Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | |
2 | Intro | |
3 | ===== | |
4 | ||
5 | people start bugging me about this with questions, looks like I | |
6 | should write up some documentation for this beast. That way I | |
7 | don't have to answer that much mails I hope. Yes, I'm lazy... | |
8 | ||
9 | ||
10 | You might have noticed that the bt878 grabber cards have actually | |
11 | _two_ PCI functions: | |
12 | ||
13 | $ lspci | |
14 | [ ... ] | |
15 | 00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02) | |
16 | 00:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02) | |
17 | [ ... ] | |
18 | ||
19 | The first does video, it is backward compatible to the bt848. The second | |
20 | does audio. btaudio is a driver for the second function. It's a sound | |
21 | driver which can be used for recording sound (and _only_ recording, no | |
22 | playback). As most TV cards come with a short cable which can be plugged | |
23 | into your sound card's line-in you probably don't need this driver if all | |
24 | you want to do is just watching TV... | |
25 | ||
26 | ||
27 | Driver Status | |
28 | ============= | |
29 | ||
30 | Still somewhat experimental. The driver should work stable, i.e. it | |
31 | should'nt crash your box. It might not work as expected, have bugs, | |
32 | not being fully OSS API compilant, ... | |
33 | ||
34 | Latest versions are available from http://bytesex.org/bttv/, the | |
35 | driver is in the bttv tarball. Kernel patches might be available too, | |
36 | have a look at http://bytesex.org/bttv/listing.html. | |
37 | ||
38 | The chip knows two different modes. btaudio registers two dsp | |
39 | devices, one for each mode. They can not be used at the same time. | |
40 | ||
41 | ||
42 | Digital audio mode | |
43 | ================== | |
44 | ||
45 | The chip gives you 16 bit stereo sound. The sample rate depends on | |
46 | the external source which feeds the bt878 with digital sound via I2S | |
47 | interface. There is a insmod option (rate) to tell the driver which | |
48 | sample rate the hardware uses (32000 is the default). | |
49 | ||
50 | One possible source for digital sound is the msp34xx audio processor | |
51 | chip which provides digital sound via I2S with 32 kHz sample rate. My | |
52 | Hauppauge board works this way. | |
53 | ||
54 | The Osprey-200 reportly gives you digital sound with 44100 Hz sample | |
55 | rate. It is also possible that you get no sound at all. | |
56 | ||
57 | ||
58 | analog mode (A/D) | |
59 | ================= | |
60 | ||
61 | You can tell the driver to use this mode with the insmod option "analog=1". | |
62 | The chip has three analog inputs. Consequently you'll get a mixer device | |
63 | to control these. | |
64 | ||
65 | The analog mode supports mono only. Both 8 + 16 bit. Both are _signed_ | |
66 | int, which is uncommon for the 8 bit case. Sample rate range is 119 kHz | |
67 | to 448 kHz. Yes, the number of digits is correct. The driver supports | |
68 | downsampling by powers of two, so you can ask for more usual sample rates | |
69 | like 44 kHz too. | |
70 | ||
71 | With my Hauppauge I get noisy sound on the second input (mapped to line2 | |
72 | by the mixer device). Others get a useable signal on line1. | |
73 | ||
74 | ||
75 | some 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 | ||
87 | Have fun, | |
88 | ||
89 | Gerd | |
90 | ||
91 | -- | |
92 | Gerd Knorr <kraxel@bytesex.org> |