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- 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>
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