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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
2bttv and sound mini howto
3=========================
4
5There are alot of different bt848/849/878/879 based boards available.
6Making video work often is not a big deal, because this is handled
7completely by the bt8xx chip, which is common on all boards. But
8sound is handled in slightly different ways on each board.
9
10To handle the grabber boards correctly, there is a array tvcards[] in
11bttv-cards.c, which holds the informations required for each board.
12Sound will work only, if the correct entry is used (for video it often
13makes no difference). The bttv driver prints a line to the kernel
14log, telling which card type is used. Like this one:
15
16 bttv0: model: BT848(Hauppauge old) [autodetected]
17
18You should verify this is correct. If it isn't, you have to pass the
19correct board type as insmod argument, "insmod bttv card=2" for
20example. The file CARDLIST has a list of valid arguments for card.
21If your card isn't listed there, you might check the source code for
22new entries which are not listed yet. If there isn't one for your
23card, you can check if one of the existing entries does work for you
24(just trial and error...).
25
26Some boards have an extra processor for sound to do stereo decoding
27and other nice features. The msp34xx chips are used by Hauppauge for
28example. If your board has one, you might have to load a helper
29module like msp3400.o to make sound work. If there isn't one for the
30chip used on your board: Bad luck. Start writing a new one. Well,
31you might want to check the video4linux mailing list archive first...
32
33Of course you need a correctly installed soundcard unless you have the
34speakers connected directly to the grabber board. Hint: check the
35mixer settings too. ALSA for example has everything muted by default.
36
37
38How sound works in detail
39=========================
40
41Still doesn't work? Looks like some driver hacking is required.
42Below is a do-it-yourself description for you.
43
44The bt8xx chips have 32 general purpose pins, and registers to control
45these pins. One register is the output enable register
46(BT848_GPIO_OUT_EN), it says which pins are actively driven by the
47bt848 chip. Another one is the data register (BT848_GPIO_DATA), where
48you can get/set the status if these pins. They can be used for input
49and output.
50
51Most grabber board vendors use these pins to control an external chip
52which does the sound routing. But every board is a little different.
53These pins are also used by some companies to drive remote control
54receiver chips. Some boards use the i2c bus instead of the gpio pins
55to connect the mux chip.
56
57As mentioned above, there is a array which holds the required
58informations for each known board. You basically have to create a new
59line for your board. The important fields are these two:
60
61struct tvcard
62{
63 [ ... ]
Mauro Carvalho Chehab4ac97912005-11-08 21:37:43 -080064 u32 gpiomask;
65 u32 audiomux[6]; /* Tuner, Radio, external, internal, mute, stereo */
Linus Torvalds1da177e2005-04-16 15:20:36 -070066};
67
68gpiomask specifies which pins are used to control the audio mux chip.
69The corresponding bits in the output enable register
70(BT848_GPIO_OUT_EN) will be set as these pins must be driven by the
71bt848 chip.
72
73The audiomux[] array holds the data values for the different inputs
74(i.e. which pins must be high/low for tuner/mute/...). This will be
75written to the data register (BT848_GPIO_DATA) to switch the audio
76mux.
77
78
79What you have to do is figure out the correct values for gpiomask and
80the audiomux array. If you have Windows and the drivers four your
81card installed, you might to check out if you can read these registers
82values used by the windows driver. A tool to do this is available
83from ftp://telepresence.dmem.strath.ac.uk/pub/bt848/winutil, but it
84does'nt work with bt878 boards according to some reports I received.
85Another one with bt878 suport is available from
86http://btwincap.sourceforge.net/Files/btspy2.00.zip
87
88You might also dig around in the *.ini files of the Windows applications.
89You can have a look at the board to see which of the gpio pins are
90connected at all and then start trial-and-error ...
91
92
93Starting with release 0.7.41 bttv has a number of insmod options to
94make the gpio debugging easier:
95
96bttv_gpio=0/1 enable/disable gpio debug messages
97gpiomask=n set the gpiomask value
98audiomux=i,j,... set the values of the audiomux array
99audioall=a set the values of the audiomux array (one
100 value for all array elements, useful to check
101 out which effect the particular value has).
102
103The messages printed with bttv_gpio=1 look like this:
104
105 bttv0: gpio: en=00000027, out=00000024 in=00ffffd8 [audio: off]
106
107en = output _en_able register (BT848_GPIO_OUT_EN)
108out = _out_put bits of the data register (BT848_GPIO_DATA),
109 i.e. BT848_GPIO_DATA & BT848_GPIO_OUT_EN
110in = _in_put bits of the data register,
111 i.e. BT848_GPIO_DATA & ~BT848_GPIO_OUT_EN
112
113
114
115Other elements of the tvcards array
116===================================
117
118If you are trying to make a new card work you might find it useful to
119know what the other elements in the tvcards array are good for:
120
121video_inputs - # of video inputs the card has
122audio_inputs - historical cruft, not used any more.
123tuner - which input is the tuner
124svhs - which input is svhs (all others are labeled composite)
125muxsel - video mux, input->registervalue mapping
126pll - same as pll= insmod option
127tuner_type - same as tuner= insmod option
128*_modulename - hint whenever some card needs this or that audio
Mauro Carvalho Chehab4ac97912005-11-08 21:37:43 -0800129 module loaded to work properly.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700130has_radio - whenever this TV card has a radio tuner.
131no_msp34xx - "1" disables loading of msp3400.o module
Michael Krufky994914e2005-11-08 21:37:28 -0800132no_tda9875 - "1" disables loading of tda9875.o module
133needs_tvaudio - set to "1" to load tvaudio.o module
Linus Torvalds1da177e2005-04-16 15:20:36 -0700134
135If some config item is specified both from the tvcards array and as
136insmod option, the insmod option takes precedence.
137
138
139
140Good luck,
141
142 Gerd
143
144
145PS: If you have a new working entry, mail it to me.
146
Michael Krufky994914e2005-11-08 21:37:28 -0800147--
Linus Torvalds1da177e2005-04-16 15:20:36 -0700148Gerd Knorr <kraxel@bytesex.org>