117 lines
4.8 KiB
ReStructuredText
117 lines
4.8 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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The bttv driver
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===============
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bttv and sound mini howto
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-------------------------
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There are a lot of different bt848/849/878/879 based boards available.
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Making video work often is not a big deal, because this is handled
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completely by the bt8xx chip, which is common on all boards. But
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sound is handled in slightly different ways on each board.
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To handle the grabber boards correctly, there is a array tvcards[] in
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bttv-cards.c, which holds the information required for each board.
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Sound will work only, if the correct entry is used (for video it often
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makes no difference). The bttv driver prints a line to the kernel
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log, telling which card type is used. Like this one::
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bttv0: model: BT848(Hauppauge old) [autodetected]
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You should verify this is correct. If it isn't, you have to pass the
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correct board type as insmod argument, ``insmod bttv card=2`` for
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example. The file Documentation/admin-guide/media/bttv-cardlist.rst has a list
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of valid arguments for card.
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If your card isn't listed there, you might check the source code for
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new entries which are not listed yet. If there isn't one for your
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card, you can check if one of the existing entries does work for you
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(just trial and error...).
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Some boards have an extra processor for sound to do stereo decoding
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and other nice features. The msp34xx chips are used by Hauppauge for
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example. If your board has one, you might have to load a helper
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module like ``msp3400`` to make sound work. If there isn't one for the
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chip used on your board: Bad luck. Start writing a new one. Well,
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you might want to check the video4linux mailing list archive first...
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Of course you need a correctly installed soundcard unless you have the
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speakers connected directly to the grabber board. Hint: check the
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mixer settings too. ALSA for example has everything muted by default.
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How sound works in detail
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~~~~~~~~~~~~~~~~~~~~~~~~~
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Still doesn't work? Looks like some driver hacking is required.
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Below is a do-it-yourself description for you.
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The bt8xx chips have 32 general purpose pins, and registers to control
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these pins. One register is the output enable register
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(``BT848_GPIO_OUT_EN``), it says which pins are actively driven by the
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bt848 chip. Another one is the data register (``BT848_GPIO_DATA``), where
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you can get/set the status if these pins. They can be used for input
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and output.
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Most grabber board vendors use these pins to control an external chip
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which does the sound routing. But every board is a little different.
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These pins are also used by some companies to drive remote control
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receiver chips. Some boards use the i2c bus instead of the gpio pins
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to connect the mux chip.
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As mentioned above, there is a array which holds the required
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information for each known board. You basically have to create a new
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line for your board. The important fields are these two::
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struct tvcard
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{
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[ ... ]
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u32 gpiomask;
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u32 audiomux[6]; /* Tuner, Radio, external, internal, mute, stereo */
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};
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gpiomask specifies which pins are used to control the audio mux chip.
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The corresponding bits in the output enable register
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(``BT848_GPIO_OUT_EN``) will be set as these pins must be driven by the
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bt848 chip.
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The ``audiomux[]`` array holds the data values for the different inputs
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(i.e. which pins must be high/low for tuner/mute/...). This will be
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written to the data register (``BT848_GPIO_DATA``) to switch the audio
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mux.
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What you have to do is figure out the correct values for gpiomask and
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the audiomux array. If you have Windows and the drivers four your
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card installed, you might to check out if you can read these registers
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values used by the windows driver. A tool to do this is available
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from http://btwincap.sourceforge.net/download.html.
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You might also dig around in the ``*.ini`` files of the Windows applications.
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You can have a look at the board to see which of the gpio pins are
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connected at all and then start trial-and-error ...
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Starting with release 0.7.41 bttv has a number of insmod options to
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make the gpio debugging easier:
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================= ==============================================
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bttv_gpio=0/1 enable/disable gpio debug messages
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gpiomask=n set the gpiomask value
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audiomux=i,j,... set the values of the audiomux array
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audioall=a set the values of the audiomux array (one
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value for all array elements, useful to check
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out which effect the particular value has).
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================= ==============================================
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The messages printed with ``bttv_gpio=1`` look like this::
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bttv0: gpio: en=00000027, out=00000024 in=00ffffd8 [audio: off]
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en = output _en_able register (BT848_GPIO_OUT_EN)
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out = _out_put bits of the data register (BT848_GPIO_DATA),
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i.e. BT848_GPIO_DATA & BT848_GPIO_OUT_EN
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in = _in_put bits of the data register,
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i.e. BT848_GPIO_DATA & ~BT848_GPIO_OUT_EN
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