Dump everything you know about HDMI eARC here

[morethinkingcapacityneede]

Awesome overview, thanks for putting it together and sharing. And please keep us posted on your progress with the nxp eval board, the ones I was aware of from lattice were several hundred euros if I remember correctly.

Thanks! For sure, I’ll report back

 

[morethinkingcapacityneede]

Woah, looking at the datasheet for the nxp i.MX 8M Plus (I had to make an account to access it so I won't screenshot or quote it directly) on page 6159 it certainly seems like this handles eARC input, I think I may pick one up myself! Unfortunately still a bit price e.g. $126 on mouser but still a fraction of the cost of the miniDSP and seems like a fun platform for learning and science. I'd still rather be able to just do the eARC with e.g. one of those Sil9437, but I suppose I'll just have to abandon that dream.

Yeah, I think the SoC does it all. It has a couple of dedicated DSP cores, but you’d have to get familiar with their libraries. For the HDMI spec, it is available without a paywall, if you do a web search

edit:
Also, worth saying that the NXP documentation is solid and professional, e.g. including detailed instructions on building the linux images. I guess that's because they are quite a bit bigger than the other more "diy orientated" SBCs makers, which still do have useful documentation, and sophisticated build systems.

 

[morethinkingcapacityneede]

Wow, thank you for such a great and detailed response!

My idea was to essentially build my own miniDSP flex HT, just for the fun of it/for learning. I like the idea of tinkering with the PCM signal and communicating with the host device via CEC for like volume control and stuff. I was thinking of using something like an ADAU1797A do do the dsp once I get the PCM out of the HDMI, but really all this is new to me so . It even seems like one could use e.g. SSM-2125 to decode the dolby surround stream if they wanted, which may also be fun to tinker with.

From the research I've done, the CEC should be relatively straightforward to "bit bang" as it's a relatively slow communication on a single wire. the ARC/eARC stuff is a different story, and while I think it'd be fun to try to implement those too the price of entry for the HDMI spec is just too high.

I'll certainly take a look at the SMCs you've listed, and I'm interested to hear your experience with the NXP

No problem at all. Unfortunately, I have found that HDMI related electronics are often not compatible with the diy ethos. I would have bought a miniDSP Flex HT if it just had auto source switching

 

[Philbo King]

Hi,
As a tangent from another project i recently became interested about HDMI eARC, to the point that I went and read everything about it I could find in the internet. It took me about 30 minutes.
Not satisfied, i bought from Aliexpress the cheapest eARC audio extractor that I could find. It is one of those boxes that takes eARC and outputs audio over HDMI. The insides of the device turned out to be more interesting than I initially thought for the price:
The device has two ITE ICs. The smaller one, more modern and capable, receives the eARC signal and transfers the audio via multichannel i2s (4 data lines+clocks) to the bigger IC, that generates the "audio over HDMI" output. Fortunately, there is a short datasheet available for the output IC (IT66121FN) that confirms that those pins that receive the data from the first IC are indeed i2s inputs. ( https://www.infinite-electronic.pt/datasheet/e0-103030034.pdf )

View attachment 379282

Here i need to stop and say that both ICs are controlled by a MCU and it is well beyond my capabilities and interest to try to figure out what is going on there and how the thing works. I can imagine there are EDID handshakes etc. happening when you connect sources and sinks. Just check the amount of exposed headers and test points, the extractor is more complex than it seems.

Anyways, what called my attention is that both ICs are capable of a few audio formats, including DTS-HD and Dolby TrueHD in between others. And seems that it is possible to transmit those formats, encoded, through the i2s data lines.
Now my question or suggestion is. Having access to those i2s data lines, is there a way to capture and decode the audio to LPCM? Does it make it any easier to capture the data in this format vs embedded in the HDMI video signal? has this been done before?

There is a bit of discussion in the Analog Devices forum, in between other posts, here:

How HBR audio bitstream embedded to I2S output interface in parallel mode when audio input source is Dolby TrueHD and DTS-HD Master Audio? - Q&A - Video - EngineerZone

Dir Sir. We have questions about how ADV7622 put HBR audio bitstream to I2S output interface in paralle mode(4 data lines). Is there any format diff. output from

ez.analog.com

Some pretty good info here:

HDMI - Wikipedia

en.wikipedia.org

 

[morethinkingcapacityneede]

Some pretty good info here:

HDMI - Wikipedia

en.wikipedia.org

I forgot to mention I came across an eARC patent belonging to Lattice: https://patents.google.com/patent/US20180288106A1/en?oq=US+2018/0288106+A1. It has some good info about the link negotiation mechanism. (I think this implies Lattice came up / were heavily involved in eARC)

 

[morethinkingcapacityneede]

Thanks! For sure, I’ll report back

Received the NXP FRDM i.MX 8MP today, very nice dev. board, well packaged. Has Linux pre-loaded in the eMMC, and booted OK (does not work with Apple laptop chargers, I've seen this before with other SBCs as well).

Everything worked out of the box. I managed to initiate ARC Tx from the TV, and record the audio to a .wav file

 

[stigger]

Sounds like a good start! Is there any way to physically hook up to the clock signal that's coming from HDMI? With the external HDMI extractor I was able to drive DAC through S/PDIF and therefore run CamillaDSP without rate adjusting.

 

[morethinkingcapacityneede]

No idea with regards to routing the HDMI clock anywhere, maybe it's possible. The SoC supports SPDIF in and out (see screenshot), so maybe something can be done with that.

 

[morethinkingcapacityneede]

In this example for a slightly different board, eARC is routed to the headphone output: https://docs.nxp.com/bundle/UG10163/page/topics/hdmi_earc_support.html