| ================= |
| ALSA BT87x Driver |
| ================= |
| |
| 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@alsa-project.org>, 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> |
