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14-September-2008 12:50:30 - Device driver In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a 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. Contents 1 Purpose 2 Design 3 Development 4 Kernel-mode vs User-mode 5 Device driver applications 6 Virtual device drivers 7 Open drivers 8 Driver APIs 9 Identifiers 10 See also 11 References 12 External links 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. In Linux, device drivers can be built either as parts of the kernel or separately as loadable modules. Makedev includes a list of the devices in Linux: ttyS terminal, lp parallel port, hd disk, loop loopback disk device, sound these include mixer, sequencer, dsp, and audio... 1 The Windows .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... 2 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. Kernel-mode vs User-mode Device drivers, particularly on modern Windows platforms, can run in kernel-mode Ring 0 or in user-mode 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. 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 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 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 to emulate a hardware device, particularly 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. Virtual devices are also used 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 Mb/sec Ethernet isp: Differential SCSI controllers and the SunSwift card glm: 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+ Driver APIs Main article: API 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 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. Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion. June 2008 See also Class driver Firmware Interrupt Loadable kernel module Makedev Open source hardware Printer driver udev References ^ MAKEDEV - Linux Command - Unix Command ^ Device Driver Basics. ^ User-mode vs. Kernel-mode Drivers. Microsoft 2003-03-01. Retrieved on 2008-03-04. ^ Introduction to the User-Mode Driver Framework UMDF. Microsoft 2006-10-10. Retrieved on 2008-03-04. External links Microsoft Windows Hardware Developer Central 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 Linux-Friendly Hardware Understanding Drivers at HowStuffWorks v d e Operating system General History · Timeline · Developement · List Kernel General Microkernel · Nanokernel Types monolithic · hybrid Components Kernel space · Loadable kernel module · device driver · User space · Userland Process management Process · Multiprogramming · Interrupt · Modes: Protected mode · Supervisor mode · Computer multitasking · Scheduling · Context switch · Cooperative multitasking · Preemptive multitasking · CPU modes · Thread computer science Memory management Memory protection · Segmentation · Paging · Memory management unit · Segmentation fault · General protection fault Examples AmigaOS · BeOS · IBM OS/2 · MS-DOS · Windows · Linux · UNIX · OpenSolaris · Mac OS X · ReactOS · more... Miscellaneous concepts Boot loader · PXE · API · Virtual file system · Virtual tape library · Computer network · GUI · HAL Retrieved from http://en..org/wiki/Device_driver Categories: Device drivers | Operating system technology | Digital electronics | Computer buses | MotherboardHidden categories: Articles to be expanded since June 2008 | All articles to be expanded Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages العربية Bosanski Català Česky Dansk Deutsch Español Esperanto Français Bahasa Indonesia Ã?slenska Italiano עברית Қазақша LatvieÅ¡u Lëtzebuergesch Magyar Nederlands 日本語 ‪Norsk bokmÃ¥l‬ ‪Norsk nynorsk‬ Polski Português Română РуÑ?Ñ?кий Simple English SlovenÄ?ina СрпÑ?ки / Srpski Suomi Svenska Tiếng Việt УкраїнÑ?ька 粵語 ä¸æ–‡ This page was last modified on 11 September 2008, at 10:43
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