251:(MMU). In these chips, the execution context of an interrupt handler will be essentially the same as the interrupted program, which typically runs on a small stack of fixed size (memory resources have traditionally been extremely scant at the low end). Nested interrupts are often provided, which exacerbates stack usage. A primary constraint on the interrupt handler in this programming endeavour is to not exceed the available stack in the worst-case condition, requiring the programmer to reason globally about the stack space requirement of every implemented interrupt handler and application task.
398:, since they must maintain a guarantee that execution of specific code will complete within an agreed amount of time. To reduce jitter and to reduce the potential for losing data from masked interrupts, programmers attempt to minimize the execution time of a FLIH, moving as much as possible to the SLIH. With the speed of modern computers, FLIHs may implement all device and platform-dependent handling, and use a SLIH for further platform-independent long-lived handling.
173:, are usually dispatched via a hard-coded table of interrupt vectors, asynchronously to the normal execution stream (as interrupt masking levels permit), often using a separate stack, and automatically entering into a different execution context (privilege level) for the duration of the interrupt handler's execution. In general, hardware interrupts and their handlers are used to handle high-priority conditions that require the interruption of the current code the
258:), this is not normally detected in hardware by chips of this class. If the stack is exceeded into another writable memory area, the handler will typically work as expected, but the application will fail later (sometimes much later) due to the handler's side effect of memory corruption. If the stack is exceeded into a non-writable (or protected) memory area, the failure will usually occur inside the handler itself (generally the easier case to later debug).
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first opportunity, to permit higher priority interrupts to interrupt the current handler. It is also important for the interrupt handler to quell the current interrupt source by some method (often toggling a flag bit of some kind in a peripheral register) so that the current interrupt isn't immediately repeated on handler exit, resulting in an infinite loop.
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a full receive buffer) and then marks the back-half (or second level) for execution in the near future at the appropriate scheduling priority; once invoked, the back-half operates in its own process context with fewer restrictions and completes the handler's logical operation (such as conveying the newly received data to an operating system data queue).
207:. However, interrupt handlers have an unusual execution context, many harsh constraints in time and space, and their intrinsically asynchronous nature makes them notoriously difficult to debug by standard practice (reproducible test cases generally don't exist), thus demanding a specialized skillset—an important subset of
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mishandled edge case not occurring for weeks or months of continuous operation. Formal validation of interrupt handlers is tremendously difficult, while testing typically identifies only the most frequent failure modes, thus subtle, intermittent bugs in interrupt handlers often ship to end customers.
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Exiting an interrupt handler with the interrupt system in exactly the right state under every eventuality can sometimes be an arduous and exacting task, and its mishandling is the source of many serious bugs, of the kind that halt the system completely. These bugs are sometimes intermittent, with the
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A modern practice has evolved to divide hardware interrupt handlers into front-half and back-half elements. The front-half (or first level) receives the initial interrupt in the context of the running process, does the minimal work to restore the hardware to a less urgent condition (such as emptying
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For reasons of performance, the handler will typically be initiated in the memory and execution context of the running process, to which it has no special connection (the interrupt is essentially usurping the running context—process time accounting will often accrue time spent handling interrupts to
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Even in a CPU which supports nested interrupts, a handler is often reached with all interrupts globally masked by a CPU hardware operation. In this architecture, an interrupt handler would normally save the smallest amount of context necessary, and then reset the global interrupt disable flag at the
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configured such that stack overflow is trapped by the MMU, either as a system error (for debugging) or to remap memory to extend the space available. Memory resources at this level of microcontroller are typically far less constrained, so that stacks can be allocated with a generous safety margin.
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In a multitasking system, each thread of execution will typically have its own stack. If no special system stack is provided for interrupts, interrupts will consume stack space from whatever thread of execution is interrupted. These designs usually contain an MMU, and the user stacks are usually
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be overwritten, but never will be if the system operates correctly. It is common to regularly observe corruption of the stack guard with some kind of watch dog mechanism. This will catch the majority of stack overflow conditions at a point in time close to the offending operation.
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Later it was found convenient for software to be able to trigger the same mechanism by means of a software interrupt (a form of synchronous interrupt). Rather than using a hard-coded interrupt dispatch table at the hardware level, software interrupts are often implemented at the
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For many reasons, it is highly desired that the interrupt handler execute as briefly as possible, and it is highly discouraged (or forbidden) for a hardware interrupt to invoke potentially blocking system calls. In a system with multiple execution cores, considerations of
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In systems supporting high thread counts, it is better if the hardware interrupt mechanism switches the stack to a special system stack, so that none of the thread stacks need account for worst-case nested interrupt usage. Tiny CPUs as far back as the 8-bit
299:
issues can arise even with only a single CPU core. (It is not uncommon for a mid-tier microcontroller to lack protection levels and an MMU, but still provide a DMA engine with many channels; in this scenario, many interrupts are typically
401:
FLIHs which service hardware typically mask their associated interrupt (or keep it masked as the case may be) until they complete their execution. An (unusual) FLIH which unmasks its associated interrupt before it completes is called a
383:, and the code for the interrupt is loaded and executed. The job of a FLIH is to quickly service the interrupt, or to record platform-specific critical information which is only available at the time of the interrupt, and
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in the operating system until processor time is available for them to perform processing for the interrupt. SLIHs may have a long-lived execution time, and thus are typically scheduled similarly to threads and processes.
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the interrupted process). However, unlike the interrupted process, the interrupt is usually elevated by a hard-coded CPU mechanism to a privilege level high enough to access hardware resources directly.
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Interrupt handlers have a multitude of functions, which vary based on what triggered the interrupt and the speed at which the interrupt handler completes its task. For example, pressing a key on a
169:
The traditional form of interrupt handler is the hardware interrupt handler. Hardware interrupts arise from electrical conditions or low-level protocols implemented in
200:, triggers interrupts that call interrupt handlers which read the key, or the mouse's position, and copy the associated information into the computer's memory.
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Unlike other event handlers, interrupt handlers are expected to set interrupt flags to appropriate values as part of their core functionality.
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In the writable case, one can implement a sentinel stack guard—a fixed value right beyond the end of the legal stack whose value
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condition. Interrupt handlers are initiated by hardware interrupts, software interrupt instructions, or software
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and some other operating systems used in the past‍—‌interrupt handlers are divided into two parts: the
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In a modern operating system, upon entry the execution context of a hardware interrupt handler is subtle.
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A SLIH completes long interrupt processing tasks similarly to a process. SLIHs either have a dedicated
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thread for each handler, or are executed by a pool of kernel worker threads. These threads sit on a
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by the DMA engine itself, and the associated interrupt handler is expected to tread carefully.)
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in process execution. FLIHs also mask interrupts. Reducing the jitter is most important for
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system, the FLIH also (briefly) masks other interrupts of equal or lesser priority.
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In a low-level microcontroller, the chip might lack protection modes and have no
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A FLIH implements at minimum platform-specific interrupt handling similar to
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Jonathan Corbet; Alessandro Rubini; Greg Kroah-Hartman (January 27, 2005).
534:"The Linux Kernel Module Programming Guide, Chapter 12. Interrupt Handlers"
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the execution of a SLIH for further long-lived interrupt handling.
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211:—of software engineers who engage at the hardware interrupt layer.
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from 1978 have provided separate system and user stack pointers.
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When allocated stack space is exceeded (a condition known as a
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or transitions between protected modes of operation, such as
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are also paramount. If the system provides for hardware
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568:"Linux Device Drivers, Chapter 10. Interrupt Handling"
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203:An interrupt handler is a low-level counterpart of
60:. Unsourced material may be challenged and removed.
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27:Computer systems programming special block code
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406:. Reentrant interrupt handlers might cause a
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312:Divided handlers in modern operating systems
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469:Advanced Programmable Interrupt Controller
379:. In response to an interrupt, there is a
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418:, and so they are usually avoided. In a
120:Learn how and when to remove this message
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316:In several operating systems‍—‌
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58:adding citations to reliable sources
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282:Constraints in time and concurrency
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502:Programmable Interrupt Controller
718:Object-oriented operating system
158:, and are used for implementing
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538:The Linux Documentation Project
350:Second-Level Interrupt Handlers
45:needs additional citations for
728:Supercomputer operating system
364:, and SLIHs are also known as
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1:
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486:Interrupts in 65xx processors
342:First-Level Interrupt Handler
703:Just enough operating system
688:Distributed operating system
366:slow/soft interrupt handlers
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816:User space and kernel space
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437:In Linux, FLIHs are called
404:reentrant interrupt handler
396:real-time operating systems
356:). FLIHs are also known as
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723:Real-time operating system
243:Stack space considerations
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919:Multilevel feedback queue
914:Fixed-priority preemptive
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698:Hobbyist operating system
693:Embedded operating system
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475:Inter-processor interrupt
144:interrupt service routine
962:General protection fault
713:Network operating system
667:User features comparison
370:Deferred Procedure Calls
708:Mobile operating system
441:, and SLIHs are called
362:fast interrupt handlers
358:hard interrupt handlers
811:Loadable kernel module
496:Non-maskable interrupt
464:Interrupt vector table
249:memory management unit
879:Process control block
845:Computer multitasking
683:Disk operating system
1050:Virtual tape library
642:Forensic engineering
54:improve this article
1059:Supporting concepts
1045:Virtual file system
185:level as a form of
142:, also known as an
136:systems programming
69:"Interrupt handler"
982:Segmentation fault
830:Process management
420:priority interrupt
377:interrupt routines
209:system programming
18:Interrupt routines
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972:Memory protection
943:Memory management
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929:Shortest job next
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623:Operating systems
481:Interrupt latency
330:Microsoft Windows
231:Execution context
194:computer keyboard
187:callback function
140:interrupt handler
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16:(Redirected from
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575:O'Reilly Media
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540:. May 18, 2007
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491:IRQL (Windows)
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408:stack overflow
381:context switch
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110:February 2015
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71: –
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65:Find sources:
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55:
49:
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43:This article
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37:
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31:
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1002:file systems
894:Time-sharing
580:February 20,
578:. Retrieved
544:February 20,
542:. Retrieved
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414:by the same
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390:FLIHs cause
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372:in Windows.
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134:In computer
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52:Please help
47:verification
44:
1134:Subroutines
1020:Device file
1010:Boot loader
924:Round-robin
849:Cooperative
785:Rump kernel
775:Multikernel
765:Microkernel
662:Usage share
451:bottom half
447:bottom half
412:preemptions
297:concurrency
1129:Interrupts
1123:Categories
950:protection
906:algorithms
904:Scheduling
853:Preemptive
799:Components
770:Monolithic
637:Comparison
515:References
443:lower half
439:upper half
348:) and the
289:reentrancy
156:exceptions
80:newspapers
1040:Partition
957:Bus error
884:Real-time
864:Interrupt
790:Unikernel
755:Exokernel
431:run queue
302:triggered
175:processor
152:interrupt
1086:Live USB
948:resource
838:Concepts
676:Variants
657:Timeline
508:Red zone
457:See also
385:schedule
338:DESQview
1081:Live CD
1035:Journal
999:access,
997:Storage
874:Process
780:vkernel
647:History
630:General
94:scholar
889:Thread
760:Hybrid
738:Kernel
471:(APIC)
427:kernel
392:jitter
96:
89:
82:
75:
67:
1091:Shell
1030:Inode
571:(PDF)
504:(PIC)
498:(NMI)
477:(IPI)
368:, or
326:macOS
318:Linux
198:mouse
138:, an
101:JSTOR
87:books
652:List
582:2015
546:2015
354:SLIH
346:FLIH
334:z/OS
322:Unix
73:news
1108:PXE
1096:CLI
1076:HAL
1066:API
869:IPC
445:or
360:or
293:DMA
263:can
148:ISR
146:or
56:by
1125::
851:,
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554:^
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523:^
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332:,
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847:(
615:e
608:t
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108:(
98:·
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