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AM35x RGB888 LCD not working

Krunal Patil
Genius 3120 points
Other Parts Discussed in Thread: AM3505, AM3517

Hello,

I have AM3505 based custom board on which I am using an touchscreen LCD (480x272, RGB888). I am in process of getting LCD display. To achieve this I have modified existing "Sharp LCD driver" to support RGB888 format and LCD timings (pixel clock, hfp, hbp, hsw, vfp, vbp, vsw) that are provided in our LCD datasheet. Other than this I verified / changed following parameters:

  1. DISPC_CONTROL to 24 Bit data interface
  2. DISPC_GFX_ATTRIBUTES24 bit data interface
  3. DISPC_TIMING_H and DISPC_TIMING_V
  4. DISPC_SIZE_LCD
  5. DISPC_DIVISOR

After doing all the settings I modified TI sample application saFbdevDisplayPan (which uses two buffer for pan display) to support RGB24 and executed that application. Image: 1 is that out that we are trying to display on LCD and Image: 2 is the actual data that is displayed on the LCD.

Image: 1 Actual data trying to display

Image: 2 Data displayed on LCD

Observations:

  1. Application works well on the AM3517 EVM. and display output as expected in image: 1
  2. Output displayed on custom board (i.e Image: 2), Data is displayed as shown in figure and not in complete screen. As this is pan display application the color bars are scrolling from top to down. The observation here is the bottom most color is displayed in the whole screen as shown by marker.
  3. When I tried to display a QT GUI on the custom board it was not displayed , whereas the same application is displayed proper QT GUI on EVM board.
  4. When I tried to play with the LCD timing using sysfs interface, I am able to shift the color bar to right side but still the QT application does not work in that case.
  5. Boot logo: I also tried to display kernel boot logo and that was also not displayed. Kernel displays white screen instead of boot logo.

Hardware Interface:

The LCD interface to DSS is as given in the AM3505 userguide page: 1201.

We have already followed following link:

http://processors.wiki.ti.com/index.php/Display_Subsystem                     
http://processors.wiki.ti.com/index.php/LCD_connectivity                      
http://processors.wiki.ti.com/index.php/Adding_new_DVI_resolutions            
http://processors.wiki.ti.com/index.php/UserGuideDisplayDrivers_PSP_03.00.00.05

My end goal is to display boot logo and QT GUI application on touch screen LCD.

Can anyone please suggest some hint to debug this issue? I am not able to understand what is happening inside the display subsystem. Are there any settings missing?

Looking forward to your support.

--
Thanks & Regards,
Krunal Patil