IEC switch issues

IEC switch issues

[pl bossart]

If I play my AC3 data on my HDAudio/SPDIF output using the hw:0,1
device, I can use alsamixer/amixer to mute/unmute.

[ume@plb PassThough]$ amixer cset numid=12 on
numid=12,iface=MIXER,name='IEC958 Playback Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on
[ume@plb PassThough]$ amixer cset numid=12 off
numid=12,iface=MIXER,name='IEC958 Playback Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=off

Now if I use the iec958: plugin, I can't control the mute switch any longer:
[ume@plb PassThough]$ amixer cset numid=12 off
amixer: Control default element write error: Operation not permitted

[ume@plb PassThough]$ amixer cset numid=12 on
amixer: Control default element write error: Operation not permitted

What could possibly cause this issue? the IEC plugin relies on the
device 1, am I missing something here?
Thanks for your help
- Pierre

Re: IEC switch issues

[Pavel Hofman]

pl bossart napsal(a):
> If I play my AC3 data on my HDAudio/SPDIF output using the hw:0,1
> device, I can use alsamixer/amixer to mute/unmute.
> 
> [ume@plb PassThough]$ amixer cset numid=12 on
> numid=12,iface=MIXER,name='IEC958 Playback Switch'
>   ; type=BOOLEAN,access=rw------,values=1
>   : values=on
> [ume@plb PassThough]$ amixer cset numid=12 off
> numid=12,iface=MIXER,name='IEC958 Playback Switch'
>   ; type=BOOLEAN,access=rw------,values=1
>   : values=off
> 
> Now if I use the iec958: plugin, I can't control the mute switch any longer:
> [ume@plb PassThough]$ amixer cset numid=12 off
> amixer: Control default element write error: Operation not permitted
> 
> [ume@plb PassThough]$ amixer cset numid=12 on
> amixer: Control default element write error: Operation not permitted
> 
> What could possibly cause this issue? the IEC plugin relies on the
> device 1, am I missing something here?
> Thanks for your help
> - Pierre

Hi Pierre,

Check the config files in /usr/share/alsa/cards, probably HDA-Intel.conf
in your case, specifically the hooks section of its iec958 device
definition. It reads:

hooks.0 {
                        type ctl_elems
                        hook_args [
                        {
                                name "IEC958 Playback Default"
                                lock true
                                preserve true
                                value [ $AES0 $AES1 $AES2 $AES3 ]
                        }
                        {
                                name "IEC958 Playback Switch"
                                lock true
                                preserve true
                                value true
                        }
                        ]
                }


You can play with the "lock" directive.

Best regards,

Pavel.

Re: IEC switch issues

[Clemens Ladisch]

pl bossart wrote:
> If I play my AC3 data on my HDAudio/SPDIF output using the hw:0,1
> device, I can use alsamixer/amixer to mute/unmute.
> 
> Now if I use the iec958: plugin, I can't control the mute switch any longer:

Muting an AC-3 stream would require encoding a stream of silent PCM
samples (no data is not the same as silence); therefore, the iec958
plugin disallows muting.


Regards,
Clemens

Re: IEC switch issues

[Raymond Yau]

2010/6/23 Clemens Ladisch <clemens@ladisch.de>

> pl bossart wrote:
> > If I play my AC3 data on my HDAudio/SPDIF output using the hw:0,1
> > device, I can use alsamixer/amixer to mute/unmute.
> >
> > Now if I use the iec958: plugin, I can't control the mute switch any
> longer:
>
> Muting an AC-3 stream would require encoding a stream of silent PCM
> samples (no data is not the same as silence); therefore, the iec958
> plugin disallows muting.
>
>
> Regards,
> Clemens
>
>
Does it mean that rewind is not allowed too ?

Re: IEC switch issues

[pl bossart]

>> If I play my AC3 data on my HDAudio/SPDIF output using the hw:0,1
>> device, I can use alsamixer/amixer to mute/unmute.
>>
>> Now if I use the iec958: plugin, I can't control the mute switch any longer:
>
> Muting an AC-3 stream would require encoding a stream of silent PCM
> samples (no data is not the same as silence); therefore, the iec958
> plugin disallows muting.

Actually the problem happens also with plain PCM rendered on the
iec958 device.There's no way to use the IEC switch.
So why do we have an S/PDIF switch in the first place? If it cannot be
used when you sent IEC-formatted data (be that PCM or AC3-formatted
data), then why bother?
Allowing for mute doesn't have any impact on functionality, and it
prevents the user from muting with alsamixer or a gui. I find this
silly, or I am missing something.

Re: IEC switch issues

[Clemens Ladisch]

pl bossart wrote:
>>> If I play my AC3 data on my HDAudio/SPDIF output using the hw:0,1
>>> device, I can use alsamixer/amixer to mute/unmute.
>>>
>>> Now if I use the iec958: plugin, I can't control the mute switch any longer:
>>
>> Muting an AC-3 stream would require encoding a stream of silent PCM
>> samples (no data is not the same as silence); therefore, the iec958
>> plugin disallows muting.
> 
> Actually the problem happens also with plain PCM rendered on the
> iec958 device.There's no way to use the IEC switch.
> So why do we have an S/PDIF switch in the first place?

Because the hardware has this switch; the driver just exposes all
hardware features.  

> If it cannot be used when you sent IEC-formatted data (be that PCM
> or AC3-formatted data), then why bother?

Some codecs allow looping back the ADC output to the SPDIF transmitter.
In these cases, disabling the SPDIF transmitter might be useful.


Regards,
Clemens

Re: IEC switch issues

[pl bossart]

>> Actually the problem happens also with plain PCM rendered on the
>> iec958 device.There's no way to use the IEC switch.
>> So why do we have an S/PDIF switch in the first place?
>
> Because the hardware has this switch; the driver just exposes all
> hardware features.

Then why not use it if it is supported by the hardware? Usually we use
software as a workaround for hw limitations, not software to prevent
use of hardware features.

> Some codecs allow looping back the ADC output to the SPDIF transmitter.
> In these cases, disabling the SPDIF transmitter might be useful.

I am not sure I understand how your remark is related to the problem I
reported. Yes disabling SPDIF whenever needed is a must. And no
there's no risk with enabling the IEC switch when rendering on the
iec958 device. I have IEC-formatted data, with C,U,V,P bits and
preambles, this could not possibly be sent to anything else than the
digital output.
Again the IEC switch is functionally equivalent to a mute, and it
shows as such in alsamixer with the MM symbol: the data keeps being
rendered, only the receiver doesn't detect valid data (no sync
detected) and will go to silence with an appropriate ramp. For AC3
passthrough, the filter history will be reset when the sync is lost,
and that will cause an implicit fade-out/fade-in in addition to the
PCM ramp. There is no need as you asserted to send zeroes instead.
Removing the 'lock true' in /usr/share/alsa/cards/HDA-Intel.conf h
works just fine to enable IEC controls. Thanks Pavel for the pointer.
I suggest we modify this to remove artificial functionality
limitations.