[alsa-devel] Wrong channel order with multichannel HDMI on MCP7A

Anssi Hannula anssi.hannula at iki.fi
Sun Jul 25 18:51:39 CEST 2010

Hi all!

I have a motherboard with NVIDIA MCP7A HDMI audio.
However, multichannel audio is not mapped properly into the HDMI order.

On 5.1, I get RL in FC, RR in LFE, FC in RL, LFE in RR.

Interestingly, this is not consistent with the ALSA channel order (FL FR RL RR 
FC LFE) being passed directly to HDMI (FL FR LFE FC RL RR). Instead it looks 
like there has been a waveformatex (FL FR FC LFE RL RR; windows?) => HDMI 
conversion instead of ALSA => HDMI.

Same happens for 7.1.

Is it possible to set the hardware to do an ALSA => HDMI conversion instead?
If not, we should manually compensate for this somewhere, right?

Somewhat relatedly, trying to output 4 channels results in silence only. 
Trying to output 3 or 5 channels triggers a timeout with I/O error, with the 
following in the kernel log: "ALSA pcm_lib.c:1757: playback write error (DMA 
or IRQ trouble?)"

I used a git alsa-kmirror from few days ago on 2.6.35-rc4 for testing. 
Speaker-test and alsa-lib were 1.0.23.

Anssi Hannula

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