![Linus Torvalds](/assets/img/avatar_default.png)
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
79 lines
2.5 KiB
Plaintext
79 lines
2.5 KiB
Plaintext
Intro
|
|
=====
|
|
|
|
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. snd-bt87x 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...
|
|
|
|
Some cards do not bother to connect anything to the audio input pins of
|
|
the chip, and some other cards use the audio function to transport MPEG
|
|
video data, so it's quite possible that audio recording may not work
|
|
with your card.
|
|
|
|
|
|
Driver Status
|
|
=============
|
|
|
|
The driver is now stable. However, it doesn't know about many TV cards,
|
|
and it refuses to load for cards it doesn't know.
|
|
|
|
If the driver complains ("Unknown TV card found, the audio driver will
|
|
not load"), you can specify the load_all=1 option to force the driver to
|
|
try to use the audio capture function of your card. If the frequency of
|
|
recorded data is not right, try to specify the digital_rate option with
|
|
other values than the default 32000 (often it's 44100 or 64000).
|
|
|
|
If you have an unknown card, please mail the ID and board name to
|
|
<alsa-devel@lists.sf.net>, regardless of whether audio capture works or
|
|
not, so that future versions of this driver know about your card.
|
|
|
|
|
|
Audio modes
|
|
===========
|
|
|
|
The chip knows two different modes (digital/analog). snd-bt87x
|
|
registers two PCM devices, one for each mode. They cannot be used at
|
|
the same time.
|
|
|
|
|
|
Digital audio mode
|
|
==================
|
|
|
|
The first device (hw:X,0) gives you 16 bit stereo sound. The sample
|
|
rate depends on the external source which feeds the Bt87x with digital
|
|
sound via I2S interface.
|
|
|
|
|
|
Analog audio mode (A/D)
|
|
=======================
|
|
|
|
The second device (hw:X,1) gives you 8 or 16 bit mono sound. Supported
|
|
sample rates are between 119466 and 448000 Hz (yes, these numbers are
|
|
that high). If you've set the CONFIG_SND_BT87X_OVERCLOCK option, the
|
|
maximum sample rate is 1792000 Hz, but audio data becomes unusable
|
|
beyond 896000 Hz on my card.
|
|
|
|
The chip has three analog inputs. Consequently you'll get a mixer
|
|
device to control these.
|
|
|
|
|
|
Have fun,
|
|
|
|
Clemens
|
|
|
|
|
|
Written by Clemens Ladisch <clemens@ladisch.de>
|
|
big parts copied from btaudio.txt by Gerd Knorr <kraxel@bytesex.org>
|