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Re: [Openvortex-dev] Re: au88x0 - Replace spdif frequency control by IEC

From: Manuel Jander
Subject: Re: [Openvortex-dev] Re: au88x0 - Replace spdif frequency control by IEC958 control
Date: Tue, 01 Mar 2005 11:09:42 -0300


On Tue, 2005-03-01 at 21:27 +0800, Raymond wrote:
>  >> The parameter 'spdif_mode' in the routine
>  >> vortex_spdif_init(vortex,spdif_sr,spdif_mode) in au88x0_core.c seems
>  >> to control AC3 passthrough.
>  >>
>  >> However the two memory mapped I/O VORTEX_SPDIF_CFG0 and
>  >> VORTEX_SPDIF_CFG1 seem to be write-only, return zero when read.
>  >Then we need to cache the values.

Just as we currently do with many other registers :)

> Define snd_aes_iec958_t spdif_out in struct snd_vortex in au88x0.h

> 3) Do we need to change the ADB routing when using AC3 passthrough ?

Hmm, good question. Maybe yes, because the current SPDIF PCM device
route does stereo deinterlacing (separating two stereo channels). The
SPDIF interface has 2 input sinks. For AC3 data, 2 interlaced channels
does not make ant sense, because it could be 4, 6 or more, encoded in
who knows what. Its just some raw data that must be passed through
intact. It may be that in AC3 passthrough mode the SPDIF transmitter
just re-joins the 2 data streams resulting in the original raw bit
stream, hopefuly not messing it up. Maybe someone with more SPDIF
knowledge can comment on this ?

> >
> > > 5) What additional kcontrol and routine are needed for SPDIF IN ?
> >

AFAIK, there is no direct SPDIF input interface on the au8830 chip. It
looks like that the SPDIF input is implemented using a I2S port or one
of the coporecessor interfaces. Since they are all sincronous serial
interfaces, they probably are almost the same and almost compatible
between each other, requiring little tweaking/additional circuitry on
the interface daughter-board.

> 5) How can STAC9721 stereo codec provide quad audio ? ( Is it through
> SPDIF-I2S link ? )

That depends on the hardware. AFAIK, the STAC9721 supports only 2
channels. If we want 4, then obviously, the other two must go through
any other codec. It could be a secondary STAC9721, a I2S codec connected
to the I2S interface, some other kind of codec/DSP connected to any of
the 8 coprocessor I/O interfaces, SPDIF, or whatever interfaces there
might be we don't even know about.

Best Regards
Manuel Jander
Electronic Engineer

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