Beaglebone black audio when using yocto build (not registered with alsa ) vs default eMMC build

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Oluwokay Victor Johns

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Feb 22, 2015, 2:33:03 AM2/22/15
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All, 
  I am trying to get audio working on my BBB using a yocto derived build running on an SD card. A couple of notes
1) When I plug in a micro HDMI cable and use the default internal flash build, the HDMI is detected and registed with ALSA. When I use the yocto derived build. The HDMI is not detected 
2) I have gone thru the TI WIkis and enabled  ( what I believe are) the necessary settings in the kernel in order to get the HDMI audio transmitter working. I have followed the direction here  http://processors.wiki.ti.com/index.php/Sitara_Linux_SDK_Audio_BeagleBoneBlack_HDMI 
and also the subpage about enabling the DRM 
3) The linux-yocto kernel image being generated is based off of 3.14.29. I believe I have the correct dtb file as pointed out in the above link but ...
So at this point, since the HDMI audio is not being registered with alsa,  I am kind of at a loss as to what to do next. 
Running i2cdetect on the currently running image gives : (i2cdetect -r -y 0 ) 

 0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: UU -- -- -- -- -- -- --  

and on the internal flash image gives 

    0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: UU -- -- -- -- -- -- --  

And, when I type aplay -l on the internal image, the card is detected. 
cat /sys/bus/i2c/devices/0-0070/name on both images gives tda998x (HDMI transmitter IC ??) so it looks like in both cases the i2c device is there
One last note is that currently in order to make sure it's not a module dependency issue, I am building this functionality into the kernel ( I am not sure if this makes a difference or not) 

I was wondering if anyone here could provide some info on some steps I could take to debug this issue (and also gain some understanding along the way).

Thanks Much 

Victor 
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