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Old 05-04-09, 11:33 AM   #8
wck555
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Join Date: Apr 2009
Posts: 9
Default Re: Problems with audio over HDMI on Apple TV

Another test further confirms that by default the SiI 1390 chip embeds audio data in the HDMI stream, but when nvidia driver starts, it disables the audio data.

Previously I was not able to switch between the nvidia driver and the nv driver without rebooting. Version 180.51 of the nvidia driver did something to the video configuration that the nv driver could not undo. However I got an older version of the nvidia driver (96.43.09) and now I am able to switch back and forth. Version 96.43.09 is a legacy nvidia driver updated with work with new Linux kernals. Here's the test:

- Configure X for nv driver and boot. No audio over RCA. HMDI audio works after X starts
- Restart X with nvidia driver. As soon as nVidia logo appears, TV starts playing audio over RCA. HDMI audio stops working.
- Stop X. TV still playing audio over RCA
- Reload alsa (alsa reload) and then examine /proc/asound/card0/codec#1, it has returned to the "good" state (Digital: Enabled, etc). Audio still coming over RCA
- Restart X with nv driver. Audio still playing over RCA. HDMI audio does not work.

I was surprised the nvidia driver 96.43.09 disabled HDMI audio. I thought HDMI audio would work with older nvidia drivers. I am not able to run version 100.14.19 on my kernal (Ubuntu 8.10 - kernel 2.6.27-11-generic). So I cannot confirm HDMI audio works with 100.14.19 as other people have observed.

Once again it comes down to the SiI 1390 chip. I either need to prevent nvidia from messing with the 1390 or restore the 1390 to it's default state after the nvidia driver starts.

There's a whole class of undocumented nvidia settings (ex: Option "RegistryDwords" "RMDisableRenderToSysmem=1") that could hold a key to doing this. I would love to find a source of information on these settings.
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