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Topic: Interrupt latency

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	Interrupt handler - Wikipedia, the free encyclopedia
		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 handlers have a multitude of functions, which vary based on the reason the interrupt was generated and the speed at which the Interrupt Handler completes its task.
		In response to an interrupt, there is a context switch, and the code for the interrupt is loaded and executed.
	en.wikipedia.org /wiki/Interrupt_handler (496 words)

	[No title]
		Interrupts are a critical component of most real-time applications and it is critical that they be acted upon as quickly as possible.
		Knowledge of the worst case interrupt latency of an executive aids the application designer in determining the maximum period of time between the generation of an interrupt and an interrupt handler responding to that interrupt.
		The worst case interrupt latency of an executive is typically defined as the sum of components (1) and (2).
	www.rtems.com /onlinedocs/doc-current/info/c4x.info-2 (2680 words)

	Timing for KADAK AMX RTOS
		Within the AMX environment, KADAK uses the term interrupt latency to refer to the time taken from the leading edge of an external interrupt request signal to the processor to the fetch of the first interrupt service instruction by the processor.
		The longest delays are usually associated with interrupt requests which occur while the processor is executing complex instructions which, for processor reasons, must be allowed to complete (or at least reach some internal state at which the instruction can be resumed) before the interrupt request can be acknowledged.
		Of equal importance to interrupt latency is what KADAK calls handler latency, the time from the processor's first response to an interrupt request signal through to the first useful instruction in the interrupt service procedure.
	www.kadak.com /html/kdkp2609.htm (530 words)

	Programmable Interrupt Controller - Wikipedia, the free encyclopedia
		The IRR specifies which interrupts are pending acknowledgement, and is typically a symbolic register which can not be directly accessed.
		The IMR specifies which interrupts are to be ignored and not acknowledged.
		Interrupt may be edge triggered or level triggered.
	en.wikipedia.org /wiki/Programmable_Interrupt_Controller (347 words)

	LWN: Realtime and interrupt latency
		Scheduling latency is important, but the harder end of the realtime spectrum also places a premium on interrupt latency: how long the system takes to respond to a hardware interrupt.
		That is a different sort of interrupt latency altogether, and one which even general-purpose kernels try to avoid.
		But when interrupt handlers run in their own threads, all that is really needed to avoid concurrency problems is to disable preemption.
	lwn.net /Articles/139784 (1276 words)

	RTC Magazine (Site not responding. Last check: 2007-10-29)
		Interrupt latency is defined as the elapsed time between the occurrence of an interrupt and the execution of the first instruction in the corresponding interrupt service routine (ISR).
		This is generally longer than the interrupt latency, and is important in systems where the response to the external event must involve use of OS services that are only accessible from the task level, not from the ISR level.
		Rather than estimating worst-case interrupt latency by ignoring the amount of time for which interrupts might be disabled, a better approach is not to disable interrupts in the software in the first place.
	www.rtcmagazine.com /home/printthis.php?id=100152 (1487 words)

	Making interrupt design firmware friendly
		Interrupts, from the perspective of the firmware, are asynchronous signals.
		The delay in handling an interrupt, called the interrupt latency, is generally measured from the occurrence of the interrupt until the firmware begins to handle the interrupt.
		If the hardware designer is unsure of the need for an interrupt, he or she should work through the operation of the IC at that point to verify that firmware intervention is needed.
	www.us.design-reuse.com /articles/article4154.html (2235 words)

	LSU EE 4770 Lecture Notes
		As a result of an event, which is of a certain event type, an interrupt is requested; as a result a handler is run.
		Worst-case latency is encountered by e if: : : : :a:t the same time as e: : : : :o:ne or more higher priority events occur: : : : :a:nd all other higher priority events occur before e gets to run.
		This worst-case latency is encountered by e if: The longest-run-time handler at the same strong priority level: : : : :s:tarts to run just before e: : : : :a:nd all higher priority interrupts occur before e's handler starts.
	www.ece.lsu.edu /ee4770/1997/lsli16.html (6905 words)

	EETimes Magazine (Site not responding. Last check: 2007-10-29)
		Interrupt latency is defined as the elapsed time between an interrupt and the execution of the first instruction in the corresponding interrupt service routine.
		Interrupts are typically prioritized (by hardware) and nest; therefore, the latency of the highest priority interrupt is usually examined.
		The major component of worst case interrupt latency is the number and length (in terms of time to execute those instructions) of instructions for which the operating system disables interrupts.
	www.acumeninfo.com /eprints/GreenHills.html?clientId=erights (1583 words)

	Audio I
		Latency effects the overall responsiveness of a DAW’s user interface to input gestures as well the applicability of a DAW for live input monitoring.
		Interrupt latency is a fundamental measure of an operating system’s performance and is not a factor that is open to optimization.
		In reality, the influence of system load on interrupt latency and the scheduler will lead to inconsistent performance (manifested by random audio drop-outs), so in most practical cases the audio latency will be much higher.
	www.cakewalk.com /DevXchange/audio_i.asp (1147 words)

	Interrupt Latency in 80386EX Based System
		Interrupt Latency: The time that elapses before an interrupt request is serviced by the CPU (recognition of the interrupt by the CPU with an interrupt acknowledge cycle).
		Interrupt response time: Time that elapses between the occurrence of an interrupt and the execution of the first instruction of that Interrupt Service Routine (ISR) by the CPU.
		Interrupt Service routine: A simple NULL INTR (For USR case) is shown below with number of clock cycles it would take to execute, assuming a 0Wait state memory (Wc=0), if the code memory has wait state then that should be added appropriately.
	www.intel.com /design/intarch/technote/2153.htm (785 words)

	RTOS Selection Guide - real-time operating system, criteria, latency
		Given these characteristics and the relative priorities of the tasks and interrupts in your system, it is possible to analyze the worst-case performance of the software using a technique such as rate monotonic analysis.
		Interrupt latency is the total length of time from an interrupt signal arriving at the processor to the start of the associated interrupt service routine (ISR).
		Of course, if interrupts are ever disabled (say within a system call), the worst-case interrupt latency increases by the maximum amount of time that they are turned off.
	www.netrino.com /Articles/RTOSes (1185 words)

	OSR's ntdev List: ISR Latency question
		Interrupt latency has been deeply analyzed a number times, and there are papers on the web that give some interesting insights.
		To set the affinity for a specific interrupt vector, the interrupt mask for all processors not in the group are set so that they do not see that interrupt, and that is all there is to it.
		If you (heresy!) run your interrupt on a trap gate instead of on an interrupt gate, you are guaranteed that nobody's going to interrupt you, although of course you may still see your interrupt routine running concurrently on more than one processor.
	www.osronline.com /showThread.cfm?link=21424 (4953 words)

	ARM Technical Support FAQs - How does the interrupt handling latency of the ARM720T compare with ARM7TDMI?
		When comparing interrupt latencies, you need to consider the worst case.
		In both cases, when the interrupt is recognised, the core allows the current instruction to complete.
		In the 720T, you cannot specify that the interrupt routine is placed within the cache - it does not have facilities for lockdown.
	www.arm.com /support/faqip/3710.html (279 words)

	LSU EE 4770 Lecture Notes
		Worst-case latency is encountered by e if: : : : : :at the same time as e: : : : : :one or more higher priority events occur: : : : : :and all other higher priority events occur before e gets to run.
		The names of the event types, their occurrence times, the priorities of their respective interrupts, and the run time of their handlers is listed in the table below.
		As with simulator output appearing above, latency and response times shown are only worst c* *ase for a few events, see title at the head of each run.
	www.ece.lsu.edu /ee4770/1999/lsli16.html (6906 words)

	Interrupt Latency
		Latency as defined by CPU vendors varies from zero (the processor is ready to handle an interrupt RIGHT NOW) to the max time specified.
		Turn interrupts off for even a few C statements and latency might run to hundreds of microseconds, far more that those handful of nanoseconds quoted by CPU vendors.
		Latency is pretty easy to measure; sometimes those measurements will yield surprising and scary results.
	www.ganssle.com /articles/interruptlatency.htm (2171 words)

	kernel - real-time multitasking kernel, embedded realtime kernel
		For some people, the interrupt latency of a kernel is the time it takes before a task responds to an interrupt.
		The worst-case kernel interrupt latency is typically less than that of the processor itself.
		Interrupts are re-enabled as soon as possible to minimize application latency.
	www.smxinfo.com /articles/lsr_art/lsr_art.htm (1516 words)

	FAQ: Is there any information available in Concept on interrupt latency time? (Site not responding. Last check: 2007-10-29)
		interrupt latency time values are expressed in milliseconds.
		The performance of interrupt related instructions is especially critical.
		Using a interval timer interrupt instruction adds about 6% to the scan time of the scheduled ladder logic, this increase does not include the time required to execute the interrupt handler subroutine associated with the interrupt.
	www.modicon.com /85256E74004E079B/all/C881DD7782EB5CA085256F0F00499234!OpenDocument (120 words)

	MontaVista Software - Platform to Innovate (Site not responding. Last check: 2007-10-29)
		Interrupt latency, kernel preemption latency and context switch latency are key benchmarks to demonstrate the real-time performance of Linux kernel.
		Generally the hardware part of the interrupt latency is trivial as compared to the software part, so we simply treat the software part of the interrupt latency as the entire interrupt latency.
		Context Switch Latency is the amount of time required by the kernel scheduler to switch from the current executing process or thread to the next process or thread.
	www.mvista.com /products/realtime_benchmarks.html (429 words)

	CommsDesign - Making interrupt design firmware friendly (Site not responding. Last check: 2007-10-29)
		If there is any way that the hardware could change any of the status related to an interrupt, that status must be latched and held separately for use by firmware.
		Sharing status bits is only useful if the total number of interrupt and status bits required to handle the interrupt is less than the bus width of the system (the purpose of combining the bits is to cut the number of register reads required in the ISR).
		In today's embedded systems, the size of the logic handled by a single IC is so large that a single chip-level interrupt register is often insufficient to handle the multiplicity of interrupt signals generated.
	www.commsdesign.com /showArticle.jhtml?articleID=16505908 (2352 words)

	Reducing Interrupt Latency
		I figured that I really don't need to measure the latency, it is sufficient to count the number of hits in the cache to see if locking has a positive or negative effect on the system.
		Since the entire interrupt handler of OSE is much smaller than 32 kb locking the entire L1 instruction cache is really overkill, but hey, at least now you can measure the interrupt latency on the MPC750 so that day wasn't a complete waste of time.
		The results were pretty good, I didn't expect that the interrupt latency would decrease as much as it did after locking the interrupt handler into the cache.
	www.e.kth.se /~e96_dbu/ex/journal.html (3384 words)

	Stack Computers: 6.5 INTERRUPTS AND MULTI-TASKING (Site not responding. Last check: 2007-10-29)
		The first component is the amount of time that elapses between the time that an interrupt request is received by the processor and the time that the processor takes action to begin processing the interrupt service routine.
		If an interrupt is pending, the address of the streamed instruction is pushed onto the return stack as the address to be executed upon return from the interrupt, and the interrupt is allowed to be processed.
		These interrupts do things such as add a few milliseconds to the time-of-day counter, or copy a byte from an input port to a memory buffer.
	www.ece.cmu.edu /~koopman/stack_computers/sec6_5.html (2133 words)

	Reducing Interrupt Latency (Site not responding. Last check: 2007-10-29)
		The time it takes from that the external unit signals an interrupt to the time it’s handled by the software is called interrupt latency.
		It is clear that the interrupt latency in a system can be shortened by locking parts of code into the cache.
		Another way to improve the interrupt latency is to reduce the longest region where interrupts are disabled in the operating system, device drivers, memory protection system and the application.
	www.e.kth.se /~e96_dbu/ex/description.html (364 words)

	Guide to Realtime Programming
		Understanding the causes of latency and minimizing their effects is a key to successful realtime program design, and is the focus of this chapter.
		A system's interrupt service routine (ISR) latency is the elapsed time from when an interrupt occurs until execution of the first instruction in the interrupt service routine.
		When there are other ISRs of equal or greater interrupt priority level running at the time that the realtime device interrupts, the realtime device ISR is blocked from running until the current ISR is finished.
	www.iso.port.ac.uk /docs/digital_unix_40D/APS33DTE/DOCU_012.HTM (1686 words)

	iqexpand.com (Site not responding. Last check: 2007-10-29)
		Interrupt latency is the guaranteed maximum response time of the system to an electronic event (e.g.
		Computers that control machinery usually need low interrupt latencies, because the machine can't, won't or should not wait.
		Such a scheduler keeps critical pieces of code and data in solid-state RAM and guarantees a minimum amount of CPU time and a maximum interrupt latency.
	computer_architecture.iqexpand.com (1148 words)

	TI C671x Interrupt latency and DSP BIOS (Site not responding. Last check: 2007-10-29)
		This interrupt is late by 5us 5% of the time and sometimes it is late by more than 20us depending on what is going on in the system (and there is a lot of random stuff going on).
		I know it is not another interrupt (I am controlling the BIOS tick interrupt and can see the latency issue happen even thought the timer tick int has finished processing).
		I could do two things as a work around: I could use an NMI for this audio interrupt (by feeding NMI with a skewed version of Left/Right clock), or I could set up the EDMA to be completely autonomous and not require accurate interrupt events at all.
	talkaboutelectronicequipment.com /group/comp.dsp/messages/155708.html (506 words)

	[mythtv] Maybe it is interrupt latency (Site not responding. Last check: 2007-10-29)
		Previous message: [mythtv] Maybe it is interrupt latency
		Would suck to have to get a faster processor just to mitigate > high interrupt latencies when an 1800+ is overkill for the work this > machine needs to do 99% of the time.
		If you think it is a PCI latency issue, search the Myth users archive for subject "PCI/AGP Latency".
	www.mythtv.org /pipermail/mythtv-dev/2005-January/029949.html (402 words)

	Gelato :: Community
		microseconds, and measure the pulse width on the interrupt pin.
		the interrupt is asserted to the time the device driver clears the
		Gelato Central Operations is housed within the Coordinated Science Laboratory (CSL) of the College of Engineering at the University of Illinois at Urbana-Champaign (UIUC).
	www.gelato.org /community/answer_threaded.php?id=1_529 (175 words)

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