1 files changed, 96 insertions, 0 deletions
diff --git a/Documentation/video4linux/bttv/Sound-FAQ b/Documentation/video4linux/bttv/Sound-FAQ
new file mode 100644
index 000000000..ce8895700
--- /dev/null
+++ b/Documentation/video4linux/bttv/Sound-FAQ
@@ -0,0 +1,96 @@
+
+bttv and sound mini howto
+=========================
+
+There are alot 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.c, which holds the informations 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)
+
+You should verify this is correct.  If it is'nt, 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 is'nt listed there, you might check the source code for
+new entries which are not listed yet.  If there is'nt 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 is'nt 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...
+
+
+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.
+
+All 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.
+
+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.  What is in there:
+
+struct tvcard
+{
+        char *name;
+        int inputs;       /* number of video inputs */
+        int tuner;        /*   which of them is the tuner */
+        int svhs;         /*   which of them is the svhs input */
+        u32 gpiomask;
+        u32 muxsel[8];    /* video mux */
+        u32 audiomux[6];  /* audio mux: Tuner, Radio, external, internal, mute, stereo */
+        u32 gpiomask2;    /* GPIO MUX mask (this is video) */
+};
+
+gpiomask has all bits set which are used to control the audio mux.
+This value basically goes to the gpio output enable register.  It is
+also used to mask bits when switching the audio mux (which is done by
+read-modify-write on the gpio data register).
+
+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.  There is
+some #ifdef'ed code in bttv.c (search for "new card") which prints
+these values before board initialization, this might help too: boot
+win, start tv app, softboot (loadlin) into linux and load bttv with
+this enabled.  If you hav'nt Windows installed, this is a trial and
+error game...
+
+Good luck,
+
+  Gerd
+
+
+PS: If you have a new working entry, mail it to me.
+
+-- 
+Gerd Knorr <kraxel@goldbach.in-berlin.de>