Il 29/11/2012 13:07, Chris ha scritto:
>
>
> >> A hard real time OS is an OS that guarantees to meet a deadline
> deterministically.
> >> A soft real time OS (usually called RTOS) usually or generally meet
> a deadline.
>
> I would echo the comments of all the other experienced programmers here.
>
I suppose to be experienced at least as much engineers answered until
now.
And I think to be a little bit more expert then engineers not knowing
the difference between a soft RTOS and a hard RTOS.
And much more expert then engineers not knowing that hard RTOS exists,
are used and that their use is mandatory in some application areas in
fields of military, space and transport systems.
So, don't tell me what I don't need to hear, I normally design
applications using or not soft RTOS, some times I need hard RTOS and I
use them.
This time the problem is to know if is there anyone that used before a
hard RTOS with LPC ARM and Cortex microcontrollers because those I
quickly tested until now are not so good (too complex then necessary or
without required tools and so on) or too much expensive for my customer.
Hard RTOS aren't only "theoretically" possible, they exists and are
normally used and they work pretty well. Writing sw using a hard RTOS is
also different then writing sw for s soft RTOS because you have to know
and define constraints and calculate (using some tools) if the
application is schedulable within its constraints.
So, many thanks to everyone but there is no space to change the
requirement about using a hard RTOS because not only is mandatory but
have to be certified that is really a hard RTOS.
> These kinds of definitions are "idealistic" and you
are trying to
> "over simplify"
> and paint a complex subject as a "Black&White" picture,
> when in reality it is all "Shades of Gray". Far more complex than you
> describe.
>
> I have used FreeRTOS for many projects now with LPC MCUs.
> It's a high quality RTOS, it does what an RTOS should do.
>
> I can write good code for it, and get everything done
> "deterministically" the way I want.
> I can also write crappy bad code that does not handle timing and has
> problems.
>
> So what do either of those results have to do with the RTOS? Nothing.
> It is your code.
>
> Any RTOS is nothing more than a tool kit: Threads, Mutexes, INTs, etc.
> What you do with those tools and how you use them is up to you.
> The RTOS cannot make those choices for you. Every project has
> different needs.
>
> When you talk about high reliability systems, well you can have
> multiple MCUs running
> in parallel with independent RTOS's, and have a voting election
> between them for all decisions.
> Nice idea, but even those systems fail. Just ask NASA.
>
> Chris.
>
>
Hard real time RTOS
Started by ●November 28, 2012
Reply by ●November 29, 20122012-11-29
Reply by ●November 29, 20122012-11-29
> > is there anyone using or that used in the past a
hard real time OS with
> > LPC series of microcontrollers?
> > Regards,
>
> If I were to answer your question as literally as you have stated it I
>
would just say "yes", and leave it at that.
>
>
I assume however you are asking for an as yet unstated reason, so to try
> and guess your next questions [I spend a lot of time on technical
> support guessing things] I suggest looking at the following link for
> several FreeRTOS on LPC projects:
>
> http://www.lpcware.com/
There are many other RTOSs available for the LPC family that do not appear in that list. For example, ChibiOS supports many LPC parts but does not appear in the list: http://www.chibios.org/dokuwiki/doku.php?id=chibios:architectures. My RTOS, NuttX, also supports several members of the LPC family: http://www.nuttx.org and is not in the list.
Greg
> > LPC series of microcontrollers?
> > Regards,
>
> If I were to answer your question as literally as you have stated it I
>
would just say "yes", and leave it at that.
>
>
I assume however you are asking for an as yet unstated reason, so to try
> and guess your next questions [I spend a lot of time on technical
> support guessing things] I suggest looking at the following link for
> several FreeRTOS on LPC projects:
>
> http://www.lpcware.com/
There are many other RTOSs available for the LPC family that do not appear in that list. For example, ChibiOS supports many LPC parts but does not appear in the list: http://www.chibios.org/dokuwiki/doku.php?id=chibios:architectures. My RTOS, NuttX, also supports several members of the LPC family: http://www.nuttx.org and is not in the list.
Greg
Reply by ●November 29, 20122012-11-29
--- In l..., "M. Manca" wrote:
> I personally used hard RTOS in the past but there is no port for
Please share the specifics about this system.
Which RTOS, what processor, what speed, amount of memory, etc, etc.
The classes I took sooo many years ago, stated that "Hard Real Time" was not possible.
It's a marketing term.
"Best Real Time" with what you have, is more like it.
Hard Real Time maybe just fine with a PIC16 in one application.
But a 3GHZ XXYYZZ processor will not cut it in another application.
Its the design of the system that gives you " Hard Real Time" response.
Not a single piece of software (RTOS) or single piece of silicon (CPU) can give you that.
don
> I personally used hard RTOS in the past but there is no port for
Please share the specifics about this system.
Which RTOS, what processor, what speed, amount of memory, etc, etc.
The classes I took sooo many years ago, stated that "Hard Real Time" was not possible.
It's a marketing term.
"Best Real Time" with what you have, is more like it.
Hard Real Time maybe just fine with a PIC16 in one application.
But a 3GHZ XXYYZZ processor will not cut it in another application.
Its the design of the system that gives you " Hard Real Time" response.
Not a single piece of software (RTOS) or single piece of silicon (CPU) can give you that.
don
Reply by ●November 29, 20122012-11-29
--- In l..., "M. Manca" wrote:
>
> So, now I thin it is clear what I am searching for.
So what you are implying is that software can meet the REAL TIME" requirement.
This is far from clear.
don
>
> So, now I thin it is clear what I am searching for.
So what you are implying is that software can meet the REAL TIME" requirement.
This is far from clear.
don
Reply by ●November 30, 20122012-11-30
--- In l..., dave@... wrote:
>
> Besides meeting a deadline, there are certain things that need to be done
> synchronously. For example, taking measurements at equally spaced
> intervals, or clocking steps to a stepper motor. Jitter in either of
> those processes has ill effects.
>
> I don't know what task managers are available commercially because I've
> always used my one, first written in 1978.
>
> DaveS
>
> > Hi
> >
> >> In my understanding FreeRTOS doesn't meet, it should be a soft RTOS
> >> because it doesn't assure to deterministically meet deadlines.
> >> My question is just if there is someone using a hard RTOS with LPC2xxx
> >> or LPC1xxx families of microcontrollers, what is and why choosed that
> >> RTOS.
> >
> > What you want is an RTOS with an deadline scheduler, that is one, that
> > modifies the priorities of tasks according their deadline (earliest
> > deadline first).
> >
> > Most RTOSs around use a pre-emptive priority based scheduler which can be
> > used to mimic a DL-scheduler by the application.
> >
> > Actually, I don't know of any DL-scheduler RTOS. I know OSE had one on top
> > of its normal scheduling some years ago.
> >
> > --
> > 42Bastian
> > +
> > | http://www.sciopta.com
> > | Fastest direct message passing kernel.
> > | IEC61508 certified.
> > +
> At some point, if you're going to do a lot of time sensitive stuff, it's good to look at the hardware assets that are available.
We have discovered the immense power of the DMA and timer subsystems on these chips, and the advantages of being able to time stuff to a single processor clock.
Once you get the small number of time critical challenges taken care of, you can just get a RTOS running, and forget about all that hard stuff.
>
> Besides meeting a deadline, there are certain things that need to be done
> synchronously. For example, taking measurements at equally spaced
> intervals, or clocking steps to a stepper motor. Jitter in either of
> those processes has ill effects.
>
> I don't know what task managers are available commercially because I've
> always used my one, first written in 1978.
>
> DaveS
>
> > Hi
> >
> >> In my understanding FreeRTOS doesn't meet, it should be a soft RTOS
> >> because it doesn't assure to deterministically meet deadlines.
> >> My question is just if there is someone using a hard RTOS with LPC2xxx
> >> or LPC1xxx families of microcontrollers, what is and why choosed that
> >> RTOS.
> >
> > What you want is an RTOS with an deadline scheduler, that is one, that
> > modifies the priorities of tasks according their deadline (earliest
> > deadline first).
> >
> > Most RTOSs around use a pre-emptive priority based scheduler which can be
> > used to mimic a DL-scheduler by the application.
> >
> > Actually, I don't know of any DL-scheduler RTOS. I know OSE had one on top
> > of its normal scheduling some years ago.
> >
> > --
> > 42Bastian
> > +
> > | http://www.sciopta.com
> > | Fastest direct message passing kernel.
> > | IEC61508 certified.
> > +
> At some point, if you're going to do a lot of time sensitive stuff, it's good to look at the hardware assets that are available.
We have discovered the immense power of the DMA and timer subsystems on these chips, and the advantages of being able to time stuff to a single processor clock.
Once you get the small number of time critical challenges taken care of, you can just get a RTOS running, and forget about all that hard stuff.