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Devices Without I/O Kit Families

Some categories of devices do not have family support from I/O Kit. In general, there are three reasons why a particular device may not be supported by an I/O Kit family.

• Support for certain devices is provided by other frameworks. The I/O Kit is not the most appropriate place for the abstractions that represent these devices. Examples of such devices include printers, scanners, digital cameras, and other imaging devices. If you are developing a driver for this category of device, you should use the appropriate imaging SDK.

• For some devices, it is not possible to provide a set of useful, common abstractions. Such devices might include USB security dongles, data acquisition cards, and other vendor-specific devices. These devices do not share a sufficiently large number of characteristics to make creation of I/O Kit families worthwhile. For example, although security dongles all connect via USB, there is no easily defined set of abstractions common to all such devices. An I/O Kit family would not provide substantial assistance to developers. It should not be assumed, however, that a family is required to write a new driver. In many cases, the IOService class provides everything a driver requires to write a “family-less” driver.

• For many devices, it is possible to define a set of useful abstractions; however, Apple has not chosen to create a family for one or more reasons. These devices may be part of a technology that is not a common Macintosh market. Or, Apple’s engineers may not have sufficient in-house expertise with certain devices to create the best family definition. In these cases, an opportunity exists for third-party developers to extend the I/O Kit model by developing families of their own. In addition, families developed under the Apple Public Source License can be sent back to Apple for possible inclusion in future releases of Mac OS X.

In this section:

Imaging Devices
Digital Video
Sequential Access Devices (Tape Drives)
Telephony Devices
Vendor-Specific Devices

Imaging Devices

There is no I/O Kit family for imaging devices (cameras, printers, and scanners). Instead, support for particular imaging device characteristics is handled by user-space code (see “Controlling Devices From Outside the Kernel” for further discussion). Developers who need to support imaging devices should employ the appropriate imaging SDK.

Digital Video

To add digital video capabilities to your software, use the QuickTime APIs.

Sequential Access Devices (Tape Drives)

There is, at present, no I/O Kit family specifically designed for sequential access devices, such as tape drives. However, third-party developers can use the SAM device interface to create plug-in components for such devices.

Telephony Devices

There is, at present, no I/O Kit family for telephony devices. Apple is evaluating plans for a Telephony family for the future.

Vendor-Specific Devices

For some devices, it is not possible to provide a set of useful, common abstractions. Because families define the set of abstractions shared by all devices within the family, it is not feasible to create a family for these devices.

In most cases, however, a family is not necessary in order to write a driver for these devices. Developers should start by inheriting functionality from IOService, then use the GetProperty and SetProperty calls to communicate with their driver. In many cases, this should suffice. In some cases, however, such as data acquisition cards requiring high bandwidth, the developer should create their own user client (for a device-interface plug-in). Such objects can provide shared memory and procedure-call interfaces to a user-space library (see IOUserClient.h). You can find several good examples in IOKitExamples on the Darwin Open Source site.

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