Reply by 42Bastian Schick●September 14, 20072007-09-14
On Mon, 10 Sep 2007 15:39:54 GMT, "FreeRTOS.org" <noemail@address.com>
wrote:
>I receive questionnaires occasionally from researchers, magazines, etc with
>reference to FreeRTOS.org. My favourite question is "What is the context
>switch time?".
Mine too.
>you want me to measure?" The answer came back "The time to switch from one
>task to another". I could not resist "On a PIC18 or a Pentium?" - to which
>they replied "whatever the average is". Enough said.
I once gave the numbers for a "imaginary" 1GHz ARM7 which impressed
them :-))
--
42Bastian
Do not email to bastian42@yahoo.com, it's a spam-only account :-)
Use <same-name>@monlynx.de instead !
Reply by David Brown●September 11, 20072007-09-11
Jim Granville wrote:
> Stargazer wrote:
>
>> Greetings,
>>
>> I am wondering are there RTOSes that document interrupt and task
>> switching latencies on supported platforms and provide with tools to
>> validate that. I read some advertising hype from OS vendors on how
>> small their latencies are, but there were no numbers. There were also
>> several independent studies that got to numbers, which OS salesmen
>> probably prayed would have never been published :-)
>>
>> So does anybody knows RTOS(es) that do document and validate the
>> latencies on supported platforms?
>
> I came across this recently
> http://www.innovasic.com/
>
> Their Fido1100 seems to have a real-time focus, and they
> quote system jitter times, and MAX's, so you might get
> into there.
>
Have you any ideas how good these devices are? They certainly sound
interesting.
Reply by Didi●September 10, 20072007-09-10
> I receive questionnaires occasionally from researchers, magazines, etc wi=
th
> reference to FreeRTOS.org. My favourite question is "What is the context
> switch time?". Last time I got this I wrote back and said, "what exactly=
to
> you want me to measure?" The answer came back "The time to switch from o=
ne
> task to another". I could not resist "On a PIC18 or a Pentium?" - to whi=
ch
> they replied "whatever the average is". Enough said.
"Average" is good, LOL. While the time a task switch takes on a given
system might be of interest, this is only minor anyway.
What really matters is the IRQ latency (the OP _did_ ask about it
which is pretty untypical, looks like he knows what he is after).
This is again platform dependent, of course, but if I were to
buy a system (which I am not, I am rather selling one) I would
like to know whether the scheduler unmasks the IRQ while switching
tasks, are there system calls which keep the IRQ masked for longer
than others etc.
On top of that there is code like device drivers etc. low level
stuff which can also mask the interrupts, and while these may or may
not be part of an OS just one of the wrong "model" could kill the
latency figure beyond usability...
Dimiter
------------------------------------------------------
Dimiter Popoff Transgalactic Instruments
http://www.tgi-sci.com
------------------------------------------------------
On Sep 10, 6:39 pm, "FreeRTOS.org" <noem...@address.com> wrote:
> "Stargazer" <stargazer3...@gmail.com> wrote in message
>
> news:1189427264.040957.138540@g4g2000hsf.googlegroups.com...
>
> > Greetings,
>
> > I am wondering are there RTOSes that document interrupt and task
> > switching latencies on supported platforms and provide with tools to
> > validate that. I read some advertising hype from OS vendors on how
> > small their latencies are, but there were no numbers. There were also
> > several independent studies that got to numbers, which OS salesmen
> > probably prayed would have never been published :-)
>
> > So does anybody knows RTOS(es) that do document and validate the
> > latencies on supported platforms?
>
> Don't believe anything you read - measure it yourself. Be very careful as
> to exactly WHAT any measurements are actually measuring, and that the OS
> state is consistent across all your tests.
>
> I receive questionnaires occasionally from researchers, magazines, etc wi=
th
> reference to FreeRTOS.org. My favourite question is "What is the context
> switch time?". Last time I got this I wrote back and said, "what exactly=
to
> you want me to measure?" The answer came back "The time to switch from o=
ne
> task to another". I could not resist "On a PIC18 or a Pentium?" - to whi=
ch
> they replied "whatever the average is". Enough said.
>
> Another of my favourite quotes from an advert "20% faster context switch
> time", with no reference to what. LOL. Another, "fastest boot time, onl=
y x
> micro seconds" - without saying what is performed during the boot. Its a=
ll
> bull.
>
> BTW, FreeRTOS.org does publish some numbers, but these are rather out of
> date. SafeRTOS has timing figures for nearly all operations (it has to f=
or
> safety critical use), but this is only available in the purchased
> documentation or under NDA.
>
> --
> Regards,
> Richard.
>
> +http://www.FreeRTOS.org
> 13 official architecture ports, 1000 downloads per week.
>
> +http://www.SafeRTOS.com
> Certified by T=DCV as meeting the requirements for safety related systems.
Reply by Jim Granville●September 10, 20072007-09-10
Stargazer wrote:
> Greetings,
>
> I am wondering are there RTOSes that document interrupt and task
> switching latencies on supported platforms and provide with tools to
> validate that. I read some advertising hype from OS vendors on how
> small their latencies are, but there were no numbers. There were also
> several independent studies that got to numbers, which OS salesmen
> probably prayed would have never been published :-)
>
> So does anybody knows RTOS(es) that do document and validate the
> latencies on supported platforms?
I came across this recently
http://www.innovasic.com/
Their Fido1100 seems to have a real-time focus, and they
quote system jitter times, and MAX's, so you might get
into there.
-jg
Reply by husterk●September 10, 20072007-09-10
On Sep 10, 8:27 am, Stargazer <stargazer3...@gmail.com> wrote:
> Greetings,
>
> I am wondering are there RTOSes that document interrupt and task
> switching latencies on supported platforms and provide with tools to
> validate that. I read some advertising hype from OS vendors on how
> small their latencies are, but there were no numbers. There were also
> several independent studies that got to numbers, which OS salesmen
> probably prayed would have never been published :-)
>
> So does anybody knows RTOS(es) that do document and validate the
> latencies on supported platforms?
>
> D
ThreadX, from Express Logic, also provides this information. They
offer hard numbers on specific processors that they have tested with.
There are also a number of compilers that support "OS Awareness" for
ThreadX which allow you to perform your own timing analysis on your
specific processor. Just remember that these numbers are only valid if
you follow the rules for your specific processor and / or operating
system.
Reply by FreeRTOS.org●September 10, 20072007-09-10
"Stargazer" <stargazer3p14@gmail.com> wrote in message
news:1189427264.040957.138540@g4g2000hsf.googlegroups.com...
> Greetings,
>
> I am wondering are there RTOSes that document interrupt and task
> switching latencies on supported platforms and provide with tools to
> validate that. I read some advertising hype from OS vendors on how
> small their latencies are, but there were no numbers. There were also
> several independent studies that got to numbers, which OS salesmen
> probably prayed would have never been published :-)
>
> So does anybody knows RTOS(es) that do document and validate the
> latencies on supported platforms?
>
Don't believe anything you read - measure it yourself. Be very careful as
to exactly WHAT any measurements are actually measuring, and that the OS
state is consistent across all your tests.
I receive questionnaires occasionally from researchers, magazines, etc with
reference to FreeRTOS.org. My favourite question is "What is the context
switch time?". Last time I got this I wrote back and said, "what exactly to
you want me to measure?" The answer came back "The time to switch from one
task to another". I could not resist "On a PIC18 or a Pentium?" - to which
they replied "whatever the average is". Enough said.
Another of my favourite quotes from an advert "20% faster context switch
time", with no reference to what. LOL. Another, "fastest boot time, only x
micro seconds" - without saying what is performed during the boot. Its all
bull.
BTW, FreeRTOS.org does publish some numbers, but these are rather out of
date. SafeRTOS has timing figures for nearly all operations (it has to for
safety critical use), but this is only available in the purchased
documentation or under NDA.
--
Regards,
Richard.
+ http://www.FreeRTOS.org
13 official architecture ports, 1000 downloads per week.
+ http://www.SafeRTOS.com
Certified by T�V as meeting the requirements for safety related systems.
Reply by Vladimir Vassilevsky●September 10, 20072007-09-10
Stargazer wrote:
> I am wondering are there RTOSes that document interrupt and task
> switching latencies on supported platforms and provide with tools to
> validate that. I read some advertising hype from OS vendors on how
> small their latencies are, but there were no numbers. There were also
> several independent studies that got to numbers, which OS salesmen
> probably prayed would have never been published :-)
Those numbers are VERY dependent on the particular hardware/software,
the mode of operation, the number of tasks and critical sections, wait
states, DMAs, buses/caches/SDRAMs, etc. It is simple enough to figure
out the latencies for the best case, however it is difficult if not
impossible to account for the worst case.
> So does anybody knows RTOS(es) that do document and validate the
> latencies on supported platforms?
You have to check it for yourself anyway, by toggling LEDs and tracing
with a scope.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Reply by Tim Wescott●September 10, 20072007-09-10
On Mon, 10 Sep 2007 05:27:44 -0700, Stargazer wrote:
> Greetings,
>
> I am wondering are there RTOSes that document interrupt and task
> switching latencies on supported platforms and provide with tools to
> validate that. I read some advertising hype from OS vendors on how
> small their latencies are, but there were no numbers. There were also
> several independent studies that got to numbers, which OS salesmen
> probably prayed would have never been published :-)
>
> So does anybody knows RTOS(es) that do document and validate the
> latencies on supported platforms?
>
I tend to be deeply suspicious of any self-reported OS timing measures,
particularly latencies. Generally if I really need to know I instrument
the code to toggle a pin when the task starts, then I look at the
interrupt source (if it's external) on an oscilloscope and compare it to
the task start. If I'm being really thorough I'll instrument the ISR,
also. This gives me a trace that goes:
_______________________________________
___|
____|____________|_________________________
Note that if you have something that's _really_ time critical, and if
you're blessed by it being simple, then you want to do it in the ISR, or
even design it into hardware. Also, should latency be important, you need
to be strict about protecting chunks of code -- the execution time of any
block of code that's protected from interrupts adds directly to the
interrupt latency.
--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com
Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Reply by Grant Edwards●September 10, 20072007-09-10
On 2007-09-10, borkhuis@gmail.com <borkhuis@gmail.com> wrote:
> On Sep 10, 2:27 pm, Stargazer <stargazer3...@gmail.com> wrote:
>> Greetings,
>>
>> I am wondering are there RTOSes that document interrupt and task
>> switching latencies on supported platforms and provide with tools to
>> validate that. I read some advertising hype from OS vendors on how
>> small their latencies are, but there were no numbers. There were also
>> several independent studies that got to numbers, which OS salesmen
>> probably prayed would have never been published :-)
>>
>> So does anybody knows RTOS(es) that do document and validate the
>> latencies on supported platforms?
>
> I know that VxWorks has a testsuite that does measure a lot of things
> including task switches, etc.
As does eCos.
--
Grant Edwards grante Yow! If I felt any more
at SOPHISTICATED I would DIE
visi.com of EMBARRASSMENT!
Reply by Pete Fenelon●September 10, 20072007-09-10
Stargazer <stargazer3p14@gmail.com> wrote:
> Greetings,
>
> I am wondering are there RTOSes that document interrupt and task
> switching latencies on supported platforms and provide with tools to
> validate that. I read some advertising hype from OS vendors on how
> small their latencies are, but there were no numbers. There were also
> several independent studies that got to numbers, which OS salesmen
> probably prayed would have never been published :-)
>
> So does anybody knows RTOS(es) that do document and validate the
> latencies on supported platforms?
RTA-OSEK from ETAS does. The "Binding Manual" provides full details of
all latencies and WCETs in the OS - these are validated on a reference
board, and the intention was that the Timing Characterisation Library
that enabled these latencies to be measured should be available to
customers to determine these figures on their own hardware.
Disclaimer - I used to work there...
pete
--
pete@fenelon.com "how many clever men have called the sun a fool?"