How to enable audio codec power saving

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Revision as of 15:46, 24 October 2006 by Hmh (Talk | contribs) (→‎On-demand power control: add link to 2.6.19-rc3 ac97 powersave fix)
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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 # echo -n 3 > /sys/class/sound/controlC0/device/power/state (replace 3 by 0 to enable again).

On-demand power control

There's an experimental patch from 2.6.19-rc2, 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.

The mode is disabled by default, and activated via power_save=1 option for snd-ac97-codec driver (at run time, use # 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).

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