vga output from am335x interfaced with 8200

Can you look at the Am335 digital outputs to make sure they are all toggling correctly? Check V-sync, H-sync and each of the data lines.

Can you check the THS8200 H & V sync outputs to make sure they are toggling?

Does your monitor indicate there is an image but it happens to be black, or does it not detect an image at all? This is often checked in the monitor menu somewhere where it will report the currently detected video resolution. The monitor may say "no signal' or 'signal out of range' or some similar message.

BR,

Steve

OK, so I think you have found the issue :)

How are you configuring the THS8200? Is it slave or master timing?

Are the H & v outputs from the processor correct?

Are you using discrete syncs or embedded syncs between the processor and the THS8200?

Use the configuration setup files from here to configure the THS8200 correctly for your specific configuration...

http://www.ti.com/product/ths8200

The first and most critical thing to get is the monitor to detect the correct output resolution from the THS8200, then we can work on getting the image displayed correctly from the frame buffer.

BR,

Steve

Hi Steve,

THS8200 is configured as slave timing. 

I had checked H & V outputs from processor, and those are correct. I'm using discrete syncs between processor and ths8200.

I configured the register according to the setup files provided.

The monitor detects the o/p resolution from the ths8200, but still the screen is blank.

Regards,

Subhendu 

Hello Steve,

Thanks for your suggestions. Finally I'm able to show the video o/p to the monitor which is 640x480@64Hz and the lcd monitor now able to autodetect the vga mode. Linux logo is displaying and I'm able to display some low resolution still images (320x240) using fbv.

But, now I'm facing a new problem, when I'm trying to display greater resolution images; the screen goes blank.

When I'm running fbtest the display goes blank and power down mode momentarily. So, finally I'm able to display some low resolution still images and can't able to run any videos.

What might be the problem ?

Regards,

Subhendu

To be honest there are a million things that could be wrong.

What you need to do is try to debug each section of the video path rather than the entire thing all at once.

I suggest first checking that the AM335x output timings are correct. Focus on the h-sync, v-sync and AVID signals (don't worry about video data yet). If these are correct then check the THS8200 output H & V to make sure that they are also correct. If the AM335x is correct but the THS8200 timings are not then it is a THS8200 configuration issue

If the THS8200 output timings look correct then does the monitor correctly detect the video mode (again, do not worry about the actual displayed image, only whether the timings are detected correctly). If the timings are detected correctly, but the displayed image is not correct then start looking at the frame buffer configuration etc...

If the timings look correct then try enabling the AM335x output test pattern generator. If this displays correctly but the frame buffer image does not then it tells you everything from the DSS onwards is OK. If no image is displayed then the DSS and/or THS8200 are not configured correctly.

Basically, break the problem down in to manageable chunks and debug each stage in the path starting at one end and moving up the path.

BR,

Steve

Hi Steve,

Finally I'm able to display VGA resolution output with a minor glitch. Every application is running properly in windowed mode, but when it is in full screen mode the images or videos are going dim and partially or totally blank.

Later, I found that on the right hand side of the active video region, around 1/2 inch vertical region is the culprit.

Here I am attaching one image of the lcd screen where you can see the highlighted mouse cursor is distorted when it is touching that particular region. I tried to resolve the problem by changing frame buffer driver parameters, but still it exists. Can you tell me what might be going wrong here ?

Thanks in advance.

Regards,

Subhendu

This looks like an AM mis-configuration, possibly in the frame buffer driver/configuration.

This could be many things still, but I don't think the THS is the issue.

When you say "windowed mode is OK" do you mean that even if you move the window completely to the right hand edge into the region which is currently corrupt that it displays OK? Can you ever display something correctly in this right hand region? What I am trying to determine is where in the rendering path the fault is.

Can you display a mainly white display then capture a line of active video on an oscilloscope, showing h-sync and each or red, green and blue? One color will be OK if you can't capture all color channels.

Make sure that the horizontal front and back porches are correct for the resolution you are trying to display.

Brightness variations in analog video are most often caused by the active video encroaching in to the sync region.

Do you get exactly the same results on different monitors? Sometimes different behavior can help determine the root cause.

BR,

Steve