power managing maestro.c 0.14 available.

[Jens Axboe]

On Sat, Jan 29 2000, Jamie Lokier wrote:
> > You don't always need to fire up the audio device when a CD is played,
> > I frequently just use head phones plugged into the front of the drive.
> 
> I tried plugging headphones into one, and the output was horrible.  I'm
> surprised, because through the sound card, via two unshielded cables
> draped across the whole computer, it sounded pretty good.

That is odd, I usually find the quality of output to be much
better plugging directly in to the drive. Bad drive ;)

> Another drive doesn't have a headphone socket or volume control.
> Just a play button, oddly.

Yes, they do vary a lot.

> > Lets not talk IDE, but CD-ROM instead. All volume requests and CD
> > play operations go through the uniform CD-ROM layer. A drive
> > can fail the volume request naturally, if it doesn't support it.
> 
> I was thinking of a specific drive, the one I have at work.  It's an
> idea drive.  All cd player apps with a volume slider, ranging from 0% to
> 100%, give this behaviour: 0% == no sound, 1-99% == fixed volume.

In that case it does not fail, the drive just does not honor the
specifications. More below.

> > At probe time we also detect whether the drive does support CD
> > audio. Why would you need the specific volume? If there's some
> > kind of output, fire up the audio device. Some CD drives don't
> > even support a range of volumes, just on/off.
> 
> Precisely.  You'd want the specific volume from the application that's
> calling the uniform CD-ROM layer, so you can pass it to the audio mixer
> in the case that the drive only supports on/off.

Ah, I see what you mean.

> So my question is: can you detect the difference between a drive that
> only does on/off and a drive that has its own volume control?

Well, that depends on whether the drive internally keeps the volume
either at 0/0xff or the value we sent it. The one case I saw set the
volume to 0xff for any volume setting, so in that case we can
detect whether it honors the volume setting or not.

-- 
*  Jens Axboe <axboe en suse.de>
*  Linux CD-ROM Maintainer
*  http://www.kernel.dk

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