| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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> |