Summary of Issues Related to RGB Interface Screen
This document mainly summarizes the common problems in the development process of the RGB interface screen and provides corresponding solutions.
Solution to Screen Drift Issue
Effect diagram of screen drift
Root cause of drift: The “drift” is essentially that after the GDMA interrupts the transmission stream (FIFO under-run), the LCD controller continues to take pixels from the wrong address, thus displaying the subsequent lines as the first few lines, and the entire image produces a line-by-line shift. It is a macro manifestation of GDMA → LCD FIFO underflow + FIFO pointer misalignment.
Solution:
BounceBuffer ≥ 20 lines (not too large, so as not to affect the execution of other interrupts), to ensure that ISR refill has enough VBlank time window
esp_lcd_rgb_panel_config_t panel_config = { .data_width = EXAMPLE_DATA_BUS_WIDTH, .dma_burst_size = 64, .num_fbs = EXAMPLE_LCD_NUM_FB, .bounce_buffer_size_px = 20 * EXAMPLE_LCD_H_RES, .clk_src = LCD_CLK_SRC_DEFAULT, .disp_gpio_num = EXAMPLE_PIN_NUM_DISP_EN, .pclk_gpio_num = EXAMPLE_PIN_NUM_PCLK, .vsync_gpio_num = EXAMPLE_PIN_NUM_VSYNC, .hsync_gpio_num = EXAMPLE_PIN_NUM_HSYNC, .de_gpio_num = EXAMPLE_PIN_NUM_DE, .data_gpio_nums = { ... }, .timings = { .pclk_hz = EXAMPLE_LCD_PIXEL_CLOCK_HZ, .h_res = EXAMPLE_LCD_H_RES, .v_res = EXAMPLE_LCD_V_RES, .hsync_back_porch = EXAMPLE_LCD_HBP, .hsync_front_porch = EXAMPLE_LCD_HFP, .hsync_pulse_width = EXAMPLE_LCD_HSYNC, .vsync_back_porch = EXAMPLE_LCD_VBP, .vsync_front_porch = EXAMPLE_LCD_VFP, .vsync_pulse_width = EXAMPLE_LCD_VSYNC, .flags = { .pclk_active_neg = true, }, }, .flags.fb_in_psram = true, // allocate frame buffer in PSRAM };Open XIP configuration to reduce long-term blocking, improve interrupt real-time performance, and thus reduce RGB FIFO underflow and drift.
Support for external PSRAM ---> PSRAM config ---> [*] Enable Executable in place from (XiP) from PSRAM feature (READ HELP) - LVGL uses Direct Mode or reduces the refresh rate to minimize PSRAM bandwidth usage.[*] Avoid tearing effect Select Avoid Tearing Mode (Mode3: LCD double-buffer & LVGL direct-mode) ---> Select rotation (Rotation 0) --->
Insufficient GPIO
The RGB interface will occupy a large number of GPIOs. If there is not enough IO, consider using a GPIO expansion chip to expand the SPI line, or consider multiplexing the data line with the SPI line.
Hardware reference: SCH_ESP32-S3-LCD-Ev-Board-MB_V1.5_20231009.pdf