Wrong routing of CEC signal or wrong schematics?

Discussion of your EDM baseboard, your add-on boards or other peripherals for your wandboard.

Wrong routing of CEC signal or wrong schematics?

Postby han_swurst » Thu Oct 10, 2013 11:27 am

Hi,
the i.MX 6Quad processor reference manual stated that for CEC signal either the KEY_ROW2 or the EIM_A25 pad is used.
But on the wandboard schematics EIM_DA2 is routet to HDMI pin 13 aka CEC (if R405 is soldered).
The mentioned pad from the reference manual KEY_ROW2 is routed to testpoint TP78 on EDM1 and pad EIM_A25 ist used for WIFI_ON.
I dont see that CEC will work when the wrong pads used for it. Or do i miss something?
Can the guys from wandboard please clarify the usage of CEC on the Wandboard.

regards
Chris
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Re: Wrong routing of CEC signal or wrong schematics?

Postby Tapani » Fri Oct 11, 2013 2:52 am

You do not miss anything. Your impression is correct. :-/
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Re: Wrong routing of CEC signal or wrong schematics?

Postby wolfgar » Sat Oct 12, 2013 12:13 am

Hi Tapani,

Thanks for confirming : I explained this one week ago on my blog (http://stephan-rafin.net/blog/2013/09/3 ... omment-496) but many people were very reluctant to believe me.
I will link to this post now.

Best regards
Stephan
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Re: Wrong routing of CEC signal or wrong schematics?

Postby `Moe` » Sat Oct 12, 2013 11:25 am

While the bad news is that you need a soldering iron, the good news is that it isn't that hard. All parts are easily accessible, it's just very fiddly. If you have never soldered SMD parts, do not attempt this. You really need to break some cheaper stuff first :)

Here's how to connect CEC to KEY_ROW2 in three easy steps:

You need 1-2cm of thin wire. Enamelled copper wire is best for this purpose, since its isolation is very thin.

First, look at the bottom (non-CPU) side of the processor board. Along the connector, search for R383. It's a bit difficult to find it, and I won't provide pictures. If you are experienced enough to solder SMD, you will find it. Unsolder it carefully, do not destroy the pads (like I sometimes do...). Keep the resistor.

Second, solder that resistor onto the empty R405 pad on the bottom of the baseboard, near the HDMI connector.

Third, solder a short piece of wire from the connector-side pad of R383 to TP78. TP78 is really difficult to find, because the labels are far away (marked "H"). It is about 1cm away from R383.

Et voilá.

Explanation:

R383 is a 0-Ohm resistor that is part of the CEC-R405-EIM_DA2 routing. It must be removed if R405 is fitted, because it connects a pull-down resistor to the line (R17). The sweet thing about this is that you don't need a fragile board-to-board wire. With R405 fitted, the CEC signal arrives at R383, and with R383 removed, you have an easily accessible solder pad that's near TP78.

I have measured signals, and it works. I get some sort of digital traffic when my TV is turned on. I can influence the line level through corresponding registers (when HDMI is unplugged, of course). Unfortunately, I did not yet get successful control, I guess my TV is to blame.

If anyone knows anything about CEC on an elderly LG plasma TV, any input is appreciated. It says "no simplink device" when I press the corresponding button on the remote.
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Re: Wrong routing of CEC signal or wrong schematics?

Postby wolfgar » Sat Oct 12, 2013 1:24 pm

Hi Moe

Thanks a lot for this tutorial to fix the CEC hw design.
Regarding your issue faced to your TV : How do you test ?
Do you use my image with modified kernel + modified libCEC + CEC ready XBMC ?
If so, I can probably help you : Please send to me your xbmc.log and let's continue this chat on xbmc thread or by mail ... ( As it is no longer a wandboard related discussion)
Odds are high that the CEC signal is now OK but that at some stage your TV issues a vendor specific command which is not understood and stops speaking to your board...

Best regards
Stephan
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Re: Wrong routing of CEC signal or wrong schematics?

Postby `Moe` » Sat Oct 12, 2013 8:53 pm

Thanks for the help, wolfgar. It now works (modulo LG's CEC braindeadness).
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Re: Wrong routing of CEC signal or wrong schematics?

Postby rbraken » Fri Oct 18, 2013 2:11 pm

Just a confirmation:

I did the hardware modification as described by Moe on my wbquad.
I applied two fixes to my kernel (both from Wolfgar) to board-wand.c (IOMUX configuration)
and to mxc_hdmi-cec.c (cec driver).
I also used Wolfgar's patched libcec.

Now cec-client is giving me a lot of info :)

Greetings Rene
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