[Arm-netbook] HDMI v1.4 Audio Return and Ethernet channels

[Andrew Bolin]

so *i'm* not quotes considering it quotes - if it's there and there's
a linux kernel module it's there, people can compile it and use it.
l.

Can't use it if the pin has no connection to the CPU!

In the last screenshots I saw (
Loading Image... ), pin 2 HEAC+
(ethernet/ARC) is not connected to anything. Pin 1 (HEAC- & HPD) does go
somewhere, but it's of no use for these functions by itself.

CEC does seem to be routed and is mentioned on the A20 info page.

No SBC that I've seen actually uses these functions (unfortunately).

- Andrew.
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[Richard Wilbur]

On Mon, Jul 31, 2017 at 11:13 PM, Luke Kenneth Casson Leighton

CEC etc i believe is supported i can't remember the details, it's
covered by the processor and is somewhere in the datasheet. certainly
i know there's an hdmi audio kernel module for sound playback in the
sunxi-3.4 kernel.

Sorry, I explain things well enough. Sound playback normally refers
to sound output from the kernel to D/A, amplifier, and speakers. Same
direction as video playback: from computer to monitor.

CEC: Consumer Electronics Control
Allows devices to pass control information around. Say you have a
remote control for your television that has "Play" and "Pause" buttons
on it, for instance. Through CEC the commands could be sent from your
television to the EOMA68-A20 card via the HDMI cable and software
there could respond appropriately to the events.

ARC: Audio Return Channel
The Audio Return Channel supports sending digital multi-channel sound
upstream (for input to the computer). This would allow recording,
mixing, special effects, etc.

so *i'm* not quotes considering it quotes - if it's there and there's
a linux kernel module it's there, people can compile it and use it.

From the sound of things, CEC was there from the beginning and ARC is
new in v1.4 but doesn't require circuit changes on the HDMI
transmitter PCB to accommodate. ARC does require support in the HDMI
block/subsystem of the SoC.

On the other hand, if we plan to support HEC (HDMI Ethernet Channel)
it requires us to route one more pair of signals as a differential
pair.

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[Luke Kenneth Casson Leighton]

Post by Richard Wilbur
On the other hand, if we plan to support HEC (HDMI Ethernet Channel)
it requires us to route one more pair of signals as a differential
pair.

the micro-hdmi connector's pins are entirely packed out. i know that
there's no extra pins available (there's only 19, 1 of them unused),
and there are definitely no extra pads coming out from the A20 which
could be identified as HEC.

l.

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[Luke Kenneth Casson Leighton]

On Tue, Aug 1, 2017 at 6:45 AM, Andrew Bolin

Post by Andrew Bolin

so *i'm* not quotes considering it quotes - if it's there and there's
a linux kernel module it's there, people can compile it and use it.
l.

Can't use it if the pin has no connection to the CPU!
In the last screenshots I saw (
http://hands.com/~lkcl/eoma/a20_hdmi_review/scrn2.png ), pin 2 HEAC+
(ethernet/ARC) is not connected to anything.

... because the A20 doesn't have anything to connect it to.

l.

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[Luke Kenneth Casson Leighton]

---
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68

Audio Return channel[1]
Claims to be able to carry the signals normally routed over an S/PDIF
cable from the video signal receiver (sink) back to the video signal
transmitter (source).

yes. there exists a kernel module. absolutely no information is
available about how it works.... except as can be read in the source
code.

I'd love to download the specification but they have it behind a
signed agreement + steep pay wall.

yyeah.. not hugely gonna worry about it. if it works it works, if it
doesn't it doesn't.

l.

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[Richard Wilbur]

On Mon, Jul 31, 2017 at 11:45 PM, Andrew Bolin

Post by Andrew Bolin
Can't use it if the pin has no connection to the CPU!
In the last screenshots I saw (
http://hands.com/~lkcl/eoma/a20_hdmi_review/scrn2.png ), pin 2 HEAC+
(ethernet/ARC) is not connected to anything. Pin 1 (HEAC- & HPD) does go
somewhere, but it's of no use for these functions by itself.

I agree, sounds like HEAC (HDMI Ethernet/Audio Return Channel) won't
work as we don't have the pair connected to the CPU and that signal is
HEC -- differential, ARC -- single-ended.

On the other hand HPD (Hot-Plug Detect) should work.

Post by Andrew Bolin
CEC does seem to be routed and is mentioned on the A20 info page.
No SBC that I've seen actually uses these functions (unfortunately).

We'll have to see if we can make it work.

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