| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame^] | 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@lists.sf.net>, regardless of whether audio capture works or |
| 40 | 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> |