| .. SPDX-License-Identifier: GPL-2.0 |
| |
| The bttv driver |
| =============== |
| |
| 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 :doc:`/admin-guide/media/bttv-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`` 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 |
| information 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 http://btwincap.sourceforge.net/download.html. |
| |
| 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 |