| |
| Intro |
| ===== |
| |
| people start bugging me about this with questions, looks like I |
| should write up some documentation for this beast. That way I |
| don't have to answer that much mails I hope. Yes, I'm lazy... |
| |
| |
| You might have noticed that the bt878 grabber cards have actually |
| _two_ PCI functions: |
| |
| $ lspci |
| [ ... ] |
| 00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02) |
| 00:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02) |
| [ ... ] |
| |
| The first does video, it is backward compatible to the bt848. The second |
| does audio. btaudio is a driver for the second function. It's a sound |
| driver which can be used for recording sound (and _only_ recording, no |
| playback). As most TV cards come with a short cable which can be plugged |
| into your sound card's line-in you probably don't need this driver if all |
| you want to do is just watching TV... |
| |
| |
| Driver Status |
| ============= |
| |
| Still somewhat experimental. The driver should work stable, i.e. it |
| should'nt crash your box. It might not work as expected, have bugs, |
| not being fully OSS API compilant, ... |
| |
| Latest versions are available from http://bytesex.org/bttv/, the |
| driver is in the bttv tarball. Kernel patches might be available too, |
| have a look at http://bytesex.org/bttv/listing.html. |
| |
| The chip knows two different modes. btaudio registers two dsp |
| devices, one for each mode. They can not be used at the same time. |
| |
| |
| Digital audio mode |
| ================== |
| |
| The chip gives you 16 bit stereo sound. The sample rate depends on |
| the external source which feeds the bt878 with digital sound via I2S |
| interface. There is a insmod option (rate) to tell the driver which |
| sample rate the hardware uses (32000 is the default). |
| |
| One possible source for digital sound is the msp34xx audio processor |
| chip which provides digital sound via I2S with 32 kHz sample rate. My |
| Hauppauge board works this way. |
| |
| The Osprey-200 reportly gives you digital sound with 44100 Hz sample |
| rate. It is also possible that you get no sound at all. |
| |
| |
| analog mode (A/D) |
| ================= |
| |
| You can tell the driver to use this mode with the insmod option "analog=1". |
| The chip has three analog inputs. Consequently you'll get a mixer device |
| to control these. |
| |
| The analog mode supports mono only. Both 8 + 16 bit. Both are _signed_ |
| int, which is uncommon for the 8 bit case. Sample rate range is 119 kHz |
| to 448 kHz. Yes, the number of digits is correct. The driver supports |
| downsampling by powers of two, so you can ask for more usual sample rates |
| like 44 kHz too. |
| |
| With my Hauppauge I get noisy sound on the second input (mapped to line2 |
| by the mixer device). Others get a useable signal on line1. |
| |
| |
| some examples |
| ============= |
| |
| * read audio data from btaudio (dsp2), send to es1730 (dsp,dsp1): |
| $ sox -w -r 32000 -t ossdsp /dev/dsp2 -t ossdsp /dev/dsp |
| |
| * read audio data from btaudio, send to esound daemon (which might be |
| running on another host): |
| $ sox -c 2 -w -r 32000 -t ossdsp /dev/dsp2 -t sw - | esdcat -r 32000 |
| $ sox -c 1 -w -r 32000 -t ossdsp /dev/dsp2 -t sw - | esdcat -m -r 32000 |
| |
| |
| Have fun, |
| |
| Gerd |
| |
| -- |
| Gerd Knorr <kraxel@bytesex.org> |