BT878 GPIO programming — Video for Linux

Hi,

I'm having problems controlling the GPIO pins on a BT878 for output.  I'm
measuring the voltage on the GPIO pins and they all remain at 5V ( /0 ).
Are my btwrites() ok????

I've added "audio_hook=external_muxsel" the card entry in struct
bttv_tvcards and this is the external_muxsel():

/* from bttv-cards.c */

static void external_muxsel(struct bttv *btv, struct video_audio *v, int set){

  /* read current GPIO status and print it */
  bttv_gpio_tracking(btv,"pre:external_muxsel");

  /* process GPIO stuff */
  /* NOTE: GPIO_OUT_EN is the output mask register,output=~mask&data */
  /* NOTE: GPIO_DATA is the 24bit input/ouput register */

  btwrite(0x7fff,BT848_GPIO_OUT_EN); // disable all outputs
  btwrite(0x0000,BT848_GPIO_OUT_EN); // enable all outputs
  btwrite(0x0000,BT848_GPIO_DATA); // set all outputs to /0 (+5V)
  btwrite(0x7fff,BT848_GPIO_DATA); // set all outputs to /1 (0V)

  /* read current GPIO status and print it */
  bttv_gpio_tracking(btv,"post:external_muxsel");

}