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