1
2Intro
3=====
4
5people start bugging me about this with questions, looks like I
6should write up some documentation for this beast.  That way I
7don't have to answer that much mails I hope.  Yes, I'm lazy...
8
9
10You might have noticed that the bt878 grabber cards have actually
11_two_ PCI functions:
12
13$ lspci
14[ ... ]
1500:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02)
1600:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02)
17[ ... ]
18
19The first does video, it is backward compatible to the bt848.  The second
20does audio.  btaudio is a driver for the second function.  It's a sound
21driver which can be used for recording sound (and _only_ recording, no
22playback).  As most TV cards come with a short cable which can be plugged
23into your sound card's line-in you probably don't need this driver if all
24you want to do is just watching TV...
25
26
27Driver Status
28=============
29
30Still somewhat experimental.  The driver should work stable, i.e. it
31should'nt crash your box.  It might not work as expected, have bugs,
32not being fully OSS API compliant, ...
33
34Latest versions are available from http://bytesex.org/bttv/, the
35driver is in the bttv tarball.  Kernel patches might be available too,
36have a look at http://bytesex.org/bttv/listing.html.
37
38The chip knows two different modes.  btaudio registers two dsp
39devices, one for each mode.  They can not be used at the same time.
40
41
42Digital audio mode
43==================
44
45The chip gives you 16 bit stereo sound.  The sample rate depends on
46the external source which feeds the bt878 with digital sound via I2S
47interface.  There is a insmod option (rate) to tell the driver which
48sample rate the hardware uses (32000 is the default).
49
50One possible source for digital sound is the msp34xx audio processor
51chip which provides digital sound via I2S with 32 kHz sample rate.  My
52Hauppauge board works this way.
53
54The Osprey-200 reportly gives you digital sound with 44100 Hz sample
55rate.  It is also possible that you get no sound at all.
56
57
58analog mode (A/D)
59=================
60
61You can tell the driver to use this mode with the insmod option "analog=1".
62The chip has three analog inputs.  Consequently you'll get a mixer device
63to control these.
64
65The analog mode supports mono only.  Both 8 + 16 bit.  Both are _signed_
66int, which is uncommon for the 8 bit case.  Sample rate range is 119 kHz
67to 448 kHz.  Yes, the number of digits is correct.  The driver supports
68downsampling by powers of two, so you can ask for more usual sample rates
69like 44 kHz too.
70
71With my Hauppauge I get noisy sound on the second input (mapped to line2
72by the mixer device).  Others get a useable signal on line1.
73
74
75some examples
76=============
77
78* read audio data from btaudio (dsp2), send to es1730 (dsp,dsp1):
79  $ sox -w -r 32000 -t ossdsp /dev/dsp2 -t ossdsp /dev/dsp
80
81* read audio data from btaudio, send to esound daemon (which might be
82  running on another host):
83  $ sox -c 2 -w -r 32000 -t ossdsp /dev/dsp2 -t sw - | esdcat -r 32000
84  $ sox -c 1 -w -r 32000 -t ossdsp /dev/dsp2 -t sw - | esdcat -m -r 32000
85
86
87Have fun,
88
89  Gerd
90
91-- 
92Gerd Knorr <kraxel@bytesex.org>
93