Based on kernel version 4.13.3. Page generated on 2017-09-23 13:56 EST.
1 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 compliant, ... 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 <kraxel@bytesex.org>