In computing, a device driver or software driver is a computer program A computer program is a sequence of instructions written to perform a specified task for a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute the instructions. The same program in its human- allowing higher-level computer programs to interact with a hardware Hardware is a general term for the physical artifacts of a technology. It may also mean the physical components of a computer system, in the form of computer hardware device.

A driver typically communicates with the device through the computer bus In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers or communications subsystem to which the hardware connects. When a calling program invokes a routine In computer science, a subroutine is a portion of code within a larger program, which performs a specific task and is relatively independent of the remaining code 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 An operating system is the software on a computer that manages the way different programs use its hardware, and regulates the ways that a user controls the computer. Operating systems are found on almost any device that contains a computer with multiple programs—from cellular phones and video game consoles to supercomputers and web servers. Some-specific. They usually provide the interrupt In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution handling required for any necessary asynchronous time-dependent hardware interface.

Purpose

A device driver simplifies programming by acting as a translator between a hardware device and the applications or operating systems An operating system is the software on a computer that manages the way different programs use its hardware, and regulates the ways that a user controls the computer. Operating systems are found on almost any device that contains a computer with multiple programs—from cellular phones and video game consoles to supercomputers and web servers. Some that use it. Programmers can write the higher-level application code independently of whatever specific hardware device it will ultimately control, because code and device can interface in a standard way, regardless of the software superstructure or of underlying hardware. Every version of a device, such as a printer In computing, a printer is a peripheral which produces a hard copy of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most newer printers, a USB cable to a computer which serves as a document, requires its own hardware-specific specialized commands. In contrast, most applications utilize devices (such as a file to a printer) by means of high-level device-generic commands such as PRINTLN (print a line). The device-driver accepts these generic high-level commands and breaks them into a series of low-level device-specific commands as required by the device being driven. Furthermore, drivers can provide a level of security as they can run in kernel-mode In computer science, hierarchical protection domains, often called protection rings, are a mechanism to protect data and functionality from faults and malicious behaviour (computer security). This approach is diametrically opposite to that of capability-based security, thereby protecting the operating system from applications running in user-mode.

Design

Device drivers can be abstracted into logical and physical layers The Physical Layer is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY. Logical layers process data for a class of devices such as Ethernet Ethernet is a family of frame-based computer networking technologies for local area networks . The name came from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer ports or disk drives. Physical layers communicate with specific device instances. For example, a serial port In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time . Throughout most of the history of personal computers, data transfer through serial ports connected the computer to devices such as terminals and various peripherals needs to handle standard communication protocols such as XON/XOFF Software flow control is a method of flow control used in computer data links, especially RS-232 serial. It uses special codes, transmitted in-band, over the primary communications channel. These codes are generally called XOFF and XON . Thus, "software flow control" is sometimes called "XON/XOFF flow control". This is in 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 The 16550 UART is an integrated circuit designed for implementing the interface for serial communications. It is frequently used to implement the serial port for IBM PC compatible personal computers, where it is often connected to an RS-232 interface for modems, serial mice, printers, and similar peripherals 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 to the logical layer.

In Linux The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software environments, programmers can build device drivers either as parts of the kernel The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software or separately as loadable modules In computing, a loadable kernel module is an object file that contains code to extend the running kernel, or so-called base kernel, of an operating system. Most current Unix-like systems, and Microsoft Windows, support loadable kernel modules, although they might use a different name for them, such as "kernel extension" ("kext"). Makedev includes a list of the devices in Linux: ttyS (terminal), lp (parallel port A parallel port is a type of interface found on computers for connecting various peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port. The IEEE 1284 standard defines the bi-directional version of the port, which transmits data bits at the same time (in &), hd (disk), loop (loopback disk device In Unix-like operating systems, a loop device, vnd , or lofi (loopback file interface) is a pseudo-device that makes a file accessible as a block device), sound (these include mixer, sequencer A music sequencer is an application or a device designed to play back musical notation. The original kind of sequencer is now known as a step sequencer to distinguish it from the modern kind, which records a musician playing notes, dsp A digital signal processor is a specialized microprocessor with an optimized architecture for the fast operational needs of digital signal processing, and audio)... ^[1]

The Microsoft Windows Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal .sys files and Linux .ko modules contain 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 In computing, a platform describes some sort of hardware architecture and software framework , that allows software to run. Typical platforms include a computer's architecture, operating system, programming languages and related user interface (runtime libraries or graphical user interface) function. Drivers operate in a highly privileged In computing, privilege is defined as the delegation of authority over a computer system. A privilege is a permission to perform an action. Examples of various privileges include the ability to create a file in a directory, or to read or delete a file, access a device, or have read or write permission to a socket for communicating over the environment and can cause disaster if they get things wrong.^[2] In contrast, most user-level software on modern operating systems An operating system is the software on a computer that manages the way different programs use its hardware, and regulates the ways that a user controls the computer. Operating systems are found on almost any device that contains a computer with multiple programs—from cellular phones and video game consoles to supercomputers and web servers. Some can be stopped without greatly affecting the rest of the system. Even drivers executing in user mode A conventional computer operating system usually segregates virtual memory into kernel space and user space. Kernel space is strictly reserved for running the kernel, kernel extensions, and most device drivers. In contrast, user space is the memory area where all user mode applications work and this memory can be swapped out when necessary can crash a system if the device is erroneously programmed. These factors make it more difficult and dangerous to diagnose problems.

Thus the task of writing drivers usually falls to software engineers A software engineer is a person who applies the principles of software engineering to the design, development, testing, and evaluation of the software and systems that make computers or anything containing software, such as computer chips, work who work for hardware-development companies. 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 Manufacturing is the use of machines, tools and labor to make things for use or sale. Also it can be used for selling things. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale. Such'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 and open source Free and open source software, also F/OSS, FOSS, or FLOSS is software that is liberally licensed to grant the right of users to use, study, change, and improve its design through the availability of its source code. This approach has gained both momentum and acceptance as the potential benefits have been increasingly recognized by both individuals operating systems An operating system is the software on a computer that manages the way different programs use its hardware, and regulates the ways that a user controls the computer. Operating systems are found on almost any device that contains a computer with multiple programs—from cellular phones and video game consoles to supercomputers and web servers. Some. 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 Reverse engineering is the process of discovering the technological principles of a device, object or system through analysis of its structure, function and operation. It often involves taking something (e.g., a mechanical device, electronic component, or software program) apart and analyzing its workings in detail to be used in maintenance, or to, this is much more difficult with hardware than it is with software.

Microsoft Microsoft Corporation is a public multinational corporation based in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions. Established on April 4, 1975 to develop and sell BASIC interpreters for the Altair 8800, has attempted to reduce system instability due to poorly written device drivers by creating a new framework for driver development, called Windows Driver Foundation The primary tools that comprise WDF are the Kernel Mode Driver Framework and User Mode Driver Framework (UMDF). These tool kits provide a new, object-oriented, programming model for Windows driver development. The primary goal of the Frameworks is "Conceptual Scalability", that is the characteristics of only requiring a driver developer (WDF). This includes User-Mode Driver Framework (UMDF) that encourages development of certain types of drivers — primarily those that implement a message-based protocol Message passing in computer science, is a form of communication used in parallel computing, object-oriented programming, and interprocess communication. In this model processes or objects can send and receive messages to other processes. By waiting for messages processes can also synchronize 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 Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, Mac OS X has been included with all new Macintosh computer systems. It is the successor to Mac OS 9, the final release of the "classic" Mac OS, which had been Apple's primary operating system since 198 called the I/O Kit The I/O Kit is an open-source framework in the XNU kernel that helps developers code device drivers for Apple's Mac OS X operating system. The I/O Kit framework was originally introduced as part of Apple's Rhapsody operating system that later became Mac OS X, and shared no similarities with either Mac OS 9's device driver framework, or that of BSD.

Kernel-mode vs user-mode

Device drivers, particularly on modern^[update] Windows platforms, can run in kernel-mode CPU modes are operating modes for the central processing unit of some computer architectures that place restrictions on the type and scope of operations that can be performed by certain processes being run by the CPU. This design allows the operating system to run with more privileges than application software (Ring 0 In computer science, hierarchical protection domains, often called protection rings, are a mechanism to protect data and functionality from faults and malicious behaviour (computer security). This approach is diametrically opposite to that of capability-based security) or in user-mode A conventional operating system usually segregates virtual memory into kernel space and user space. Kernel space is strictly reserved for running the kernel, kernel extensions, and some device drivers. In contrast, user space is the memory area where all user mode applications work and this memory can be swapped out when necessary. The term (Ring 3).^[3] The primary benefit of running a driver in user mode is improved stability, since a poorly written user mode device driver cannot crash the system by overwriting kernel memory.^[4] On the other hand, user/kernel-mode transitions usually impose a considerable performance overhead, thereby prohibiting user mode-drivers for low latency and high throughput requirements.

Kernel space can be accessed by user module only through the use of system calls. End user programs like the UNIX shell or other GUI based applications are part of the user space. These applications interact with hardware through kernel supported functions.

Applications

Because of the diversity of modern^[update] hardware Hardware is a general term for the physical artifacts of a technology. It may also mean the physical components of a computer system, in the form of computer hardware and operating systems, drivers operate in many different environments. Drivers may interface An interface in computer science refers to a set of named operations that can be invoked by clients. Interface generally refers to an abstraction that an entity provides of itself to the outside. This separates the methods of external communication from internal operation , and allows it to be internally modified without affecting the way outside with:

• printers In computing, a printer is a peripheral which produces a hard copy of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most newer printers, a USB cable to a computer which serves as a document
• video adapters A video card, video adapter, graphics-accelerator card, display adapter or graphics card is an expansion card whose function is to generate and output images to a display. Many video cards offer added functions, such as accelerated rendering of 3D scenes and 2D graphics, video capture, TV-tuner adapter, MPEG-2/MPEG-4 decoding, FireWire, light pen,
• network cards A network interface controller is a hardware device that handles an interface to a computer network and allows a network-capable device to access that network. The NIC has a ROM chip that contains a unique number, the media access control (MAC) Address burned into it. The MAC address identifies the device uniquely on the LAN. The NIC exists on the
• Sound cards A sound card is a computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs. Typical uses of sound cards include providing the audio component for multimedia applications such as music composition, editing video or audio, presentation, education, and entertainment (
• local buses In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers of various sorts — in particular, for bus mastering In computing, bus mastering is a feature supported by many bus architectures that enables a device connected to the bus to initiate transactions. Also called "First-party DMA", to contrast it with Third-party DMA, the situation where the system DMA controller is actually doing the transfer on modern systems
• low-bandwidth In computer networking and computer science, bandwidth, digital bandwidth, or network bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it I/O In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it. The term can also be used as part of an action; to & buses of various sorts (for pointing devices A pointing device is an input interface that allows a user to input spatial (ie, continuous and multi-dimensional) data to a computer. CAD systems and graphical user interfaces (GUI) allow the user to control and provide data to the computer using physical gestures — point, click, and drag — for example, by moving a hand-held mouse across the 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
• image scanners
• digital cameras

Common levels of abstraction for device drivers include:

• for hardware:
  • interfacing directly
  • writing to or reading from a device control register
  • 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^{[citation needed]}
• 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.^{[citation needed]}

Virtual device drivers

Virtual device drivers represent a particular variant of device drivers. They are used to emulate a hardware device, particularly in virtualization environments, for example when a 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.

Virtual devices may also operate in a non-virtualized environment. For example a virtual network adapter is used with a virtual private network, while a virtual disk device is used with iSCSI.

Open drivers

• Printers: CUPS
• Scanners: SANE
• Video: Vidix, Direct Rendering Infrastructure

Solaris descriptions of commonly-used device drivers

• fas: Fast/wide SCSI controller
• hme: Fast (10/100 Mbit/s) Ethernet
• isp: Differential SCSI controllers and the SunSwift card
• glm: (Gigabaud Link Module^[5]) UltraSCSI controllers
• scsi: Small Computer Serial Interface (SCSI) devices
• sf: soc+ or socal Fiber Channel Arbitrated Loop (FCAL)
• soc: SPARC Storage Array (SSA) controllers
• socal: Serial optical controllers for FCAL (soc+)

APIs

• Advanced Linux Sound Architecture (ALSA) - as of 2009^[update] the standard 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 graphic display driver architecture for Windows Vista
• Windows Driver Foundation (WDF)
• Windows Driver Model (WDM)

Identifiers

• Device id is the device identifier and Vendor id is the vendor identifier.

See also

• Class driver
• Firmware
• Interrupt
• Loadable kernel module
• Makedev
• Open-source hardware
• Printer driver
• udev

References

1. ^ "MAKEDEV — Linux Command — Unix Command". Linux.about.com. 2009-09-11. http://linux.about.com/od/commands/l/blcmdl8_MAKEDEV.htm. Retrieved 2009-09-17.
2. ^ "Device Driver Basics". http://www.linux-tutorial.info/modules.php?name=Tutorial&pageid=255.
3. ^ "User-mode vs. Kernel-mode Drivers". Microsoft. 2003-03-01. http://technet2.microsoft.com/windowsserver/en/library/eb1936c0-e19c-4a17-a1a8-39292e4929a41033.mspx?mfr=true. Retrieved 2008-03-04.
4. ^ "Introduction to the User-Mode Driver Framework (UMDF)". Microsoft. 2006-10-10. http://blogs.msdn.com/iliast/archive/2006/10/10/Introduction-to-the-User_2D00_Mode-Driver-Framework.aspx. Retrieved 2008-03-04.
5. ^ "US Patent 5969841 - Gigabaud link module with received power detect signal". PatentStorm LLC. http://www.patentstorm.us/patents/5969841.html. Retrieved 2009-09-08. "An improved Gigabaud Link Module (GLM) is provided for performing bi-directional data transfers between a host device and a serial transfer medium."

External links

• Microsoft Windows Hardware Developer Central
• Linux Hardware Compatibility Lists and Linux Drivers
• Writing Device Drivers: A Tutorial
• If you wish to have Linux drivers written for your device
• Free Linux Driver Development Questions and Answers
• Linux hardware
• O'Reilly e-book: Linux Device Drivers, Third Edition

Categories: Device drivers | Linux drivers | Operating system technology

See Also:

• Device Driver
• Device Driver
• Device Drivers
• Device Driver: Dictionary
• Device Driver: Encyclopedia

What Links Here:

Recently Viewed Pages:

• Home
• Search Terms
• Computers: Software: Device Drivers: Directory
• Image Scanner: Blogs
• Personal Computer: Dictionary
• Device Driver: Encyclopedia
• Ring (Computer Security): Encyclopedia
• Answers
• Manufacturer: Dictionary
• Communicate: Dictionary

Most Popular Pages:

• TI-89
• Search Terms
• Device Driver: Web Search
• Soft Error: Blogs
• Thread (Computer Science): Auctions
• Domain Details
• Free and Open Source Software
• Wsop
• Image Scanner: Blogs
• Device Driver

Related 'Device Driver' Searches: