Necessary Kernel Drivers

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The kernel drivers that are required to use cameras and video input hardware are quite varied. As a general rule, you need both low-level drivers for your particular hardware or port and Video for Linux drivers. Sometimes the low-level drivers reside in the Video for Linux configuration area, however, and sometimes you don't need the Video for Linux drivers at all. You don't need these drivers to access a digital camera using gPhoto, for instance.

Some of the drivers you might need include

• Video for Linux options The Video for Linux drivers are in a subsection of the Linux kernel configuration off the Character devices option set. Figure 13.6 shows the relevant window in a 2.3.43 kernel. If you're using a 2.2.x kernel, you'll see fewer devices, and if you're using a more recent kernel, you might see more devices. You should select Y or M to the main Video for Linux option, and then select Y or M for your video device. If you have more than one device, you can select them both and use them both, as described later. Even if your device is a USB device without a specific driver in this area, you must enable the main Video for Linux option.

• I2C support In 2.3.x and later kernels, you might need to activate basic I2C support. This support, and various sub-options, are available from the Character devices option list. I2C is a bus developed to link video-related chips, so it's used internally by many video devices.

• USB support If your video device uses a USB interface, you must activate appropriate USB support. I describe these options in more detail in Chapter 16, "Parallel and Serial Ports."

• Parallel and serial support For parallel or serial devices, you should activate appropriate kernel options, as described in Chapter 16, "Parallel and Serial Ports."

Chapter 13

Video For Linux-

Video For Linux

♦ y||vm vn|| Video For Linux

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-v v 1 |v m ♦ n 11 12C on parallel port

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•V y 11 v m ♦ n 11 ADS Cadet AM/FM Tuner

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•V y 11 v m ♦ n AIMSlab RadioTrack (aka RadioReveal) support

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|20f 1 RadioTrack i/o port (0x20f or 0x30f)

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•V y 11 v m ♦ n AIMSlab RadioTrack II support

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J30c RadioTrack II i/o port (0x20c or 0x30c)

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•V y 11 v m ♦ n Aztech/Packard Bell Radio

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|350 Aztech/Packard Bell I/O port (0x350 or 0x358)

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•V y 11 v m ♦ n 11 GemTek Radio Card support

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GemTeki/o port (0x20c, 0x30c, 0x24c or0x34c)

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■v y 11 v m ♦ n 11 Miro PCM20 Radio

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V y ||vr m ♦ n 11 SFIGFMI Radio

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J SF1GFMI I/O port (0x284 or 0x304)

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Figure 13.6

The Video for Linux subsystem includes drivers for many devices.

After you've compiled your kernel, you might need to create appropriate device files for your video devices. This step isn't normally necessary if you're using a digital camera via the serial >A °

o V o port, but it is for most other devices. Possible devices include iA

• USB digital camera If you've got a USB digital camera, you should create a digital m Te camera device file. Consult the documentation for your digital camera driver for details on what device major and minor numbers to use, because these details have changed during the development of the USB drivers, and might change again.

• TV card or WebCam Most Video for Linux devices use the /dev/video device file, which has a device major number of 81 and a minor number of 0. If you have multiple devices, create multiple files (such as /dev/video0 and /dev/video1), and increment the minor number for each additional device. Some Linux distributions ship with these devices predefined.

Note that there's no USB device file per se; instead, USB devices take over device files that are ordinarily used by other systems, or acquire entirely unique device files. Future USB video devices might conceivably require device files other than those I've outlined here, although anything that works through the Video for Linux framework is likely to use /dev/video*.

Part III

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