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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

1	
2	bttv and sound mini howto
3	=========================
4	
5	There are a lot of different bt848/849/878/879 based boards available.
6	Making video work often is not a big deal, because this is handled
7	completely by the bt8xx chip, which is common on all boards.  But
8	sound is handled in slightly different ways on each board.
9	
10	To handle the grabber boards correctly, there is a array tvcards[] in
11	bttv-cards.c, which holds the information required for each board.
12	Sound will work only, if the correct entry is used (for video it often
13	makes no difference).  The bttv driver prints a line to the kernel
14	log, telling which card type is used.  Like this one:
15	
16		bttv0: model: BT848(Hauppauge old) [autodetected]
17	
18	You should verify this is correct.  If it isn't, you have to pass the
19	correct board type as insmod argument, "insmod bttv card=2" for
20	example.  The file CARDLIST has a list of valid arguments for card.
21	If your card isn't listed there, you might check the source code for
22	new entries which are not listed yet.  If there isn't one for your
23	card, you can check if one of the existing entries does work for you
24	(just trial and error...).
25	
26	Some boards have an extra processor for sound to do stereo decoding
27	and other nice features.  The msp34xx chips are used by Hauppauge for
28	example.  If your board has one, you might have to load a helper
29	module like msp3400.o to make sound work.  If there isn't one for the
30	chip used on your board:  Bad luck.  Start writing a new one.  Well,
31	you might want to check the video4linux mailing list archive first...
32	
33	Of course you need a correctly installed soundcard unless you have the
34	speakers connected directly to the grabber board.  Hint: check the
35	mixer settings too.  ALSA for example has everything muted by default.
36	
37	
38	How sound works in detail
39	=========================
40	
41	Still doesn't work?  Looks like some driver hacking is required.
42	Below is a do-it-yourself description for you.
43	
44	The bt8xx chips have 32 general purpose pins, and registers to control
45	these pins.  One register is the output enable register
46	(BT848_GPIO_OUT_EN), it says which pins are actively driven by the
47	bt848 chip.  Another one is the data register (BT848_GPIO_DATA), where
48	you can get/set the status if these pins.  They can be used for input
49	and output.
50	
51	Most grabber board vendors use these pins to control an external chip
52	which does the sound routing.  But every board is a little different.
53	These pins are also used by some companies to drive remote control
54	receiver chips.  Some boards use the i2c bus instead of the gpio pins
55	to connect the mux chip.
56	
57	As mentioned above, there is a array which holds the required
58	informations for each known board.  You basically have to create a new
59	line for your board.  The important fields are these two:
60	
61	struct tvcard
62	{
63		[ ... ]
64		u32 gpiomask;
65		u32 audiomux[6]; /* Tuner, Radio, external, internal, mute, stereo */
66	};
67	
68	gpiomask specifies which pins are used to control the audio mux chip.
69	The corresponding bits in the output enable register
70	(BT848_GPIO_OUT_EN) will be set as these pins must be driven by the
71	bt848 chip.
72	
73	The 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
75	written to the data register (BT848_GPIO_DATA) to switch the audio
76	mux.
77	
78	
79	What you have to do is figure out the correct values for gpiomask and
80	the audiomux array.  If you have Windows and the drivers four your
81	card installed, you might to check out if you can read these registers
82	values used by the windows driver.  A tool to do this is available
83	from ftp://telepresence.dmem.strath.ac.uk/pub/bt848/winutil, but it
84	does'nt work with bt878 boards according to some reports I received.
85	Another one with bt878 support is available from
86	http://btwincap.sourceforge.net/Files/btspy2.00.zip
87	
88	You might also dig around in the *.ini files of the Windows applications.
89	You can have a look at the board to see which of the gpio pins are
90	connected at all and then start trial-and-error ...
91	
92	
93	Starting with release 0.7.41 bttv has a number of insmod options to
94	make the gpio debugging easier:
95	
96	bttv_gpio=0/1		enable/disable gpio debug messages
97	gpiomask=n		set the gpiomask value
98	audiomux=i,j,...	set the values of the audiomux array
99	audioall=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	
103	The messages printed with bttv_gpio=1 look like this:
104	
105		bttv0: gpio: en=00000027, out=00000024 in=00ffffd8 [audio: off]
106	
107	en  =	output _en_able register (BT848_GPIO_OUT_EN)
108	out =	_out_put bits of the data register (BT848_GPIO_DATA),
109		i.e. BT848_GPIO_DATA & BT848_GPIO_OUT_EN
110	in  = 	_in_put bits of the data register,
111		i.e. BT848_GPIO_DATA & ~BT848_GPIO_OUT_EN
112	
113	
114	
115	Other elements of the tvcards array
116	===================================
117	
118	If you are trying to make a new card work you might find it useful to
119	know what the other elements in the tvcards array are good for:
120	
121	video_inputs    - # of video inputs the card has
122	audio_inputs    - historical cruft, not used any more.
123	tuner           - which input is the tuner
124	svhs            - which input is svhs (all others are labeled composite)
125	muxsel          - video mux, input->registervalue mapping
126	pll             - same as pll= insmod option
127	tuner_type      - same as tuner= insmod option
128	*_modulename    - hint whenever some card needs this or that audio
129			  module loaded to work properly.
130	has_radio	- whenever this TV card has a radio tuner.
131	no_msp34xx	- "1" disables loading of msp3400.o module
132	no_tda9875	- "1" disables loading of tda9875.o module
133	needs_tvaudio	- set to "1" to load tvaudio.o module
134	
135	If some config item is specified both from the tvcards array and as
136	insmod option, the insmod option takes precedence.
137	
138	
139	
140	Good luck,
141	
142	  Gerd
143	
144	
145	PS: If you have a new working entry, mail it to me.
146	
147	--
148	Gerd Knorr <kraxel@bytesex.org>
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