Trying to make a new card entry for BTTV

Hi,

I'm trying to get my Modular Technology PCTV card to give me sound with
bttv0.7.75, and I've run into something I'm not quite understanding.

I've observed that the Windows drivers for this card program
BT848_GPIO_OUT_EN with 00fff000, and that BT848_GPIO_DATA switches
between 00eb0e80 and 00eb0e10.

So I plug these values into bttv as a guess:

insmod bttv bttv_gpio=1
audiomux=0xeb0e80,0xeb0e10,0xeb0e10,0xeb0e10,0xeb0e10 gpiomask=0xfff000

and I find debug messages in my logs saying:

Aug 27 05:18:00 funkster kernel: bttv0: gpio: en=00fff000, out=00eb0000
in=00000f10 [audio: off]
Aug 27 05:18:09 funkster kernel: bttv0: gpio: en=00fff000, out=00eb0000
in=00000f80 [audio: tuner]

As I understand it from the Sound-FAQ and reading the code, in should
be e80 or e10:

[quoting from Sound-FAQ]
in  =   _in_put bits of the data register,
        i.e. BT848_GPIO_DATA & ~BT848_GPIO_OUT_EN

but it's not, as you can see.

The card uses a TDA9874H for audio decoding, which appears to be
compatible with the TDA9875 (the docs from the Philips website seem to
suggest it is, it's detected as a 9875 and the tda9875 driver doesn't
complain at all).  Sometimes, if I rmmod/insmod the tda9875 driver too
many times, or the very unstable windows drivers crash, the chip seems
to lockup and I need a poweroff/poweron cycle of the computer to make
it respond again to bttv's probing.  When this has happened, the in
values are returned correctly in the logs as e80 and e10, but as the
decoder chip is not responding, I still have no sound.  :-)

Is there something strange going on here or have I missed something
really obvious?

-- 
marm