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Diffstat (limited to 'kernel/Documentation/video4linux/bttv/Sound-FAQ')
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diff --git a/kernel/Documentation/video4linux/bttv/Sound-FAQ b/kernel/Documentation/video4linux/bttv/Sound-FAQ new file mode 100644 index 000000000..d3f1d7783 --- /dev/null +++ b/kernel/Documentation/video4linux/bttv/Sound-FAQ @@ -0,0 +1,148 @@ + +bttv and sound mini howto +========================= + +There are a lot of different bt848/849/878/879 based boards available. +Making video work often is not a big deal, because this is handled +completely by the bt8xx chip, which is common on all boards. But +sound is handled in slightly different ways on each board. + +To handle the grabber boards correctly, there is a array tvcards[] in +bttv-cards.c, which holds the information required for each board. +Sound will work only, if the correct entry is used (for video it often +makes no difference). The bttv driver prints a line to the kernel +log, telling which card type is used. Like this one: + + bttv0: model: BT848(Hauppauge old) [autodetected] + +You should verify this is correct. If it isn't, you have to pass the +correct board type as insmod argument, "insmod bttv card=2" for +example. The file CARDLIST has a list of valid arguments for card. +If your card isn't listed there, you might check the source code for +new entries which are not listed yet. If there isn't one for your +card, you can check if one of the existing entries does work for you +(just trial and error...). + +Some boards have an extra processor for sound to do stereo decoding +and other nice features. The msp34xx chips are used by Hauppauge for +example. If your board has one, you might have to load a helper +module like msp3400.o to make sound work. If there isn't one for the +chip used on your board: Bad luck. Start writing a new one. Well, +you might want to check the video4linux mailing list archive first... + +Of course you need a correctly installed soundcard unless you have the +speakers connected directly to the grabber board. Hint: check the +mixer settings too. ALSA for example has everything muted by default. + + +How sound works in detail +========================= + +Still doesn't work? Looks like some driver hacking is required. +Below is a do-it-yourself description for you. + +The bt8xx chips have 32 general purpose pins, and registers to control +these pins. One register is the output enable register +(BT848_GPIO_OUT_EN), it says which pins are actively driven by the +bt848 chip. Another one is the data register (BT848_GPIO_DATA), where +you can get/set the status if these pins. They can be used for input +and output. + +Most grabber board vendors use these pins to control an external chip +which does the sound routing. But every board is a little different. +These pins are also used by some companies to drive remote control +receiver chips. Some boards use the i2c bus instead of the gpio pins +to connect the mux chip. + +As mentioned above, there is a array which holds the required +informations for each known board. You basically have to create a new +line for your board. The important fields are these two: + +struct tvcard +{ + [ ... ] + u32 gpiomask; + u32 audiomux[6]; /* Tuner, Radio, external, internal, mute, stereo */ +}; + +gpiomask specifies which pins are used to control the audio mux chip. +The corresponding bits in the output enable register +(BT848_GPIO_OUT_EN) will be set as these pins must be driven by the +bt848 chip. + +The audiomux[] array holds the data values for the different inputs +(i.e. which pins must be high/low for tuner/mute/...). This will be +written to the data register (BT848_GPIO_DATA) to switch the audio +mux. + + +What you have to do is figure out the correct values for gpiomask and +the audiomux array. If you have Windows and the drivers four your +card installed, you might to check out if you can read these registers +values used by the windows driver. A tool to do this is available +from ftp://telepresence.dmem.strath.ac.uk/pub/bt848/winutil, but it +does'nt work with bt878 boards according to some reports I received. +Another one with bt878 support is available from +http://btwincap.sourceforge.net/Files/btspy2.00.zip + +You might also dig around in the *.ini files of the Windows applications. +You can have a look at the board to see which of the gpio pins are +connected at all and then start trial-and-error ... + + +Starting with release 0.7.41 bttv has a number of insmod options to +make the gpio debugging easier: + +bttv_gpio=0/1 enable/disable gpio debug messages +gpiomask=n set the gpiomask value +audiomux=i,j,... set the values of the audiomux array +audioall=a set the values of the audiomux array (one + value for all array elements, useful to check + out which effect the particular value has). + +The messages printed with bttv_gpio=1 look like this: + + bttv0: gpio: en=00000027, out=00000024 in=00ffffd8 [audio: off] + +en = output _en_able register (BT848_GPIO_OUT_EN) +out = _out_put bits of the data register (BT848_GPIO_DATA), + i.e. BT848_GPIO_DATA & BT848_GPIO_OUT_EN +in = _in_put bits of the data register, + i.e. BT848_GPIO_DATA & ~BT848_GPIO_OUT_EN + + + +Other elements of the tvcards array +=================================== + +If you are trying to make a new card work you might find it useful to +know what the other elements in the tvcards array are good for: + +video_inputs - # of video inputs the card has +audio_inputs - historical cruft, not used any more. +tuner - which input is the tuner +svhs - which input is svhs (all others are labeled composite) +muxsel - video mux, input->registervalue mapping +pll - same as pll= insmod option +tuner_type - same as tuner= insmod option +*_modulename - hint whenever some card needs this or that audio + module loaded to work properly. +has_radio - whenever this TV card has a radio tuner. +no_msp34xx - "1" disables loading of msp3400.o module +no_tda9875 - "1" disables loading of tda9875.o module +needs_tvaudio - set to "1" to load tvaudio.o module + +If some config item is specified both from the tvcards array and as +insmod option, the insmod option takes precedence. + + + +Good luck, + + Gerd + + +PS: If you have a new working entry, mail it to me. + +-- +Gerd Knorr <kraxel@bytesex.org> |