0001 =================
0002 ALSA BT87x Driver
0003 =================
0004
0005 Intro
0006 =====
0007
0008 You might have noticed that the bt878 grabber cards have actually
0009 *two* PCI functions:
0010 ::
0011
0012 $ lspci
0013 [ ... ]
0014 00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02)
0015 00:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02)
0016 [ ... ]
0017
0018 The first does video, it is backward compatible to the bt848. The second
0019 does audio. snd-bt87x is a driver for the second function. It's a sound
0020 driver which can be used for recording sound (and *only* recording, no
0021 playback). As most TV cards come with a short cable which can be plugged
0022 into your sound card's line-in you probably don't need this driver if all
0023 you want to do is just watching TV...
0024
0025 Some cards do not bother to connect anything to the audio input pins of
0026 the chip, and some other cards use the audio function to transport MPEG
0027 video data, so it's quite possible that audio recording may not work
0028 with your card.
0029
0030
0031 Driver Status
0032 =============
0033
0034 The driver is now stable. However, it doesn't know about many TV cards,
0035 and it refuses to load for cards it doesn't know.
0036
0037 If the driver complains ("Unknown TV card found, the audio driver will
0038 not load"), you can specify the ``load_all=1`` option to force the driver to
0039 try to use the audio capture function of your card. If the frequency of
0040 recorded data is not right, try to specify the ``digital_rate`` option with
0041 other values than the default 32000 (often it's 44100 or 64000).
0042
0043 If you have an unknown card, please mail the ID and board name to
0044 <alsa-devel@alsa-project.org>, regardless of whether audio capture works
0045 or not, so that future versions of this driver know about your card.
0046
0047
0048 Audio modes
0049 ===========
0050
0051 The chip knows two different modes (digital/analog). snd-bt87x
0052 registers two PCM devices, one for each mode. They cannot be used at
0053 the same time.
0054
0055
0056 Digital audio mode
0057 ==================
0058
0059 The first device (hw:X,0) gives you 16 bit stereo sound. The sample
0060 rate depends on the external source which feeds the Bt87x with digital
0061 sound via I2S interface.
0062
0063
0064 Analog audio mode (A/D)
0065 =======================
0066
0067 The second device (hw:X,1) gives you 8 or 16 bit mono sound. Supported
0068 sample rates are between 119466 and 448000 Hz (yes, these numbers are
0069 that high). If you've set the CONFIG_SND_BT87X_OVERCLOCK option, the
0070 maximum sample rate is 1792000 Hz, but audio data becomes unusable
0071 beyond 896000 Hz on my card.
0072
0073 The chip has three analog inputs. Consequently you'll get a mixer
0074 device to control these.
0075
0076
0077 Have fun,
0078
0079 Clemens
0080
0081
0082 Written by Clemens Ladisch <clemens@ladisch.de>
0083 big parts copied from btaudio.txt by Gerd Knorr <kraxel@bytesex.org>
