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