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Documentation / sound / alsa / Bt87x.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

1	Intro
2	=====
3	
4	You might have noticed that the bt878 grabber cards have actually
5	_two_ PCI functions:
6	
7	$ lspci
8	[ ... ]
9	00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02)
10	00:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02)
11	[ ... ]
12	
13	The first does video, it is backward compatible to the bt848.  The second
14	does audio.  snd-bt87x is a driver for the second function.  It's a sound
15	driver which can be used for recording sound (and _only_ recording, no
16	playback).  As most TV cards come with a short cable which can be plugged
17	into your sound card's line-in you probably don't need this driver if all
18	you want to do is just watching TV...
19	
20	Some cards do not bother to connect anything to the audio input pins of
21	the chip, and some other cards use the audio function to transport MPEG
22	video data, so it's quite possible that audio recording may not work
23	with your card.
24	
25	
26	Driver Status
27	=============
28	
29	The driver is now stable.  However, it doesn't know about many TV cards,
30	and it refuses to load for cards it doesn't know.
31	
32	If the driver complains ("Unknown TV card found, the audio driver will
33	not load"), you can specify the load_all=1 option to force the driver to
34	try to use the audio capture function of your card.  If the frequency of
35	recorded data is not right, try to specify the digital_rate option with
36	other values than the default 32000 (often it's 44100 or 64000).
37	
38	If 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
40	or not, so that future versions of this driver know about your card.
41	
42	
43	Audio modes
44	===========
45	
46	The chip knows two different modes (digital/analog).  snd-bt87x
47	registers two PCM devices, one for each mode.  They cannot be used at
48	the same time.
49	
50	
51	Digital audio mode
52	==================
53	
54	The first device (hw:X,0) gives you 16 bit stereo sound.  The sample
55	rate depends on the external source which feeds the Bt87x with digital
56	sound via I2S interface.
57	
58	
59	Analog audio mode (A/D)
60	=======================
61	
62	The second device (hw:X,1) gives you 8 or 16 bit mono sound.  Supported
63	sample rates are between 119466 and 448000 Hz (yes, these numbers are
64	that high).  If you've set the CONFIG_SND_BT87X_OVERCLOCK option, the
65	maximum sample rate is 1792000 Hz, but audio data becomes unusable
66	beyond 896000 Hz on my card.
67	
68	The chip has three analog inputs.  Consequently you'll get a mixer
69	device to control these.
70	
71	
72	Have fun,
73	
74	  Clemens
75	
76	
77	Written by Clemens Ladisch <clemens@ladisch.de>
78	big parts copied from btaudio.txt by Gerd Knorr <kraxel@bytesex.org>
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