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1 | ================= |
2 | ALSA BT87x Driver | |
3 | ================= | |
4 | ||
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5 | Intro |
6 | ===== | |
7 | ||
8 | You might have noticed that the bt878 grabber cards have actually | |
7bb97dfd TI |
9 | *two* PCI functions: |
10 | :: | |
1da177e4 | 11 | |
7bb97dfd TI |
12 | $ lspci |
13 | [ ... ] | |
14 | 00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02) | |
15 | 00:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02) | |
16 | [ ... ] | |
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17 | |
18 | The first does video, it is backward compatible to the bt848. The second | |
19 | does audio. snd-bt87x is a driver for the second function. It's a sound | |
7bb97dfd | 20 | driver which can be used for recording sound (and *only* recording, no |
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21 | playback). As most TV cards come with a short cable which can be plugged |
22 | into your sound card's line-in you probably don't need this driver if all | |
23 | you want to do is just watching TV... | |
24 | ||
25 | Some cards do not bother to connect anything to the audio input pins of | |
26 | the chip, and some other cards use the audio function to transport MPEG | |
27 | video data, so it's quite possible that audio recording may not work | |
28 | with your card. | |
29 | ||
30 | ||
31 | Driver Status | |
32 | ============= | |
33 | ||
34 | The driver is now stable. However, it doesn't know about many TV cards, | |
35 | and it refuses to load for cards it doesn't know. | |
36 | ||
37 | If the driver complains ("Unknown TV card found, the audio driver will | |
7bb97dfd | 38 | not load"), you can specify the ``load_all=1`` option to force the driver to |
1da177e4 | 39 | try to use the audio capture function of your card. If the frequency of |
7bb97dfd | 40 | recorded data is not right, try to specify the ``digital_rate`` option with |
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41 | other values than the default 32000 (often it's 44100 or 64000). |
42 | ||
43 | If you have an unknown card, please mail the ID and board name to | |
4505179c RH |
44 | <alsa-devel@alsa-project.org>, regardless of whether audio capture works |
45 | or not, so that future versions of this driver know about your card. | |
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46 | |
47 | ||
48 | Audio modes | |
49 | =========== | |
50 | ||
51 | The chip knows two different modes (digital/analog). snd-bt87x | |
52 | registers two PCM devices, one for each mode. They cannot be used at | |
53 | the same time. | |
54 | ||
55 | ||
56 | Digital audio mode | |
57 | ================== | |
58 | ||
59 | The first device (hw:X,0) gives you 16 bit stereo sound. The sample | |
60 | rate depends on the external source which feeds the Bt87x with digital | |
61 | sound via I2S interface. | |
62 | ||
63 | ||
64 | Analog audio mode (A/D) | |
65 | ======================= | |
66 | ||
67 | The second device (hw:X,1) gives you 8 or 16 bit mono sound. Supported | |
68 | sample rates are between 119466 and 448000 Hz (yes, these numbers are | |
69 | that high). If you've set the CONFIG_SND_BT87X_OVERCLOCK option, the | |
70 | maximum sample rate is 1792000 Hz, but audio data becomes unusable | |
71 | beyond 896000 Hz on my card. | |
72 | ||
73 | The chip has three analog inputs. Consequently you'll get a mixer | |
74 | device to control these. | |
75 | ||
76 | ||
77 | Have fun, | |
78 | ||
79 | Clemens | |
80 | ||
81 | ||
82 | Written by Clemens Ladisch <clemens@ladisch.de> | |
83 | big parts copied from btaudio.txt by Gerd Knorr <kraxel@bytesex.org> |