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Encyclopedia > Interrupt

In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. A hardware interrupt causes the processor to save its state of execution via a context switch, and begins execution of an interrupt handler. Software interrupts are usually implemented as instructions in the instruction set, which cause a context switch to the interrupt handler similarly to a hardware interrupt. Interrupts are a commonly used technique for computer multitasking, especially in real-time computing. Such a system is said to be interrupt-driven. Originally, the word computing was synonymous with counting and calculating, and a science and technology that deals with the original sense of computing mathematical calculations. ... An asynchronous circuit is a circuit in which the parts are largely autonomous. ... CPU redirects here. ... A context switch is the computing process of storing and restoring the state (context) of a CPU such that multiple processes can share a single CPU resource. ... An interrupt handler, also known as an interrupt service routine, is a subroutine in an operating system or device driver whose execution is triggered by the reception of an interrupt. ... In computer science, an instruction typically refers to a single operation of a processor within a computer architecture. ... An instruction set, or instruction set architecture (ISA), describes the aspects of a computer architecture visible to a programmer, including the native datatypes, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O (if any). ... In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is...


An act of interrupting is referred to as an interrupt request. In computing, an interrupt request (IRQ) is a phrase used to refer to either the act of interrupting, the bus lines used to signal an interrupt, or the interrupt input lines on a Programmable Interrupt Controller (PIC). ...

Contents

Overview

Interrupts originated as a way to avoid wasting the processor's valuable time in polling loops, waiting for external events. Instead, an interrupt signals the processor when an event occurs, allowing the processor to process other work while the event is pending.


Interrupts are mainly classified into two types:

  1. Synchronous Interrupts
  2. Asynchronous Interrupts

Synchronous interrupts: A synchronous interrupt is one that will be raised by software or a software instance (code snippet) that is known to occur at a particular time when a particular instruction gets executed. This is so called because it is predictable, and only occurs when some part of code gets executed in particular context.


Asynchronous interrupts: An asynchronous interrupt is one that will be raised by a hardware device at some unknown time (may it be frequently or seldom), but is initiated by a hardware device and is unpredictable to the kernel and the user of the instance when a device triggers interrupt and needs attention. Interrupt in general sense means "breaking the flow of" and, as it is not known earlier, an asynchronous interrupt.


Interrupts may be implemented in hardware as a distinct system with control lines, or they may be integrated into the memory subsystem. If implemented in hardware, a Programmable Interrupt Controller (PIC) or Advanced Programmable Interrupt Controller (APIC) is connected to both the interrupting device and to the processor's interrupt pin. If implemented as part of the memory controller, interrupts are mapped into the system's memory address space. A Programmable Interrupt Controller (PIC) is a device which allows priority levels to be assigned to its interrupt outputs. ... An Advanced Programmable Interrupt Controller (APIC) is a more intricate Programmmable Interrupt Controller (PIC). ...


Interrupts can be categorized into the following types: software interrupt, maskable interrupt, non-maskable interrupt (NMI), interprocessor interrupt (IPI), and spurious interrupt. A Non-Maskable Interrupt (NMI) is a special type of interrupt that can not be ignored by standard interrupt masking techniques. ... An Inter-Processor Interrupt (IPC) is a special type of interrupt by which one processor may interrupt another processor in a multiprocessor system. ...

  • A software interrupt is an interrupt generated within a processor by executing an instruction. Examples of software interrupts are system calls.
  • A maskable interrupt is essentially a hardware interrupt which may be ignored by setting a bit in an interrupt mask register's (IMR) bit-mask.
  • Likewise, a non-maskable interrupt is a hardware interrupt which typically does not have a bit-mask associated with it allowing it to be ignored.
  • An interprocessor interrupt is a special type of interrupt which is generated by one processor to interrupt another processor in a multiprocessor system.
  • A spurious interrupt is a hardware interrupt which is generated by system errors, such as electrical noise on one of the PICs interrupt lines.

Processors typically have an internal interrupt mask which allows software to ignore all external hardware interrupts while it is set. This mask may offer faster access than accessing an IMR in a PIC, or disabling interrupts in the device itself. In some cases, such as the x86 architecture, disabling and enabling interrupts on the processor itself acts as a memory barrier, in which case it may actually be slower. In computing, a system call is the mechanism used by an application program to request service from the operating system, or more specifically, the operating system kernel. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... Memory barrier, also known as membar or memory fence is a name for a class of instructions for a computer in computer architecture. ...


The phenomenon where the overall system performance is severely hindered by excessive amounts of processing time spent handling interrupts is called an interrupt storm or live lock. In operating systems, an Interrupt Storm is the generally accepted jargon term for the phenomena where the overall system performance is severely hindered by excessive amounts of processing time spent handling interrupts. ... A deadlock is a situation wherein two or more competing actions are waiting for the other to finish, and thus neither ever does. ...


Typical uses

Typical interrupt uses include the following: system timers, disks I/O, power-off signals, and traps. Other interrupts exist to transfer data bytes using UARTs or Ethernet; sense key-presses; control motors; or anything else the equipment must do. Exception handling is a programming language construct or computer hardware mechanism designed to handle the occurrence of some condition that changes the normal flow of execution. ... A UART or universal asynchronous receiver-transmitter is a piece of computer hardware that translates between parallel bits of data and serial bits. ... Ethernet is a large and diverse family of frame-based computer networking technologies for local area networks (LANs). ...


A classic system timer interrupt interrupts periodically from a counter or the power-line. The interrupt handler counts the interrupts to keep time. The timer interrupt may also be used by the OS's task scheduler to reschedule the priorities of running processes. Counters are popular, but some older computers used the power line frequency instead, because power companies in most Western countries control the power-line frequency with an atomic clock. Scheduling is the process of assigning tasks to a set of resources. ... In computing, a process is a running instance of a program, including all variables and other states. ... Atomic clock Chip-Scale Atomic Clock Unveiled by NIST An atomic clock is a type of clock that uses an atomic resonance frequency standard as its counter. ...


A disk interrupt signals the completion of a data transfer from or to the disk peripheral. A process waiting to read or write a file starts up again.


A power-off interrupt predicts or requests a loss of power. It allows the computer equipment to perform an orderly shutdown.


Interrupts are also used in typeahead features for buffering events like keystrokes. Typeahead is a feature of computers and software (and typewriters, in days gone by) that enables users to continue typing regardless of program or computer operation - the user may type in whatever speed he desires, and if the receiving software is busy at the time it will be called to...


See also

An Advanced Programmable Interrupt Controller (APIC) is a more intricate Programmmable Interrupt Controller (PIC). ... A Programmable Interrupt Controller (PIC) is a device which allows priority levels to be assigned to its interrupt outputs. ... An Inter-Processor Interrupt (IPC) is a special type of interrupt by which one processor may interrupt another processor in a multiprocessor system. ... An interrupt handler, also known as an interrupt service routine, is a subroutine in an operating system or device driver whose execution is triggered by the reception of an interrupt. ... Interrupt latency is the time between the generation of an interrupt by a device and the servicing of the device which generated the interrupt. ... A Non-Maskable Interrupt (NMI) is a special type of interrupt that can not be ignored by standard interrupt masking techniques. ... BIOS Interrupt Calls are a facility that MS-DOS programs, and some other software such as boot loaders, use to invoke the BIOSs facilities. ...

External links

  • Interrupts Made Easy
  • Handling parallel port interrupts from Win32

  Results from FactBites:
 
Interrupt - Wikipedia, the free encyclopedia (752 words)
Software interrupts are usually implemented as instructions in the instruction set, which cause a context switch to the interrupt handler similarly to a hardware interrupt.
Interrupt in general sense means "breaking the flow of" and, as it is not known earlier, an asynchronous interrupt.
Interrupts may be implemented in hardware as a distinct system with control lines, or they may be integrated into the memory subsystem.
Interrupt class Reference (662 words)
We record whether interrupts are enabled or disabled, and any hardware interrupts that are scheduled to occur in the future.
Interrupt::ChangeLevel Change interrupts to be enabled or disabled, without advancing the simulated time (normally, enabling interrupts advances the time).
Interrupt::YieldOnReturn Called from within an interrupt handler, to cause a context switch (for example, on a time slice) in the interrupted thread, when the handler returns.
  More results at FactBites »

 
 

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