[alsa-devel] snd_ctl_elem_write fails -EPERM if snd_pcm is open

Pavel Hofman pavel.hofman at insite.cz
Tue Apr 15 20:33:13 CEST 2008

Bouterse, Bob wrote:
> I am trying to sent IEC958 status bits on a VT1708A HAD-INTEL codec
> while audio is being output.
> snd_ctl_elem_write returns -EPERM from
> linux- .
> Is there some way I can do this?
> FYI using iecset will also give you an:
> # iecset copywrite on
> snd_ctl_elem_write: Operation not permitted
> I am using alsa-lib-1.0.14a


I guess the reason is in /usr/share/alsa/cards/HDA-Intel.conf . If I 
understand correctly, upon opening the iec958 stream, the status bits 
control gets locked

			hook_args [
				name "IEC958 Playback Default"
				lock true
				preserve true
				value [ $AES0 $AES1 $AES2 $AES3 ]

The same applies to a number of other cards.


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