1.. SPDX-License-Identifier: GPL-2.0
2
3The bttv driver
4===============
5
6bttv and sound mini howto
7-------------------------
8
9There are a lot of different bt848/849/878/879 based boards available.
10Making video work often is not a big deal, because this is handled
11completely by the bt8xx chip, which is common on all boards.  But
12sound is handled in slightly different ways on each board.
13
14To handle the grabber boards correctly, there is a array tvcards[] in
15bttv-cards.c, which holds the information required for each board.
16Sound will work only, if the correct entry is used (for video it often
17makes no difference).  The bttv driver prints a line to the kernel
18log, telling which card type is used.  Like this one::
19
20	bttv0: model: BT848(Hauppauge old) [autodetected]
21
22You should verify this is correct.  If it isn't, you have to pass the
23correct board type as insmod argument, ``insmod bttv card=2`` for
24example.  The file :doc:`/admin-guide/media/bttv-cardlist` has a list
25of valid arguments for card.
26
27If your card isn't listed there, you might check the source code for
28new entries which are not listed yet.  If there isn't one for your
29card, you can check if one of the existing entries does work for you
30(just trial and error...).
31
32Some boards have an extra processor for sound to do stereo decoding
33and other nice features.  The msp34xx chips are used by Hauppauge for
34example.  If your board has one, you might have to load a helper
35module like ``msp3400`` to make sound work.  If there isn't one for the
36chip used on your board:  Bad luck.  Start writing a new one.  Well,
37you might want to check the video4linux mailing list archive first...
38
39Of course you need a correctly installed soundcard unless you have the
40speakers connected directly to the grabber board.  Hint: check the
41mixer settings too.  ALSA for example has everything muted by default.
42
43
44How sound works in detail
45~~~~~~~~~~~~~~~~~~~~~~~~~
46
47Still doesn't work?  Looks like some driver hacking is required.
48Below is a do-it-yourself description for you.
49
50The bt8xx chips have 32 general purpose pins, and registers to control
51these pins.  One register is the output enable register
52(``BT848_GPIO_OUT_EN``), it says which pins are actively driven by the
53bt848 chip.  Another one is the data register (``BT848_GPIO_DATA``), where
54you can get/set the status if these pins.  They can be used for input
55and output.
56
57Most grabber board vendors use these pins to control an external chip
58which does the sound routing.  But every board is a little different.
59These pins are also used by some companies to drive remote control
60receiver chips.  Some boards use the i2c bus instead of the gpio pins
61to connect the mux chip.
62
63As mentioned above, there is a array which holds the required
64information for each known board.  You basically have to create a new
65line for your board.  The important fields are these two::
66
67  struct tvcard
68  {
69	[ ... ]
70	u32 gpiomask;
71	u32 audiomux[6]; /* Tuner, Radio, external, internal, mute, stereo */
72  };
73
74gpiomask specifies which pins are used to control the audio mux chip.
75The corresponding bits in the output enable register
76(``BT848_GPIO_OUT_EN``) will be set as these pins must be driven by the
77bt848 chip.
78
79The ``audiomux[]`` array holds the data values for the different inputs
80(i.e. which pins must be high/low for tuner/mute/...).  This will be
81written to the data register (``BT848_GPIO_DATA``) to switch the audio
82mux.
83
84
85What you have to do is figure out the correct values for gpiomask and
86the audiomux array.  If you have Windows and the drivers four your
87card installed, you might to check out if you can read these registers
88values used by the windows driver.  A tool to do this is available
89from http://btwincap.sourceforge.net/download.html.
90
91You might also dig around in the ``*.ini`` files of the Windows applications.
92You can have a look at the board to see which of the gpio pins are
93connected at all and then start trial-and-error ...
94
95
96Starting with release 0.7.41 bttv has a number of insmod options to
97make the gpio debugging easier:
98
99	=================	==============================================
100	bttv_gpio=0/1		enable/disable gpio debug messages
101	gpiomask=n		set the gpiomask value
102	audiomux=i,j,...	set the values of the audiomux array
103	audioall=a		set the values of the audiomux array (one
104				value for all array elements, useful to check
105				out which effect the particular value has).
106	=================	==============================================
107
108The messages printed with ``bttv_gpio=1`` look like this::
109
110	bttv0: gpio: en=00000027, out=00000024 in=00ffffd8 [audio: off]
111
112	en  =	output _en_able register (BT848_GPIO_OUT_EN)
113	out =	_out_put bits of the data register (BT848_GPIO_DATA),
114		i.e. BT848_GPIO_DATA & BT848_GPIO_OUT_EN
115	in  = 	_in_put bits of the data register,
116		i.e. BT848_GPIO_DATA & ~BT848_GPIO_OUT_EN
117