Interrupt latency in RTEMS (Zedboard)

[Rehab Massoud]

Well, I didn't mention that because I can't guess why. However, I had what
could be a similar thing before, but with Leon3 implemented on the logic of
the Zedboard. When I traced down the BSP code (which wasn't RTEMS, I used
the bcc there as far as I remember) it really didn't contain anything that
would make the measurements differ if you changed the number of ticks per
microsecond. So if it's a similar reason, you could figure it out by
tracing the code from the top RTEMS api's down to the Board support
package.
On Mar 27, 2018 14:02, "BRIARD Sebastien" <
sebastien.briard at thalesaleniaspace.com> wrote:

> Good point. Thanks.
>
> Would you have any idea concerning my other question ? (why I get the same
> result for interrupt latency with different values of Tick per microsecond )
>
>
>
> *De :* Rehab Massoud [mailto:rehab.massoud at gmail.com]
> *Envoyé :* mardi 27 mars 2018 13:57
> *À :* BRIARD Sebastien
> *Cc :* rtems-users at rtems.org
> *Objet :* RE: Interrupt latency in RTEMS (Zedboard)
>
>
>
> Needless to say also you can't measure software execution time that
> accurately with software. It's not only that it's intrusive but also would
> never be cycle accurate. If you really need such cycle accuracy you might
> think about hardware-based tracing techniques.
>
> On Mar 27, 2018 13:52, "BRIARD Sebastien" <sebastien.briard@
> thalesaleniaspace.com> wrote:
>
> Yeah, hardware limits to 1.5ns if we take in account the max frequency of
> the cortex. (That was the more or less 1ns =) )
>
>
>
> *De :* Rehab Massoud [mailto:rehab.massoud at gmail.com]
> *Envoyé :* mardi 27 mars 2018 13:49
> *À :* BRIARD Sebastien; rtems-users at rtems.org
> *Objet :* Re: Interrupt latency in RTEMS (Zedboard)
>
>
>
> Hi, the smaller theoretical delay accuracy you can measure (without adding
> to an ASIC cascaded FF) is one clock cycle. I think the maximum frequency
> that could be achieved on zedboard is not more than 800 MHz, and the
> maximum Zync's Cortex freq per Zedboard's datasheet is 667 MHz, which means
> you can't achieve 1 nanosecond accuracy even with hardware measurements,
> right?
>
> On Mar 27, 2018 13:30, "BRIARD Sebastien" <sebastien.briard@
> thalesaleniaspace.com> wrote:
>
>
>
>
>
> *De :* BRIARD Sebastien
> *Envoyé :* mardi 27 mars 2018 11:42
> *À :* 'users at rtems.org'
> *Objet :* Interrupt latency in RTEMS (Zedboard)
>
>
>
> Hi,
>
>
>
> I was trying to measure the interrupt latency in RTEMS with a Xilinx Zynq
> Zedboard (cortex A9).
> I modified the c file in classic_signal example to measure time in the
> main loop and right after entering the handler.
> That might seem artificial but well, it gives me a value with a relatively
> simple code.
>
> I used this code for 100, 10000, and one million ticks per second. I am
> trying to understand how the measure can quite equal with 100 ticks per
> second and a million.
> (I obtained values between 500ns and 1000ns).
> Is there another timer that is used for interrupt processing ?
>
> A subsequent question, is it possible to use a larger value than a tick
> per microsecond ?  Maybe I am confusing a little between frequency and tick
> clock in RTEMS but I would like to run test with more or less a tick per
> nanosecond.
>
> Thank you,
> Sébastien.
>
>
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