DSI Video Mode (RGB888) with ST7703 on STM32U5G9NJ

[PAV]

 

• uC – STM32U5G9NJH6Q

• Display – 720 × 720 (ST7703 panel)

• Display controller – ST7703

• MIPI lanes – 2 lanes

• DSI Host Mode – Video Mode (DSI_VID_MODE_BURST)

• Pixel format – RGB888

Problem / Symptoms

1. After the initial display setup (LP mode initialization sequence), the backlight turns ON, but no image is displayed on the LCD.

2. I have verified that the MIPI DSI clock and data line waveforms are present and active on the scope — both lanes appear to be toggling correctly.

3. Despite proper DSI signal activity, the panel remains blank (black screen), and there is no visible frame output from TouchGFX.

What I have verified/working

• I can communicate with the display over DSI and run the initialization sequence (LP command mode) — panel responds, backlight comes on.

• LTDC timings & basic parameters match the panel spec and st7703.c values (see below).

• PHY frequency configured around panel-recommended range (450–510 MHz / VCO ~800 MHz–1 GHz).

• TouchGFX / display driver configured to disp_ltdc. dma_2d and gpu2d acceleration enabled. vsync source set to LTDC.

• Backlight PWM and reset GPIO working.

My LTDC configuration (current)

• Resolution: 720 × 720 (active) — matches ST7703.

• Pixel Format: RGB888.

• Porch & sync (approx / set to values close to st7703.c):

  • HSync = 6, HBP ≈ 51, HFP ≈ 51 (I used HSync=6, HBP=3 earlier while calculating HorizontalLine = 1452 — verified active + porches match).

  • VSync = 2–3, VBP ≈ 12, VFP ≈ 12–15.

• Layers: 1. Buffering strategy: Single at present (I can switch to double).

DSI Host settings

• Mode: DSI_VID_MODE_BURST (continuous video).

• Lanes: DSI_TWO_DATA_LANES.

• LP command mode: enabled (to send DCS commands like DISPLAY ON).

• PHY frequency: set to panel-recommended range.

• LP mode enabled for porch/sync intervals (low power during those phases).

• HorizontalLine computed appropriately for active + porches + sync (e.g. ~1452 for current timing).

TouchGFX

• Display interface: disp_ltdc.

• Buffering: Single (considering Double).

• Hardware accel: dma_2d, gpu2d_enabled.

• VSYNC source: vsync_ltdc.

Backlight / Reset

• Backlight PWM: TIM15_CH2 on PB15 — works.

• LCD_RESET: PD4 — matches st7703.c.

 

Has anyone successfully run TouchGFX with DSI Video Mode (burst) on an ST7703 panel (RGB888 / 2-lane)? If yes, could you share example project or configuration highlights?