How to enable audio codec power saving

2007-03-24T19:45:30Z

Nischu: /* On-demand power control */

The AC97 sound device (e.g., AD1981B) requires a noticable amount of power (0.3W on {{T43}}). This power can be saved when the device is not in use.

==Disabling the device==
Disable the sound device by unloading modules or {{cmdroot|echo -n 3 > /sys/class/sound/controlC0/device/power/state}} (replace 3 by 0 to enable again).

==On-demand power control==
There's an [http://www.kernel.org/git/?p=linux/kernel/git/perex/alsa.git;a=commitdiff_plain;h=6dbe662874ba08585eaf732d126762c25ac8e3f7;hp=2b29b13c5794f648cd5e839796496704d787f5a6 experimental patch from 2.6.19-rc2], [http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff_plain;h=da43deb116c0cea9ca2174f2ac64985c4d53077e;hp=dbedca39fe30db87b6401e4396f959c63d90082e that was later corrected in 2.6.19-rc3], which enables the support of aggressive AC97 power-saving mode in the Linux [[ALSA]] drivers. In this mode, the AC97 powerdown register bits are dynamically controlled at each open/close of PCM streams. To allow powering off the analog mixer, make sure all analog inputs (Line, Microphone, CD, etc.) are muted.

It is working without a hitch in an IBM X31 with kernel 2.6.20.

The mode is disabled by default, and activated via <tt>power_save=1</tt> option for <tt>snd-ac97-codec</tt> driver (at run time, use {{cmdroot|echo Y > /sys/module/snd_ac97_codec/parameters/power_save}}).

You may hear a faint click each time the device is powered up (at start of playback) and each time the device is powered down (2 seconds after playback ends).

My machine consumes about 119 watts. After having enabled this power_save mode it consumes 117 watts if I don't play anything. Consider that your microphone has to be muted.

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How to enable audio codec power saving