3. Enabling Support for Your Bt8x8 Hardware in Linux

3.1.1. Module or In-Kernel?

It is likely the stock kernel that was installed on your Linux system, if unmodified, already supports Bt8x8-based hardware. The driver will exist either as a loadable module or within the already running kernel. An easy way to tell is to use the dmesg command piped into less (for easy viewing) to look for an acknowledgement that the driver in question was loaded when your system started up:

   $ dmesg | less

...which may yield something like the following, depending on your exact Bt8x8 chipset features and kernel version (in this case, 2.6):

   Jan 26 19:40:04 localhost kernel: bttv: driver version 0.9.15 loaded
   Jan 26 19:40:04 localhost kernel: bttv: using 8 buffers with 2080k 
      (520 pages) each for capture
   Jan 26 19:40:04 localhost kernel: bttv: Bt8xx card found (0).
   Jan 26 19:40:04 localhost kernel: ACPI: PCI interrupt 0000:02:09.0[A] -> 
      GSI 17 (level, low) -> IRQ 17
   Jan 26 19:40:04 localhost kernel: bttv0: Bt878 (rev 2) at 0000:02:09.0, 
      irq: 17, latency: 32, mmio: 0xe7000000
   Jan 26 19:40:04 localhost kernel: bttv0: detected: Hauppauge WinTV 
      [card=10], PCI subsystem ID is 0070:13eb
   Jan 26 19:40:04 localhost kernel: bttv0: using: Hauppauge (bt878) [card=10, 
      autodetected]
   Jan 26 19:40:04 localhost kernel: bttv0: using tuner=2
   Jan 26 19:40:04 localhost kernel: tuner: chip found at addr 0xc2 i2c-bus 
      bt878 #0 [sw]
   Jan 26 19:40:04 localhost kernel: tuner: type set to 2 (Philips NTSC 
      (FI1236, FM1236 and compatibles)) by bt878 #0 [sw]

If you don't see it, the particular driver module you are interested in may be available but not necessarily loaded at that time. If you know what the module is named, try using find; in this example we are looking for the 'bttv' module:

   $ find /lib/modules -name bttv.o

Note that up until the 2.4 series modules had the suffix .o; for 2.6+ series kernels this was replaced with .ko.

You can get a list of all modules available by typing the following at the command line:

 
   $ ls -R /lib/modules/`uname -r`/kernel 

Where `uname -r`, surrounded by forward tick marks, is your kernel version number. The following output is an example of what you might find in a Bttv-ready kernel, where everything is loaded as a module (edited for brevity):

   /lib/modules/2.6.8/kernel/drivers/media/video:
    btcx-risc.ko    ir-kbd-i2c.ko  tda9875.ko  tvaudio.ko      video-buf.ko
    bttv.ko         msp3400.ko     tda9887.ko  v4l1-compat.ko  videodev.ko
    ir-kbd-gpio.ko  tda7432.ko     tuner.ko    v4l2-common.ko

Again, your output may vary by the currently running kernel capabilities.

Once you know which module your hardware needs you can find out if it is already loaded by typing at the command line or in a terminal window:

   # lsmod

As shown by the prompt above, you will need to have root privileges to do this. You should get output similar to, but not necessarily limited to the following:

   snd_bt87x              11400  0
   tuner                  18832  0
   tvaudio                20428  0
   msp3400                22100  0
   bttv                  145804  0
   video_buf              17476  1 bttv
   i2c_algo_bit            8904  1 bttv
   v4l2_common             4928  1 bttv
   videodev                7232  2 quickcam,bttv

Most stock kernels are compiled with kmod, which enables automatic loading of necessary modules when the appropriate hardware is detected. It may not always do so, however, so if you don't have the particular module you're seeking loaded and you think the module may be available, try loading it manually with modprobe, as in the following example (using the bttv module):

   # modprobe -v bttv

3.3.1. Device Files

If you are using Device Filesystem (devfs) or udev your work in this respect may be done for you dynamically, but at the same time the devices may not exist until they are recognized by the kernel (i.e., the necessary modules loaded), so be sure you have taken care of the previously outlined prerequisites first.

The Linux kernel requires a virtual device node be created to access and control a particular piece of hardware. This node may have already been created for you automatically; ls -l /dev/video* (with an asterisk) or alternatively find /dev -name video* or even visual inspection of the /dev directory with your favorite file manager can give you an idea if the video devices exist. If so you can proceed to Section 3.4; if not you will need to create them manually.

An easy way to create them, if available with your Linux distribution, is use of the MAKEDEV script, which may be located in /dev or the usual places for storing executable commands (/bin,/sbin and so on). The manual page for MAKEDEV (man MAKEDEV) can guide you further, but be aware of the device-specific command options. If MAKEDEV doesn't work or doesn't exist, or you just prefer doing things the hard way, move on to the next paragraph.

A device can be created as a block (such as a drive), a FIFO (file-in-file-out or pipe, as in xconsole) or a character device, which represents other hardware. Each device has a major and a minor number "coordinate" to tell the kernel what it is and where to access it. These numbers are not arbitrary. The major number 81 with minor number 0, 1, 2, and so on are by convention assigned to Video4linux devices, including TV tuner boards and webcams. In order to create the video device /dev/video0, use mknod at the command line:

   # mknod /dev/video0 c 81 0

where c represents a character device.

You can use the following script, which I have borrowed from the kernel source (located in linux/Documentation/video4linux/bttv/MAKEDEV of the source tree):

   #!/bin/bash
   function makedev () {
	for dev in 0 1 2 3; do echo "/dev/$1$dev:
	char 81 $[ $2 + $dev ]" rm -f /dev/$1$dev
	mknod /dev/$1$dev c 81 $[ $2 + $dev ] chmod
	666 /dev/$1$dev
   	done

   	# symlink for default device
	rm -f /dev/$1 ln -s /dev/${1}0 /dev/$1
   	}

	# see http://roadrunner.swansea.uk.linux.org/v4lapi.shtml
	echo "*** new device names ***" makedev video
	0 makedev radio 64 makedev vtx 192 makedev vbi 224
	# "*** old device names (for compatibility only) ***"
	#makedev bttv 0 #makedev bttv-fm 64 #makedev bttv-vbi 224

Simply copy and paste the above into your favorite editing program, save it as MAKEDEV or whatever name you like, make it executable (i.e., chmod u+x MAKEDEV), and then execute it as root:

   # ./MAKEDEV