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#1 2017-01-15 20:46:59

mosquitogang201
Member
Registered: 2012-06-19
Posts: 37

[solved] How can I force audio output over HDMI

I have an Intel board using onboard graphics and connected to a TV via HDMI. When the computer is booted with the TV on, video and audio work perfectly over HDMI. When booted with the TV off, the HDMI port doesn't work. I've found I can force HDMI video output to on by appending the following kernel parameters at boot.

drm_kms_helper.edid_firmware=DP-1:edid/47le5400.bin video=DP-1:e

This doesn't enable audio output though. Is there a similar parameter that will force the audio output over HDMI?

Last edited by mosquitogang201 (2017-01-27 03:58:02)

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#2 2017-01-27 03:57:40

mosquitogang201
Member
Registered: 2012-06-19
Posts: 37

Re: [solved] How can I force audio output over HDMI

I can mark this solved. Here's what I did.

The HDMI spec states that pin 19 is to be pulled up to +5V when the display is active and pulled to ground when the display is unavailable. The spec also states that the display's EDID should be readable even when the display turned off. So, I opened up and modified an HDMI cable. On the sink side (TV side) I disconnected pin 19 (hot plug detect). On the source side (computer side), I tied pin 18 (+5V) to pin 19 with a 2.2K resistor. Now the computer thinks the TV is always available, and most importantly, is still able to read the EDID with the TV turned off. Works perfectly and I was able to remove the above mentioned kernel parameters.

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