Specifications

D
evice Driver Programming
Glossary-4
device understands. For example, on a disk drive, the controller accepts a request to read a
file and converts the request into hardware commands to have the reading apparatus move
to the precise location and send the information until a delimiter is reached.
critical code
A section of code is critical if execution of arbitrary interrupt handlers could result in con-
sistency problems. The kernel raises the processor execution level to prevent interrupts
during a critical code section.
cyclic redundancy check (CRC)
A way to check the transfer of information over a channel. When the message is received,
the computer calculates the remainder and checks it against the transmitted remainder.
data structure
The memory storage area that holds data types, such as integers and strings, or an array of
integers. The data structures associated with drivers are used as buffers for holding data
being moved between user data space and the device, as flags for indicating error device
status, as pointers to link buffers together, and so on.
data terminal ready (DTR)
The signal that a terminal device sends to a host computer to indicate that a terminal is
ready to receive data.
data transfer
The phase in connection and connectionless modes that supports the transfer of data
between two DLS users.
DDI/DKI
The Device Driver Interface and the Driver-Kernel Interface specify the interactions
between a device driver or STREAMS module and the rest of the UNIX System V kernel.
demand paging
A memory management system that allows unused portions of a program to be stored tem-
porarily on disk to make room for urgently needed information in main memory. With
demand paging, the virtual size of a process can exceed the amount of physical memory
available in a system.
device number
The value used by the operating system to name a device. The device number contains the
major number and the minor number.