[alsa-devel] How can you tell if the speaker jack on your sound card has anything plugged into it???

Mark Brown broonie at opensource.wolfsonmicro.com
Fri Apr 25 23:55:31 CEST 2008

On Fri, Apr 25, 2008 at 02:32:42PM -0700, Tobin Davis wrote:

> The snd_hda_intel driver does this internally to mute the speakers when
> headphones are plugged in.  Ditto for front mic.  But you are right, we
> need a standard way of tracking this.  I am exploring the HAL interface
> now to see what I can learn from it.  And most sound chips have an

The interface I'd previously proposed here was to provide an input
device per-jack which would do this - hal should then be able to monitor
the input device.  As suggested in the original message in the thread
providing sysfs information would probably be helpful for scripts.

> insert detection mechanism.  Usually they are wired to specific jacks,
> but sometimes they just register a change in plug state, and read the
> jack's impedance levels to know which jack is used.  It is documented in
> the Sigmatel/IDT, Realtek, and Analog Devices codec PRMs.

Yes, that's how all the codecs I've looked at do this.

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