1================= 2ALSA BT87x Driver 3================= 4 5Intro 6===== 7 8You might have noticed that the bt878 grabber cards have actually 9*two* PCI functions: 10:: 11 12 $ lspci 13 [ ... ] 14 00:0a.0 Multimedia video controller: Brooktree Corporation Bt878 (rev 02) 15 00:0a.1 Multimedia controller: Brooktree Corporation Bt878 (rev 02) 16 [ ... ] 17 18The first does video, it is backward compatible to the bt848. The second 19does audio. snd-bt87x is a driver for the second function. It's a sound 20driver which can be used for recording sound (and *only* recording, no 21playback). As most TV cards come with a short cable which can be plugged 22into your sound card's line-in you probably don't need this driver if all 23you want to do is just watching TV... 24 25Some cards do not bother to connect anything to the audio input pins of 26the chip, and some other cards use the audio function to transport MPEG 27video data, so it's quite possible that audio recording may not work 28with your card. 29 30 31Driver Status 32============= 33 34The driver is now stable. However, it doesn't know about many TV cards, 35and it refuses to load for cards it doesn't know. 36 37If the driver complains ("Unknown TV card found, the audio driver will 38not load"), you can specify the ``load_all=1`` option to force the driver to 39try to use the audio capture function of your card. If the frequency of 40recorded data is not right, try to specify the ``digital_rate`` option with 41other values than the default 32000 (often it's 44100 or 64000). 42 43If you have an unknown card, please mail the ID and board name to 44<alsa-devel@alsa-project.org>, regardless of whether audio capture works 45or not, so that future versions of this driver know about your card. 46 47 48Audio modes 49=========== 50 51The chip knows two different modes (digital/analog). snd-bt87x 52registers two PCM devices, one for each mode. They cannot be used at 53the same time. 54 55 56Digital audio mode 57================== 58 59The first device (hw:X,0) gives you 16 bit stereo sound. The sample 60rate depends on the external source which feeds the Bt87x with digital 61sound via I2S interface. 62 63 64Analog audio mode (A/D) 65======================= 66 67The second device (hw:X,1) gives you 8 or 16 bit mono sound. Supported 68sample rates are between 119466 and 448000 Hz (yes, these numbers are 69that high). If you've set the CONFIG_SND_BT87X_OVERCLOCK option, the 70maximum sample rate is 1792000 Hz, but audio data becomes unusable 71beyond 896000 Hz on my card. 72 73The chip has three analog inputs. Consequently you'll get a mixer 74device to control these. 75 76 77Have fun, 78 79 Clemens 80 81 82Written by Clemens Ladisch <clemens@ladisch.de> 83big parts copied from btaudio.txt by Gerd Knorr <kraxel@bytesex.org> 84