Device Dependent Structure (DDS) Overview

A device dependent structure (DDS) contains information that describes a device instance to the device driver. It typically contains information about device-dependent attributes as well as other information the driver needs to communicate with the device.

In many cases, information about a device’s parent is included. (For instance, a driver needs information about the adapter and the bus the adapter is plugged into to communicate with a device connected to an adapter.)

A device's DDS is built each time the device is configured. The Configure method can fill in the DDS with fixed values, computed values, and information from the Configuration database. Most of the information from the Configuration database usually comes from the attributes for the device in the Customized Attribute (CuAt) object class, but can come from any of the object classes. Information from the database for the device's parent device or parent's parent device can also be included. The DDS is passed to the device driver with the SYS_CFGDD flag of the sysconfig subroutine, which calls the device driver's ddconfig subroutine with the CFG_INIT command.