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40A856 optical output ?

Posted: Sat Jan 11, 2014 3:06 pm
by marcjero

happy new year all. :D

I wonder if it's possible to pass ac3 and/or dts from hdmi device to the optical ouput ?
I know that some TV models allows that, other don't...

I looked in service menu and didn' find anything related to optical ouput.

What is your feedback about A-series please ?

Re: 40A856 optical output ?

Posted: Wed Jan 22, 2014 11:39 am
by marcjero
answer : no dolby digital or DTS passthrought is possible. I tried to force the HDMI EDID but TV only forwards PCM 2 channel to spdif.
I suppose this could be fixed in the firmware.

update : I check with another hdmi cable and an xbox and had the same result

Do you think it is an hardware restriction ?

Re: 40A856 optical output ?

Posted: Sun Jan 26, 2014 9:24 am
by tom_van
STi710x chip probably can forward DTS from HDMI to S/PDIF. Unfortunately HDMI inputs and S/PDIF out are handled by MTK8226 (secondary CPU).
I don't have a datasheet for this chip and I don't want to disassemble another huge firmware.

Re: 40A856 optical output ?

Posted: Sun Jan 26, 2014 2:13 pm
by marcjero
Hi Tom,

I understand.
I looked deeper in the service menu and found a MFI section in the advanced settings. MFI sounds like Mediatek Firmware. Inside this section there is a strange R_FULLBYPASS setting.
Do you think it's safe to play with this setting ?

Anyway I'm ready to investigate more on this. Is the MTK firmware included in Samsung firmware ?

Re: 40A856 optical output ?

Posted: Sat Feb 01, 2014 12:27 am
by marcjero

I found that sound (incl from hdmi) is processed first throught a mt8291 chip. I didn't find its datasheet. Anyway this chip is described as a stereo chip so I guess it does just ignore any mutichannel input. So I suppose it's really a hardware limitation as this chip doesn't use any firmware (afaik) This explains why ac3 is working from tuner but not from hdmi. No hack is possible here I'm afraid.

Re: 40A856 optical output ?

Posted: Sat Feb 01, 2014 12:15 pm
by tom_van
I don't think that HDMI input can go to MT8291.

Here is some description of MT8291 from other TV service manual:
The MT8291 is a highly integrated stereo audio CODEC. The MT8291 performs stereo
analog-to-digital and two digital-to-analog conversions with single-ended analog voltage input
and output. It?s up to 24-bit serial values at sample rates up to 192 kHz. A 7:1 stereo input
multiplexer and an automatic level control are included.
AFAIK HDMI goes to SIL9185 (HDMI PHY, mux and EDID) and then to MT8226. So the passthrough might be possible in MT8226 firmware.
Try to find if such hack exists for TV platform where is used only MT8226 (AMBER, PEARL ??) and not STi710x. Even if such hack exists, MT8226 firmware
for A7/8/9 is substantially different.

Re: 40A856 optical output ?

Posted: Sat Feb 01, 2014 6:40 pm
by marcjero
Yes you are probably right as I don't see why HDMI audio would need to go throught a DAC.

Do you know if it's possible to read the hdmi data from STi710x ?
Writing to spdif is possible because wiselink does that. If it's possible to read hdmi in could be possible to run a passthrought daemon outside of 8226.

I looked in the device drivers and modules and didn't find anything interesting so far.

Re: 40A856 optical output ?

Posted: Fri Feb 14, 2014 10:03 pm
by tom_van
The only schematics I have is a block diagram and it shows that HDMI goes just to MT8226. And data sheet of STi710x does not describe any HDMI input. So the only way is inside MK8226.