mirror of https://gitee.com/openkylin/linux.git
84 lines
2.6 KiB
ReStructuredText
84 lines
2.6 KiB
ReStructuredText
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=================
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ALSA BT87x Driver
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=================
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Intro
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=====
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You might have noticed that the bt878 grabber cards have actually
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*two* PCI functions:
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::
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$ lspci
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[ ... ]
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00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02)
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00:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02)
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[ ... ]
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The first does video, it is backward compatible to the bt848. The second
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does audio. snd-bt87x is a driver for the second function. It's a sound
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driver which can be used for recording sound (and *only* recording, no
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playback). As most TV cards come with a short cable which can be plugged
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into your sound card's line-in you probably don't need this driver if all
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you want to do is just watching TV...
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Some cards do not bother to connect anything to the audio input pins of
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the chip, and some other cards use the audio function to transport MPEG
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video data, so it's quite possible that audio recording may not work
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with your card.
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Driver Status
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=============
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The driver is now stable. However, it doesn't know about many TV cards,
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and it refuses to load for cards it doesn't know.
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If the driver complains ("Unknown TV card found, the audio driver will
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not load"), you can specify the ``load_all=1`` option to force the driver to
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try to use the audio capture function of your card. If the frequency of
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recorded data is not right, try to specify the ``digital_rate`` option with
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other values than the default 32000 (often it's 44100 or 64000).
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If you have an unknown card, please mail the ID and board name to
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<alsa-devel@alsa-project.org>, regardless of whether audio capture works
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or not, so that future versions of this driver know about your card.
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Audio modes
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===========
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The chip knows two different modes (digital/analog). snd-bt87x
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registers two PCM devices, one for each mode. They cannot be used at
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the same time.
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Digital audio mode
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==================
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The first device (hw:X,0) gives you 16 bit stereo sound. The sample
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rate depends on the external source which feeds the Bt87x with digital
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sound via I2S interface.
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Analog audio mode (A/D)
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=======================
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The second device (hw:X,1) gives you 8 or 16 bit mono sound. Supported
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sample rates are between 119466 and 448000 Hz (yes, these numbers are
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that high). If you've set the CONFIG_SND_BT87X_OVERCLOCK option, the
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maximum sample rate is 1792000 Hz, but audio data becomes unusable
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beyond 896000 Hz on my card.
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The chip has three analog inputs. Consequently you'll get a mixer
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device to control these.
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Have fun,
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Clemens
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Written by Clemens Ladisch <clemens@ladisch.de>
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big parts copied from btaudio.txt by Gerd Knorr <kraxel@bytesex.org>
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