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Subclassing Protocol Services Drivers

The protocol services driver in the transport driver layer of the mass storage driver stack is responsible for preparing the commands it receives from the logical unit driver for transmission across a particular bus. Each supported bus defines a bus transport protocol that specifies how commands and data are sent across the bus. If your device does not comply with the bus transport protocol of the bus it’s connected to, you need to subclass the appropriate Apple protocol services driver to provide the support your device requires.

Apple provides protocol services drivers for devices that comply with the following bus transport protocols:

• FireWire Serial Bus Protocol 2 specifications (see http://t10.org)

• USB mass storage class specifications (see http://www.usb.org)

• ATA/ATAPI-5 specifications (see http://t13.org)

This chapter describes how to subclass an Apple-provided protocol services driver to address bus-specific issues. The sample code in this chapter is generic and emphasizes the form your driver should take, rather than the code required to implement a specific method. Because the sample driver is generic, it will not attach to a particular device. To test it with your device, you can replace the generic values for parameters such as vendor or product identification with values that identify your device.

The sample code in this chapter is from a Xcode project that builds an I/O Kit driver. For more information on how to develop kernel extensions in general and I/O Kit drivers in particular, see Kernel Extension Programming Topics and I/O Kit Device Driver Design Guidelines.

Contents:

Setting Up Your Project
Creating Your Driver
Testing Your Driver

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