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@@ -1092,8 +1092,8 @@ WARNING:
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its level up and down at every change.
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-Volume control
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---------------
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+Volume control (Console Audio control)
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+--------------------------------------
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procfs: /proc/acpi/ibm/volume
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ALSA: "ThinkPad Console Audio Control", default ID: "ThinkPadEC"
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@@ -1110,9 +1110,53 @@ the desktop environment to just provide on-screen-display feedback.
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Software volume control should be done only in the main AC97/HDA
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mixer.
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-This feature allows volume control on ThinkPad models with a digital
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-volume knob (when available, not all models have it), as well as
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-mute/unmute control. The available commands are:
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+
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+About the ThinkPad Console Audio control:
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+
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+ThinkPads have a built-in amplifier and muting circuit that drives the
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+console headphone and speakers. This circuit is after the main AC97
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+or HDA mixer in the audio path, and under exclusive control of the
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+firmware.
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+
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+ThinkPads have three special hotkeys to interact with the console
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+audio control: volume up, volume down and mute.
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+
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+It is worth noting that the normal way the mute function works (on
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+ThinkPads that do not have a "mute LED") is:
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+
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+1. Press mute to mute. It will *always* mute, you can press it as
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+ many times as you want, and the sound will remain mute.
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+
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+2. Press either volume key to unmute the ThinkPad (it will _not_
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+ change the volume, it will just unmute).
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+
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+This is a very superior design when compared to the cheap software-only
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+mute-toggle solution found on normal consumer laptops: you can be
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+absolutely sure the ThinkPad will not make noise if you press the mute
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+button, no matter the previous state.
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+
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+The IBM ThinkPads, and the earlier Lenovo ThinkPads have variable-gain
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+amplifiers driving the speakers and headphone output, and the firmware
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+also handles volume control for the headphone and speakers on these
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+ThinkPads without any help from the operating system (this volume
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+control stage exists after the main AC97 or HDA mixer in the audio
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+path).
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+
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+The newer Lenovo models only have firmware mute control, and depend on
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+the main HDA mixer to do volume control (which is done by the operating
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+system). In this case, the volume keys are filtered out for unmute
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+key press (there are some firmware bugs in this area) and delivered as
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+normal key presses to the operating system (thinkpad-acpi is not
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+involved).
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+
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+
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+The ThinkPad-ACPI volume control:
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+
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+The preferred way to interact with the Console Audio control is the
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+ALSA interface.
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+
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+The legacy procfs interface allows one to read the current state,
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+and if volume control is enabled, accepts the following commands:
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echo up >/proc/acpi/ibm/volume
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echo down >/proc/acpi/ibm/volume
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@@ -1121,12 +1165,10 @@ mute/unmute control. The available commands are:
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echo 'level <level>' >/proc/acpi/ibm/volume
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The <level> number range is 0 to 14 although not all of them may be
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-distinct. The unmute the volume after the mute command, use either the
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+distinct. To unmute the volume after the mute command, use either the
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up or down command (the level command will not unmute the volume), or
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the unmute command.
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-The current volume level and mute state is shown in the file.
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-
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You can use the volume_capabilities parameter to tell the driver
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whether your thinkpad has volume control or mute-only control:
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volume_capabilities=1 for mixers with mute and volume control,
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Henrique de Moraes Holschuh