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