| 1 |
1275 |
phoenix |
|
| 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
|
