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diff --git a/Documentation/sound/oss/btaudio b/Documentation/sound/oss/btaudio new file mode 100644 index 00000000000..1a693e69d44 --- /dev/null +++ b/Documentation/sound/oss/btaudio @@ -0,0 +1,92 @@ + +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> |