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1. Top results related to can interrupt latency be calculated from instruction times?

   • Can software interrupt `int` instruction be used to trigger a hardware interrupt handler?

     Top Answer

     Answered Oct 20, 2022 · 2 votes

     In the Intel IA-32 and x86-64 architectures, the Interrupt Descriptor Table (IDT) has a Descriptor privilege level (DPL) field for each entry, which defines the CPU Privilege Levels (CPL) that are allowed to access that interrupt handler via the INT instruction (software interrupts). Hardware interrupts coming from devices ignore this mechanism.

     The Linux operating system kernel initializes all the entries of the IDT while initializing the system. (I presume other operating systems do the same in their own fashion.)

     The INT instruction allows a User Mode process to issue an interrupt signal that has an arbitrary vector ranging from 0 to 255. Therefore, initialization of the IDT must be done carefully, to block illegal interrupts and exceptions simulated by User Mode processes via INT instructions. This can be achieved by setting the DPL field of the IDT entry to 0 (this is ring 0, i.e. kernel mode). If the process attempts to issue one of these interrupt signals, the control unit checks the CPL value against the DPL field and issues a General Protection Fault (interrupt vector number 13).

     In a few cases, however, a User Mode process needs to be able to issue a programmed exception. To allow this, it is sufficient to set the DPL field of the corresponding IDT entry to 3 (ring 3, i.e. userspace). The four Linux exception handlers associated with the vectors 3, 4, 5, and 128 can be issued in User Mode because their IDT entries have the DPL field set to 3. Therefore, the four assembly language instructions INT3 (Breakpoint: interrupt number 3), INTO (Overflow: interrupt number 4), BOUND (Bounds range exceeded: INT 0x05), and INT 0x80 (for system calls) can be issued by User Mode processes.

     The interrupt handlers for all other vectors are privileged and their corresponding INT instructions are considered privileged instructions that can only be executed by the kernel itself, running with CPL 0. What I'm not sure of is whether, in practice, the kernel itself executes INT instructions to call various interrupt handlers.

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     1/5

   • Can SharePoint column be changed from date/time to calculated date/time

     Top Answer

     Answered Apr 13, 2010 · 2 votes

     In the case of a DateTime field, the "calculated" default value is primarily for things like =Today+1. You cannot reference other fields, unfortunately, really the only thing you can reference as a variable is Today. In order to reference a field in a calculation, you would need to use a Calculated field type configured to display a DateTime, instead of a DateTime field type. Unfortunately you cannot convert an existing DateTime field into a Calculated field, so you would have to create a new field.

     If you wanted to play in the object model, though, you could always use a workflow or event handler. I think a SharePoint Designer workflow could also do the trick, if you went that route.

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     2/5

   • Can calculated column be used in another calculated column?

     Top Answer

     Answered Nov 08, 2009 · 1 votes

     To reference pre-calculate a value in SQL usually means performing the calculation in an inner query (AKA inline view):

     SELECT x.exchangerateprice, x.OriginalPriceInDB, 10 * x.exchangerateprice AS CalculatedPrice, x.currencyid FROM (SELECT CASE WHEN pp.price IS NULL THEN 0 WHEN c.CurrencyId = 1 THEN pp.Price ELSE CONVERT(DECIMAL(9, 2), (pp.Price * c.ExchangeRate)) END AS ExchangeRatePrice, price as OriginalPriceInDB, c.currencyid as Currency FROM PRODUCTPRICE pp, CURRENCY c) x

     This is the equivalent to using the WITH clause (available in SQL Server 2005+) - there's no difference in performance.

     You could duplicate the logic:

     SELECT CASE WHEN pp.price IS NULL THEN 0 WHEN c.CurrencyId = 1 THEN pp.Price ELSE CONVERT(DECIMAL(9, 2), (pp.Price * c.ExchangeRate)) END AS ExchangeRatePrice, price as OriginalPriceInDB, CASE WHEN pp.price IS NULL THEN 0 WHEN c.CurrencyId = 1 THEN pp.Price ELSE CONVERT(DECIMAL(9, 2), (pp.Price * c.ExchangeRate)) END * 10 AS CalculatedPrice, c.currencyid as Currency FROM PRODUCTPRICE pp, CURRENCY c

     ..but that means duplication & inherent risk of someone not updating both instances to keep in sync.

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     3/5

   • Can an interrupt handler be preempted?

     Top Answer

     Answered Aug 22, 2013 · 2 votes

     Simple answer: An interrupt can only be interrupted by interrupts of higher priority.

     Therefore an interrupt can be interrupted by the kernel or a user task if the interrupt's priority is lower than the kernel scheduler interrupt priority or user task interrupt priority.

     Note that by "user task" I mean user-defined interrupt.

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     4/5

   • Can a SQL Default Value be calculated?

     Top Answer

     Answered May 15, 2016 · 2 votes

     One method that works in all databases is to use a view:

     create view v_table as select t.*, concat(label, id) as label from foo t;-

     This would not allow you to change it. You could have a column in the table called something like override_label, which has a NULL default and then the view is:

     create view v_table as select t.*, coalesce(override_label, concat(label, id)) as label from foo t;-

     In some databases, you can do something similar with a computed column:

     alter table foo add label as (coalesce(override_label, concat(label, id)));-

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     5/5

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2. www.geeksforgeeks.org · what-is-interrupt-latencyWhat is Interrupt Latency? - GeeksforGeeks

   www.geeksforgeeks.org · what-is-interrupt-latency

   

   Feb 2, 2023 · Interrupt latency is the time that elapses between the occurrence of an interrupt and the execution of the first instruction of the interrupt service routine (ISR) that handles the interrupt. It is a measure of the system’s ability to respond to external events in a timely manner.

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4. stackoverflow.com · questions · 6891325real time - Estimating of interrupt latency on the x86 CPUs ...

   stackoverflow.com · questions · 6891325

   

   Jul 31, 2011 · You need to somehow take a timestamp at the time the interrupt reaches the processor and then another timestamp at the very beginning of the interrupt handler. An approximation of the interrupt latency can be calculated by subtracting the two.

5. www.embedded.com · introduction-to-interruptsEmbedded Systems: Interrupts & Latency

   www.embedded.com · introduction-to-interrupts

   

   Jun 1, 2001 · In simple cases, latency can be calculated from instruction times, but many modern systems with 32-bit CPUs, caches, and multiple interrupt sources, are far too complex for exact latency calculations.

6. community.arm.com · arm-community-blogs · bBeginner guide on interrupt latency and Arm Cortex-M ...

   community.arm.com · arm-community-blogs · b

   

   Apr 1, 2016 · The interrupt latency of Cortex-M processors can be affected by wait states of the on chip bus system, which can result in a small jitter. The Cortex-M0 and Cortex-M0+ processors have an optional feature to force interrupt response time to have zero jitter.

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7. www.nxp.com · docs · enMeasuring Interrupt Latency - NXP Semiconductors

   www.nxp.com · docs · en

   

   Introduction. The term interrupt latency refers to the delay between the start of an Interrupt Request (IRQ) and the start of the respective Interrupt Service Routine (ISR). The interrupt latency is expressed in core clock cycles.

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8. www.sciencedirect.com · interrupt-latencyInterrupt Latency - an overview | ScienceDirect Topics

   www.sciencedirect.com · interrupt-latency

   

   Interrupt latency is the interval of time from an external interrupt request signal being raised to the first fetch of an instruction of a specific interrupt service routine (ISR).

9. People also ask

   Can interrupt latency be calculated from instruction times?

   • In simple cases, latency can be calculated from instruction times, but many modern systems with 32-bit CPUs, caches, and multiple interrupt sources, are far too complex for exact latency calculations. Interrupt latency must be considered at design time, whenever responsiveness matters.

   Embedded Systems: Interrupts & Latency

   www.embedded.com/introduction-to-interrupts/

   See all results for this question

   How do you calculate interrupt latency?

   • You need to somehow take a timestamp at the time the interrupt reaches the processor and then another timestamp at the very beginning of the interrupt handler. An approximation of the interrupt latency can be calculated by subtracting the two.

   real time - Estimating of interrupt latency on the x86 CPUs - Stack

   stackoverflow.com/questions/6891325/estimating-of-interrupt-latency-on-the-x86-cpus

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   What is interrupt latency?

   • Interrupt latency is a measure of the time it takes for a computer system to respond to an external event, such as a hardware interrupt or software exception. This metric is important in determining the performance and responsiveness of a system and is a key consideration in the design and optimization of real-time and embedded systems.

   What is Interrupt Latency? - GeeksforGeeks

   www.geeksforgeeks.org/what-is-interrupt-latency/

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   What are the three types of latency?

   • There are three types of latency that are measured: The latency from the timer interrupts the ISR execution. The latency from the timer interrupts the RTOS highest priority task. The latency of the external GPIO interrupts response. Interrupt latency is a measure of the time it takes for a computer system to respond to an external event.

   What is Interrupt Latency? - GeeksforGeeks

   www.geeksforgeeks.org/what-is-interrupt-latency/

   See all results for this question

10. community.arm.com · arm-community-blogs · bBeginner guide on interrupt latency and Arm Cortex-M processors

    community.arm.com · arm-community-blogs · b

    

    Apr 1, 2016 · The interrupt latency of Cortex-M processors can be affected by wait states of the on chip bus system, which can result in a small jitter. The Cortex-M0 and Cortex-M0+ processors have an optional feature to force interrupt response time to have zero jitter.