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ADV7171 Data Issues?

Question asked by Dr.Lightning on Mar 6, 2011
Latest reply on Mar 7, 2011 by DaveD

At http://ez.analog.com/thread/6306?tstart=0 I've describe "ADV7171 video output sync issues".

At http://ez.analog.com/thread/6307 I've described "ADV7171 fuzzy output issue".

 

Now I'm wondering if it's all just a DATA issue.

 

I upgraded my driver in the Linux kernel to alternate between ADV7171-generated color bars and data-to-output, each time I run my application.  When the ADV7171-generatedcolor bars run, I get a great stable display.  The white bar on the left is white.  The black bar on the right is black.  Everything looks like http://aaronstarmer.com/blog/wp-content/uploads/2010/06/EBU_ColorBars-768x576.png.  The scope trace is OK.  (more on this far below)  All this suggests to me that my analog electronics outside of the ADV7171 are fine.

 

I also upgraded my DM4647T test program to fill the image with color bars, each bar YUV color coming from a table in the program.  When I run the program, which sends data via Linux O/S and V4L2 drivers to the ADV7171, I get a mess.  I changed my table to make a collection of green, gray, and magenta bars, and the output looks great. 

 

Whenever I change the first bar to white, YUV=(255,128,128), I get vertical & horizontal sync issues (V: horizontal black lines; H:whole image right shifted).  And on the scope looking at one video line, the time where I should have a sync+backporch+colorburst (ref http://en.wikipedia.org/wiki/Analog_television#Structure_of_a_video_signal), I have TWO such in a row.  It's as if this YUV combination is causing the ADV7171 to sync again, sync again [humorous studder].  NOTE I'm running in "Mode 0 (CCIR-656): Slave Option" right now.

 

When I change the first bar to YUV=(185,128,128), the sync sync problems go away, but the colors are bogus.  The YUV=(185,128,128) bar should be just a less bright white, but instead it looks like a light magenta (akin to RGB=(255,196,255)).  The other colors are all wrong, too.  The next bar, yellow (or mustard to my eyes, i think it's supposed to correspond to RGB=(196,196,0)) looks like a slightly darker magenta.  The cyan bar is a bluer magenta.  the green bar looks more like dark mustard.  The magenta bar looks the same as the white bar (akin to RGB=(255,196,255)).  The red bar is a red-orange.  The blue bar is bright-light-blue (akin to RGB=128,196,255).  And the black bar is black but full of white noise (reminiscent of an analog oversaturation problem where white has black noise, but this is black with lots of white noise.)  NOTE ALSO the scope trace for this dingy white is not a flat line (with 27MHz noise) Y value, but a has a fully modulated chroma signal.  So it really is being output as a light magenta color.

 

All of this makes me wonder about my data.  I have a reliable RGB-YUV converter that I developed while doing some codec work last year.  And I have a reliable RGB-YCbCr converter that I developed while working the the DM6467T EVM (evaluation module) and Hi-Def video.  Even if my conversions were off slightly, it wouldn't cause color troubles this bad.  And it certainly wouldn't cause sync problems merely because of color.

 

Please help me get to the bottom of this!

 

 

COLOR BAR EXAMPLES for you to see in this forum
This background color is similar to my blue bar, but the blue bar is a little more "brilliant"

 

 

COLOR BAR EXAMPLES for you to see in this forum
This is RGB=(255,196,255) and it looks similar to what my dingy white bar looks like.  Dingy white is YUV=(185,128,128)

 

 

Thanks very much,

Helmut

 

 

About the scope trace, my old 20MHz analog scope doesn't show the 27MHz noise at all.  It doesn't even show the 13.5Mhz version of the noise, either.  While my 60MHz digital scope does show the noise, which has a substantial 13.5MHz component, even when I turn on 20MHz bandwidth limit.  So I think a good portion of the noise is just my test environment and my scope, not the actual board signal.  The noise is coming from the board into the scope, perhaps through the 120V wall supply, but not necessarily from the measured signal itself.  The analog scope trace looks just like http://t0.gstatic.com/images?q=tbn:ANd9GcT4-8E4fn8GHdLztYx0H_I65yG0w64n8rvW_9Tg2hpeyCTD-WuM&t=1, including flat Y signal without chroma.

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