linux/Documentation/sound/alsa/Bt87x.txt
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   1Intro
   2=====
   3
   4You might have noticed that the bt878 grabber cards have actually
   5_two_ PCI functions:
   6
   7$ lspci
   8[ ... ]
   900:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02)
  1000:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02)
  11[ ... ]
  12
  13The first does video, it is backward compatible to the bt848.  The second
  14does audio.  snd-bt87x is a driver for the second function.  It's a sound
  15driver which can be used for recording sound (and _only_ recording, no
  16playback).  As most TV cards come with a short cable which can be plugged
  17into your sound card's line-in you probably don't need this driver if all
  18you want to do is just watching TV...
  19
  20Some cards do not bother to connect anything to the audio input pins of
  21the chip, and some other cards use the audio function to transport MPEG
  22video data, so it's quite possible that audio recording may not work
  23with your card.
  24
  25
  26Driver Status
  27=============
  28
  29The driver is now stable.  However, it doesn't know about many TV cards,
  30and it refuses to load for cards it doesn't know.
  31
  32If the driver complains ("Unknown TV card found, the audio driver will
  33not load"), you can specify the load_all=1 option to force the driver to
  34try to use the audio capture function of your card.  If the frequency of
  35recorded data is not right, try to specify the digital_rate option with
  36other values than the default 32000 (often it's 44100 or 64000).
  37
  38If you have an unknown card, please mail the ID and board name to
  39<alsa-devel@alsa-project.org>, regardless of whether audio capture works
  40or not, so that future versions of this driver know about your card.
  41
  42
  43Audio modes
  44===========
  45
  46The chip knows two different modes (digital/analog).  snd-bt87x
  47registers two PCM devices, one for each mode.  They cannot be used at
  48the same time.
  49
  50
  51Digital audio mode
  52==================
  53
  54The first device (hw:X,0) gives you 16 bit stereo sound.  The sample
  55rate depends on the external source which feeds the Bt87x with digital
  56sound via I2S interface.
  57
  58
  59Analog audio mode (A/D)
  60=======================
  61
  62The second device (hw:X,1) gives you 8 or 16 bit mono sound.  Supported
  63sample rates are between 119466 and 448000 Hz (yes, these numbers are
  64that high).  If you've set the CONFIG_SND_BT87X_OVERCLOCK option, the
  65maximum sample rate is 1792000 Hz, but audio data becomes unusable
  66beyond 896000 Hz on my card.
  67
  68The chip has three analog inputs.  Consequently you'll get a mixer
  69device to control these.
  70
  71
  72Have fun,
  73
  74  Clemens
  75
  76
  77Written by Clemens Ladisch <clemens@ladisch.de>
  78big parts copied from btaudio.txt by Gerd Knorr <kraxel@bytesex.org>
  79