device driver framework to facilitate application development and develop graphics applications that are decoupled from specific hardware. At present, the LCD device driver framework also supports GUI engines commonly used in the embedded industry, such as LVGL, TouchGFX, etc. **Table of Contents** [TOC] # LCD hierarchical structure```flow op1=>operation: application op2=>operation: I/O device framework op3=>operation: LCD device driver framework op4=>operation: LCD device driver op5=>operation: hardware: LTDC/MIPI/SPI/... op1->op2->op3->op4->op5 ``` - The I/O device driver framework layer mainly provides a unified operation interface for the device framework, including rt_device_read/write/open, etc. - The LCD device driver framework is an abstraction of the basic functions of LCD. It is a general software layer that is independent of the hardware platform and includes the type definition and specific operation methods of LCD devices, such as rt_device_graphic_info/ops. - The LCD device driver only needs to implement the LCD device operation method, rt_device_ops, to update the buffer of the hardware controller in the control interface to realize screen drawing, and rt_device_graphic_ops, which provides operation methods for controlling hardware drawing such as drawing points and lines. - The hardware layer is an adaptation of the driver communication protocol to realize the communication between the MCU and the screen controller. # LCD Implementation The development board used in the example in this article is the HMI Board development board. First, define an LCD device object```c struct drv_lcd_device { struct rt_device parent; struct rt_device_graphic_info lcd_info; void *framebuffer; //... other properties can be added}; struct drv_lcd_device _lcd; ``` LCD device registration```c int rt_hw_lcd_init(void) { struct rt_device *device = &_lcd.parent; //...some code omitted/* draw graphics device information*/ _lcd.lcd_info.height = LCD_HEIGHT; _lcd.lcd_info.width = LCD_WIDTH; _lcd.lcd_info.bits_per_pixel = LCD_BITS_PER_PIXEL; _lcd.lcd_info.pixel_format = LCD_PIXEL_FORMAT; _lcd.lcd_info.framebuffer = (uint8_t *)&fb_background[0]; device->type = RT_Device_Class_Graphic; #ifdef RT_USING_DEVICE_OPS device->ops = &lcd_ops; #else device->init = ra_lcd_init; device->control = ra_lcd_control; #endif /* Register LCD device*/ rt_device_register(device, "lcd", RT_DEVICE_FLAG_RDWR); // Initialize LCD controller ra_lcd_init(device); ra_bsp_lcd_set_display_buffer(1); return result; } ``` The control interface implementation includes update commands, power control, device information acquisition, etc., which can be implemented according to actual conditions. ```c static rt_err_t ra_lcd_control(rt_device_t device, int cmd, void *args) { struct drv_lcd_device *lcd = (struct drv_lcd_device *)device; switch (cmd) { case RTGRAPHIC_CTRL_RECT_UPDATE: { struct rt_device_rect_info *info = (struct rt_device_rect_info *)args; ( void)info; /* nothing, right now */ rt_kprintf("update screen...\n"); } break; case RTGRAPHIC_CTRL_POWERON: rt_pin_write(LCD_BL_PIN, PIN_HIGH); break; case RTGRAPHIC_CTRL_POWEROFF: rt_pin_write(LCD_BL_PIN, PIN_LOW); break; case RTGRAPHIC_CTRL_GET_INFO: { struct rt_device_graphic_info *info = (struct rt_device_graphic_info *)args; RT_ASSERT(info != RT_NULL); info->pixel_format = lcd->lcd_info.pixel_format; info->bits_per_pixel = 16; info->width = lcd->lcd_info.width; info->height = lcd->lcd_info.height; info ->framebuffer = lcd->lcd_info.framebuffer; } break; case RTGRAPHIC_CTRL_SET_MODE:break; } return RT_EOK; } ``` The main function is to control the interface, and the rest is to initialize the controller. When using the LCD device, write data to the framebuffer. If the framebuffer is a cache, then write the data to the screen through the framebuffer. If the framebuffer is a screen memory mapping, then there is no need to write data. # In summary, the structure of the LCD device is relatively simple. It mainly provides LCD information to the upper layer, such as width, height, pixel length, frame buffer address, etc. Then the interface for reading/writing data to the LCD hardware is completed, and the read interface is optional. The remaining main functions are implemented in the graphics library. # Refer to the LCD device driver related content in Chapter 14 of this book.

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