DDKL Device Driver Kit Library
Acronym Definition
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A device driver, or software driver is a computer program allowing higher-level
computer programs to interact with a computer hardware device.
A driver typically communicates with the device through the computer bus or
communications subsystem to which the hardware is connected. When a calling
program invokes a routine in the driver, the driver issues commands to the
device. Once the device sends data back to the driver, the driver may invoke
routines in the original calling program. Drivers are hardware-dependent and
operating-system-specific. They usually provide the interrupt handling required
for any necessary asynchronous time-dependent hardware interface.
Purpose
A device driver simplifies programming by acting as a translator between a
device and the applications or operating systems that use it. The higher-level
code can be written independently of whatever specific hardware device it may
control. Every version of a device, such as a printer, requires its own
specialized commands. In contrast, most applications access devices (such as
sending a file to a printer) by using high-level, generic commands, such as
PRINTLN. The driver accepts these generic statements and converts them into the
low-level commands required by the device.
Design
Device drivers can be abstracted into logical and physical layers. Logical
layers process data for a class of devices such as ethernet ports or disk
drives. Physical layers communicate with specific device instances. For example,
a serial port needs to handle standard communication protocols such as XON/XOFF
that are common for all serial port hardware. This would be managed by a serial
port logical layer. However, the logical layer needs to communicate with a
particular serial port chip. 16550 UART hardware differs from PL-011. The
physical layer addresses these chip specific variations. Conventionally, OS
requests go to the logical layer first. In turn, the logical layer calls upon
the physical layer to implement OS requests in terms understandable by the
hardware. Inversely, when a hardware device needs to respond to the OS, it uses
the physical layer to speak through the logical layer.
Linux device drivers are built into the OS kernel, and thus get built for the
appropriate bit-width automatically. Provided that sufficient technical
information about the hardware is available, the Linux kernel team will write
the drivers free of charge.[1][2][3] This absolves both hardware vendors and end
users from having to worry about drivers.
Additionally, the device drivers can either be built as parts of the kernel or
can be built separately as loadable modules. The Windows(TM) .sys files and
Linux .ko modules are loadable device drivers. The advantage of loadable device
drivers is that they can be loaded only when necessary and then unloaded, thus
saving kernel memory.
Development
Writing a device driver requires an in-depth understanding of how the hardware
and the software of a given platform function. Drivers "...operate in a highly
privileged environment and can cause disaster if they get things wrong..." [1]
In contrast, most user-level software on modern operating systems can be stopped
without greatly affecting the rest of the system. Even drivers executing in user
mode can crash a system if the device is erroneously programmed. These factors
make it more difficult and dangerous to diagnose problems.
Thus drivers are usually written by software engineers who come from the
companies that develop the hardware. This is because they have better
information than most outsiders about the design of their hardware. Moreover, it
was traditionally considered in the hardware manufacturer's interest to
guarantee that their clients can use their hardware in an optimum way.
Typically, the logical device driver (LDD) is written by the operating system
vendor, while the physical device driver (PDD) is implemented by the device
vendor. But in recent years non-vendors have written numerous device drivers,
mainly for use with free operating systems. In such cases, it is important that
the hardware manufacturer provides information on how the device communicates.
Although this information can instead be learned by reverse engineering, this is
much more difficult with hardware than it is with software.
Microsoft has attempted to reduce system instability due to poorly written
device drivers, by creating a new framework for driver development, called
Windows Driver Foundation (WDF). This includes User-Mode Driver Framework (UMDF)
that encourages development of certain types of drivers - primarily those that
implement a message-based protocol for communicating with their devices - as
user mode drivers. If such drivers malfunction, they do not cause system
instability. The Kernel-Mode Driver Framework (KMDF) model continues to allow
development of kernel-mode device drivers, but attempts to provide standard
implementations of functions that are well known to cause problems, including
cancellation of I/O operations, power management, and plug and play device
support.
Apple has an open-source framework for developing drivers on Mac OS X called the
I/O Kit.
Device driver applications
Because of the diversity of modern hardware and operating systems, many ways
exist in which drivers can be used. Drivers are used for interfacing with:
Printers
Video adapters
Network cards
Sound cards
Local buses of various sorts - in particular, for bus mastering on modern
systems
Low-bandwidth I/O buses of various sorts (for pointing devices such as mice,
keyboards, USB, etc.)
computer storage devices such as hard disk, CD-ROM and floppy disk buses (ATA,
SATA, SCSI)
Implementing support for different file systems
Implementing support for image scanners and digital cameras
Common levels of abstraction for device drivers are
For hardware:
Interfacing directly
Using some higher-level interface (e.g. Video BIOS)
Using another lower-level device driver (e.g. file system drivers using disk
drivers)
Simulating work with hardware, while doing something entirely different
For software:
Allowing the operating system direct access to hardware resources
Implementing only primitives
Implementing an interface for non-driver software (e.g. TWAIN)
Implementing a language, sometimes quite high-level (e.g. PostScript)
Choosing and installing the correct device drivers for given hardware is often a
key component of computer system configuration.
Virtual device drivers
A particular variant of device drivers are virtual device drivers. They are used
in virtualization environments, for example when an MS-DOS program is run on a
Microsoft Windows computer or when a guest operating system is run on, for
example, a Xen host. Instead of enabling the guest operating system to dialog
with hardware, virtual device drivers take the opposite role and emulate a piece
of hardware, so that the guest operating system and its drivers running inside a
virtual machine can have the illusion of accessing real hardware. Attempts by
the guest operating system to access the hardware are routed to the virtual
device driver in the host operating system as e.g. function calls. The virtual
device driver can also send simulated processor-level events like interrupts
into the virtual machine.
Open drivers
Printers: CUPS.
Scanners: SANE.
Video: Vidix
Driver APIs
Advanced Linux Sound Architecture (ALSA) - The standard modern Linux sound
driver interface
I/O Kit - an open-source framework from Apple for developing Mac OS X device
drivers
Installable File System (IFS) - a filesystem API for IBM OS/2 and Microsoft
Windows NT
Network Driver Interface Specification (NDIS) - a standard network card driver
API
Open Data-Link Interface (ODI) - a network card API similar to NDIS
Scanner Access Now Easy (SANE) - a public domain interface to raster image
scanner hardware
Uniform Driver Interface (UDI) - a cross platform driver interface project
Windows Display Driver Model (WDDM) - the new graphic display driver
architecture for Windows Vista
Windows Driver Foundation (WDF)
Windows Driver Model (WDM)
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