Linux/AM5708: Dual LVDS with DS90CF387 has image issues

Hi,

Please post which Linux version you use.

Hi Biser, this is my Kernel version:

 Linux version 4.14.54-g976d7a5851

I'm using TI SDK 04.02.00.09

 I notice any color that uses green has issues (check the above table against the original photos attached).

Still looking for tips on figuring this issue out. I checked the cable / schematics and they look ok.

Hi Lee,

I am from the AM57x team. I am not an expert on the DS90CF387 chip, so you will need to explain your problem in more detail to figure out if this is issue with AM5708 usage or DS90CF387 device.

Please explain the source of RGB1 and RGB2 signals? Are they being sourced from twp different VOUTs? What is this bridge chip expecting as input signals from the AM5708 device (synchronized  RGB1 and RGB2 inputs??) ?  Have you tested the signals are indeed received as expected?  How are you consuming these signals to drive your dual display?

Hi Manisha, please check my schematic:

Those LCD_RED* / LCD_GREEN* / LCD_BLUE* pins go straight into the DS90C387. So I am using VOUT3 only.

Also, I'm not using dual display (as in 2 different outputs). I'm using dual LVDS to drive a single LCD panel at FHD resolution. Dual LVDS (and not single LVDS) is required for FHD.

I believe the connection between the SoC and DS90C387 is correct. When I drive a smaller panel (1280x1024), using single LVDS, there is no color issue.

Let me reiterate, DS90C387 is responsible for outputting single and dual LVDS outputs. Between the SoC and DS90C387, it is 24bit RGB.

Thanks for the explanation. The fact that you are able to drive the display correctly for smaller resolution, it makes me feel that this may be a signal integrity issue.

I am from software team. Let me route this ticket to our hardware applications engineer.

Regards,
Manisha

Adam,

Please show a schematic showing the connections between the DS90CF387 and the LCD panel in both the functional and non-functional cases.  That is the cable type and length and what type of connectors are you using?

What pixel clock rates are you using on the VOUT3 in the various use modes that you are using?  Please provide scope captures showing that the critical timing on the VOUT3 24-bit RGB bus is met at the fastest speed.  Can you get the dual LVDS mode to work at a lower resolution or slower update rate?

Tom

Hi Tom, please see attached for connections between DS90CF387 and LCD panel for single LVDS and dual LVDS. Note that the dual LVDS case needs modification to the schematic to enable LVDS mode.

For single LVDS, clock is 74.4mghz. And for dual LVDS, it is 148.8 mghz.

I will try to get you the scope capture. Will try lowering the clock speed as well.

Adam,

Have you been able to run these tests?  Alternately, have you found a solution to your problem?  Please let us know.

Tom

Adam,

You stated: "The output format from DS90c387 doesn't match with the input format of my display".  The DS90C387 is a standard serializer device that converts parallel RGB data to serial streams that are OpenLDI compliant.  I do not see how changes in the RGB data coming from the AM5708 can fix your serial data format issue.  It appears to me that you either need to choose a different serializer that is compatible to your display OR choose a display panel that is compatible to the OpenLDI serial interface which is available from the DS90C387 serializer.

Previously you mentioned that the DS90C387 and your display panel communicated correctly at lower resolutions.  Can you explain this?

Tom

Hi Tom, thanks for the respnse. I can't find any mention of OpenLDI from the display datasheet. So I should assume it's not.
Previously I stated the colors look good as long as I set my display manager (Weston) to use RGB565, not full RGB888.

Adam,

What are you planning to do to resolve your display compatibility problem?

Tom