All RTOS (linux Based ) Other than RT-Linux

mahi · External Since: Jul 10, 2007 Posts: 5

Hi all, I want to know, there are any REAL TIME OPERATING
systems( RTOS) which should have total linux compatible other than RT-
Linux.

And are there any free Real time Operating systems ( Linux Based ) is
available on the Internet.

Please provide some information regarding this issue.

The Natural Philosopher · External Since: Jul 09, 2004 Posts: 802

mahi wrote:
> Hi all, I want to know, there are any REAL TIME OPERATING
> systems( RTOS) which should have total linux compatible other than RT-
> Linux.
>
> And are there any free Real time Operating systems ( Linux Based ) is
> available on the Internet.
>
> Please provide some information regarding this issue.
>
What do you understand by:

Real time?
Linux compatible?

Matt Giwer · External Since: May 23, 2006 Posts: 295

mahi wrote:
> Hi all, I want to know, there are any REAL TIME OPERATING
> systems( RTOS) which should have total linux compatible other than RT-
> Linux.
>
> And are there any free Real time Operating systems ( Linux Based ) is
> available on the Internet.
>
> Please provide some information regarding this issue.

I have read that the kernel is interrupt driven rather than schedule driven. If
that is what you mean, all linuxes are real time.

--
The purpose of peace talks between Palestine and Israel is to prevent
Palestine from ever being free of the Israel occupation.
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The Natural Philosopher · External Since: Jul 09, 2004 Posts: 802

Matt Giwer wrote:
> mahi wrote:
>> Hi all, I want to know, there are any REAL TIME OPERATING
>> systems( RTOS) which should have total linux compatible other than RT-
>> Linux.
>>
>> And are there any free Real time Operating systems ( Linux Based ) is
>> available on the Internet.
>>
>> Please provide some information regarding this issue.
>
> I have read that the kernel is interrupt driven rather than schedule
> driven. If that is what you mean, all linuxes are real time.
>
Thats not generally enough for many peoples definitions, which is that
the time to respond to an (external) interrupt is fast, un blockable,
and well defined.

If you think of how many ways to stop your 'lunix' responding to a
keyboard interrupt exist, you will get my drift.

Most RTOSes are very lightweight and very carefully controlled in terms
of response time to interrupts.

Matt Giwer · External Since: May 23, 2006 Posts: 295

The Natural Philosopher wrote:
> Matt Giwer wrote:
>> mahi wrote:
>>> Hi all, I want to know, there are any REAL TIME OPERATING
>>> systems( RTOS) which should have total linux compatible other than RT-
>>> Linux.
>>> And are there any free Real time Operating systems ( Linux Based ) is
>>> available on the Internet.
>>> Please provide some information regarding this issue.
>> I have read that the kernel is interrupt driven rather than
>> schedule driven. If that is what you mean, all linuxes are real time.

> Thats not generally enough for many peoples definitions, which is that
> the time to respond to an (external) interrupt is fast, un blockable,
> and well defined.

I realize there are many definitions. However what you suggest is what "nice"
is for. Having a real time OS and tailoring it are two different matters.

> If you think of how many ways to stop your 'lunix' responding to a
> keyboard interrupt exist, you will get my drift.

Change the BIOS to no keyboard? Or something like that. The keyboard is not a
linux function. It only reads the BIOS.

> Most RTOSes are very lightweight and very carefully controlled in terms
> of response time to interrupts.

I have never become involved in tailoring a OS compile to single applications.
I have no idea how to do it. I have READ killing all the unneeded material is
possible.

--
Republicans are more interested in protecting the president than the troops.
-- The Iron Webmaster, 3839
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Hans-Peter Diettrich · External Since: Jul 22, 2007 Posts: 18

Matt Giwer wrote:

>> Hi all, I want to know, there are any REAL TIME OPERATING
>> systems( RTOS) which should have total linux compatible other than RT-
>> Linux.
>>
>> And are there any free Real time Operating systems ( Linux Based ) is
>> available on the Internet.
>>
>> Please provide some information regarding this issue.
>
>
> I have read that the kernel is interrupt driven rather than schedule
> driven. If that is what you mean, all linuxes are real time.

Real time systems typically guarantee some timing (interrupt
latency...), so that processes can react on events in a timely manner.
Furthermore the response on events has time constraints, i.e. a process
must lower its priority, after doing the time critical event handling.
This requires that *all* system processes behave accordingly, what's not
normally the case in an preemptive multitasking system. A related
requirement are memory-resident event handlers, separated somehow from
the less critical swappable parts of an process.

IMO these requirements cannot be satisfied with the public Linux code,
and also cannot be introduced by simple patches to the kernel etc. sources.

Some approaches make the Linux kernel simply an process, running under
control of an new RT kernel. But then RT processes will have to
communicate and cooperate with the RT kernel, so that they run more in
parallel to the Linux kernel, instead of controlled by the Linux kernel.
IMO it then is inevitable to split RT applications into an RT process,
running under control of the RT kernel, and an non-RT process, running
under control of the Linux kernel. One also might see the RT part as
kind of a device or driver, interacting with the remaining part of the
application.

IMO it will be simpler to use some available RT system, and make it's
ABI so Linux-compatible, that Linux applications can be installed into
such a system. But then it might be easier to install a veritable Linux
into a VM, hosted by the RT OS. See also: The Xen Project.

DoDi

The Natural Philosopher · External Since: Jul 09, 2004 Posts: 802

Matt Giwer wrote:
> The Natural Philosopher wrote:
>> Matt Giwer wrote:
>>> mahi wrote:
>>>> Hi all, I want to know, there are any REAL TIME OPERATING
>>>> systems( RTOS) which should have total linux compatible other than RT-
>>>> Linux.
>>>> And are there any free Real time Operating systems ( Linux Based ) is
>>>> available on the Internet.
>>>> Please provide some information regarding this issue.
>>> I have read that the kernel is interrupt driven rather than
>>> schedule driven. If that is what you mean, all linuxes are real time.
>
>> Thats not generally enough for many peoples definitions, which is that
>> the time to respond to an (external) interrupt is fast, un blockable,
>> and well defined.
>
> I realize there are many definitions. However what you suggest is
> what "nice" is for. Having a real time OS and tailoring it are two
> different matters.
>

With respect, it isn't.

>> If you think of how many ways to stop your 'lunix' responding to a
>> keyboard interrupt exist, you will get my drift.
>
> Change the BIOS to no keyboard? Or something like that. The keyboard
> is not a linux function. It only reads the BIOS.
>

Shows how little you know..most ROM BIOSES are TOTALLY bypassed by
linux. Their sole function is to get the OS in place with some form of
basic keyboard and screen control. In case intervention is needed.

After that the interrupt routines are installed by the kernel for pretty
much everything.

>> Most RTOSes are very lightweight and very carefully controlled in
>> terms of response time to interrupts.
>
> I have never become involved in tailoring a OS compile to single
> applications. I have no idea how to do it. I have READ killing all the
> unneeded material is possible.
>

Well it depends on what application you want to run..if its simple
enough you probably wouldn't bother with an OS at all. Or you would
write your own...it becomes less a question of what you remove that what
you decide to include..you wouldn't need multiuser capabilities
normally, though you might leave in a hierarchy of task priorities..you
might not even need a strict multitasking ability. If the program does
just one thing, that is processing some real time event and turning it
into an output, you can leave the processor in either a halt state, or
running in a null loop till an interrupt comes along.

Linux is a multiuser, multitasking general OS. Its not designed for real
time work. People use it and work round that by stripping it down and
having enough processor speed to cope with its deficiencies, and hoping
no bug or unforeseen events slow it or crash it..but is not the best way
to crack a real real-time application.

It's easier to buy in a proper RTOS with libc support and compile linux
stuff to that..if you want REAL millisecond response times.

The problem with Linux as its stands is that lots of stuff inside the
kernel may wait indeterminate times with most or all interrupts
disabled, waiting for a peripheral to respond. Sure mostly this is
engineered out for common cases: but there's plenty pf times that a
buggy bit of code can freeze out the rest of the machine by hogging
cycles or calling into the kernel to do something that doesn't complete
in a timely fashion. Where defined response times are a matter of life
and death - like in avionics, you will not find Linux.

Larry Blanchard · External Since: Oct 31, 2004 Posts: 32

Matt Giwer wrote:

>> Thats not generally enough for many peoples definitions, which is that
>> the time to respond to an (external) interrupt is fast, un blockable,
>> and well defined.
>
> I realize there are many definitions. However what you suggest is what
> "nice" is for. Having a real time OS and tailoring it are two different
> matters.

Actually, "nice" is for batch jobs vs interactive ones. Has nothing to do
with interrupts.

However, there are real-time extensions to Unix/Linux which allow fixed
priorities, no swapping, task activation/resumption on specified interrupts,
etc.. While not enough for "hard" real time with rapid responses, the
extensions are more than adequate for the average process control or SCADA
system. One of the projects I was involved in ran an aluminum smelter SCADA
system. It's been installed in several smelters around the world. Works
fine.

Use of the extensions does take a little getting used to. For example, to run
a task every 5 milliseconds one does not exit and request reactivation in the
said 5 milliseconds. Instead, request the time when activated and at the end
of each iteration request reactivation or resumption in 5 milliseconds minus
however long the current iteration took.

--
It's turtles, all the way down.

Matt Giwer · External Since: May 23, 2006 Posts: 295

The Natural Philosopher wrote:
> Matt Giwer wrote:
....
>> Change the BIOS to no keyboard? Or something like that. The
>> keyboard is not a linux function. It only reads the BIOS.

> Shows how little you know..most ROM BIOSES are TOTALLY bypassed by
> linux. Their sole function is to get the OS in place with some form of
> basic keyboard and screen control. In case intervention is needed.

I guess I have been confused by the necessity to have the BIOS reflect new
hardware before linux notices it is there.

--
As pf July 2007, the Iraq war is costing the same as three nuclear aircraft
carriers every month. Never again question the cost of a carrier.
-- The Iron Webmaster, 3841
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http://www.giwersworld.org/holo3/holo-survivors.phtml a13

Peter KÃ¶hlmann · External Since: Jun 27, 2005 Posts: 1500

Matt Giwer wrote:

> The Natural Philosopher wrote:
>> Matt Giwer wrote:
> ...
>>> Change the BIOS to no keyboard? Or something like that. The
>>> keyboard is not a linux function. It only reads the BIOS.
>
>> Shows how little you know..most ROM BIOSES are TOTALLY bypassed by
>> linux. Their sole function is to get the OS in place with some form of
>> basic keyboard and screen control. In case intervention is needed.
>
> I guess I have been confused by the necessity to have the BIOS reflect new
> hardware before linux notices it is there.
>

And right here you made the next error
--
Failure is not an option. It comes bundled with your Microsoft product.

Matt Giwer · External Since: May 23, 2006 Posts: 295

Peter Köhlmann wrote:
> Matt Giwer wrote:
>> The Natural Philosopher wrote:
>>> Matt Giwer wrote:
>> ...
>>>> Change the BIOS to no keyboard? Or something like that. The
>>>> keyboard is not a linux function. It only reads the BIOS.
>>> Shows how little you know..most ROM BIOSES are TOTALLY bypassed by
>>> linux. Their sole function is to get the OS in place with some form of
>>> basic keyboard and screen control. In case intervention is needed.
>> I guess I have been confused by the necessity to have the BIOS reflect new
>> hardware before linux notices it is there.

> And right here you made the next error

Odd that it is required. Perhaps you could take the time to explain.

--
Hodie postridie Nonas Augustas MMVII est
-- The Ferric Webceasar
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The Natural Philosopher · External Since: Jul 09, 2004 Posts: 802

Matt Giwer wrote:
> Peter Köhlmann wrote:
>> Matt Giwer wrote:
>>> The Natural Philosopher wrote:
>>>> Matt Giwer wrote:
>>> ...
>>>>> Change the BIOS to no keyboard? Or something like that. The
>>>>> keyboard is not a linux function. It only reads the BIOS.
>>>> Shows how little you know..most ROM BIOSES are TOTALLY bypassed by
>>>> linux. Their sole function is to get the OS in place with some form of
>>>> basic keyboard and screen control. In case intervention is needed.
>>> I guess I have been confused by the necessity to have the BIOS
>>> reflect new
>>> hardware before linux notices it is there.
>
>> And right here you made the next error
>
> Odd that it is required. Perhaps you could take the time to explain.
>

Th BIOS merely provide a set of routines that are hopefully

- enough to get the machine to boot something else and
- MAY be used by whatever else runs to access the hardware, but its only
MAY.

In fact most OS'es these days simply use the BIOS to bootstrap the boot
loader, and maybe access the boot disk: Once the OS is loaded it is
completely bypassed.

So in reality, all the BIOS dos in most systems is run the disk system
and select a boot drive, and provide a minimal amount of screen/keyboard
stuff for boot diagnostics.

John Hasler · External Since: Mar 25, 2004 Posts: 1337

The Natural Philosopher writes:
> In fact most OS'es these days simply use the BIOS to bootstrap the boot
> loader, and maybe access the boot disk

Linux itself does not use the BIOS at all. All bootloaders use it, but the
bootloader is not part of the OS.

> Once the OS is loaded it is completely bypassed.

Correct, but there may be hardware that is initialized by the BIOS.
--
John Hasler
john.RemoveThis@dhh.gt.org
Dancing Horse Hill
Elmwood, WI USA

Matt Giwer · External Since: May 23, 2006 Posts: 295

The Natural Philosopher wrote:
> Matt Giwer wrote:
>> Peter Köhlmann wrote:
>>> Matt Giwer wrote:
>>>> The Natural Philosopher wrote:
>>>>> Matt Giwer wrote:
>>>> ...
>>>>>> Change the BIOS to no keyboard? Or something like that. The
>>>>>> keyboard is not a linux function. It only reads the BIOS.
>>>>> Shows how little you know..most ROM BIOSES are TOTALLY bypassed by
>>>>> linux. Their sole function is to get the OS in place with some form of
>>>>> basic keyboard and screen control. In case intervention is needed.
>>>> I guess I have been confused by the necessity to have the BIOS
>>>> reflect new
>>>> hardware before linux notices it is there.
>>> And right here you made the next error
>> Odd that it is required. Perhaps you could take the time to explain.

> Th BIOS merely provide a set of routines that are hopefully

> - enough to get the machine to boot something else and
> - MAY be used by whatever else runs to access the hardware, but its only
> MAY.

> In fact most OS'es these days simply use the BIOS to bootstrap the boot
> loader, and maybe access the boot disk: Once the OS is loaded it is
> completely bypassed.

> So in reality, all the BIOS dos in most systems is run the disk system
> and select a boot drive, and provide a minimal amount of screen/keyboard
> stuff for boot diagnostics.

What started this was my statement that the keypresses are found by accessing
BIOS.

However my experience is that all hardware changes have to be registered in
BIOS before they are recognized by the OS, linux or otherwise. I can see how
once in BIOS the OS knows what to "look" for and then deal with it.

Not having actually followed the motherboard traces from the keyboard plug to
see where they lead I cannot swear the BIOS is the only place where an OS can
get the keypresses. However if the BIOS is not needed what his the physical
access point the linux uses to get the keypress data?

--
Al Qaeda is back to its pre-911 strength of 300. I am so frightened I can
only laugh to relieve the anxiety. 300 is the highest US government estimate
of their numbers ever made public.
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Hans-Peter Diettrich · External Since: Jul 22, 2007 Posts: 18

Matt Giwer wrote:

> Not having actually followed the motherboard traces from the
> keyboard plug to see where they lead I cannot swear the BIOS is the only
> place where an OS can get the keypresses. However if the BIOS is not
> needed what his the physical access point the linux uses to get the
> keypress data?

It depends on the physical device. A PS/2 keyboard is connected to
different hardware, and is served by a different handler, than is e.g. a
wireless USB keyboard. When the OS installs drivers, for all physical
devices, the drivers return the logical device type, e.g. display, HD.
On universal adapters, like SCSI or USB, every connected device can be
of an different type. The OS will send (or receive) requests to logical
devices, which are translated by the handler into commands to the
physical device.

DoDi

The Natural Philosopher · External Since: Jul 09, 2004 Posts: 802

Matt Giwer wrote:
> The Natural Philosopher wrote:
>> Matt Giwer wrote:
>>> Peter Köhlmann wrote:
>>>> Matt Giwer wrote:
>>>>> The Natural Philosopher wrote:
>>>>>> Matt Giwer wrote:
>>>>> ...
>>>>>>> Change the BIOS to no keyboard? Or something like that. The
>>>>>>> keyboard is not a linux function. It only reads the BIOS.
>>>>>> Shows how little you know..most ROM BIOSES are TOTALLY bypassed by
>>>>>> linux. Their sole function is to get the OS in place with some
>>>>>> form of
>>>>>> basic keyboard and screen control. In case intervention is needed.
>>>>> I guess I have been confused by the necessity to have the BIOS
>>>>> reflect new
>>>>> hardware before linux notices it is there.
>>>> And right here you made the next error
>>> Odd that it is required. Perhaps you could take the time to explain.
>
>> Th BIOS merely provide a set of routines that are hopefully
>
>> - enough to get the machine to boot something else and
>> - MAY be used by whatever else runs to access the hardware, but its
>> only MAY.
>
>> In fact most OS'es these days simply use the BIOS to bootstrap the
>> boot loader, and maybe access the boot disk: Once the OS is loaded it
>> is completely bypassed.
>
>> So in reality, all the BIOS dos in most systems is run the disk system
>> and select a boot drive, and provide a minimal amount of
>> screen/keyboard stuff for boot diagnostics.
>
> What started this was my statement that the keypresses are found by
> accessing BIOS.
>
> However my experience is that all hardware changes have to be
> registered in BIOS before they are recognized by the OS, linux or
> otherwise. I can see how once in BIOS the OS knows what to "look" for
> and then deal with it.
>
> Not having actually followed the motherboard traces from the
> keyboard plug to see where they lead I cannot swear the BIOS is the only
> place where an OS can get the keypresses. However if the BIOS is not
> needed what his the physical access point the linux uses to get the
> keypress data?
>

Interrupt off the hardware controller that services the keyboard.

The vectors for these are held in RAM. They can be changed. You can
install your own. Most systems do. IIRC the first thing a bios will do
on boot is set these vectors up. Until it does the keyboard won;t work.
As soon as the OS kernel comes in, it will rewrite some or all of them
to point to its handlers.

What happens is that - say - a keypress is recogniosed by the keyboard
peripheral chip. A small computer in its own right, whose job is to wait
for keypresses and maybe mouse movements and the like. These days its
probably the generic USB controller, and every time a block of data
comes in,depending on how its programmed, it will either raise an
interrupt line on every byte, or when its small internal buffer is full.

The interrupt lines go into another small piece of hardware - the
interrupt controller - and that will register which peripheral has
raised the interrupt, and pass a general interrupt along to the
processsor, which will stop, shove its program counter in the stack,
read the interrupt NUMBER from teh interrupt controller, and jump
immdiately to the contents of teh NUMBERE'th row of a table held in
(low?) RAM That might at one time have been pointing at BIOS ROM, but
fter te OS has does its laoding, itr won;t be. It will point to the USB
interrupt service routine.

What THAT des is read te USB device directly, and find out something
about the device that caused the USB port to wake up. Decide its a
keyboard key press and jump to a specific bit of code that will reda
that byte of data, put it in a buffer, raise a flag to say 'keyboard
data available' and then probabably call the scheduling part of the
multitasker to tell it to resume any threads that are halted pending
keyboard input. Then it will issue a return from interrupt and teh
processor will resume what it was doing by popping its program cunter
from the stack.

Now the next time the scheduler suspends the thread the processor was
executing, it will immediately resume whatever task(s) was/were waiting
for keyboard input. In whatever priority they were listed. Example: Some
keys are flagged as super keys' and may be examined and acted on by the
low level daemons..a break key for example will be examined by low level
software t see if it means it needs to do Something Awful. So every
process that MIGHT want to know what key is pressed or what button is
clicked must examine all the inputs, and if they decide its not for
them, leave it there and go back to sleep. Finally someone - say the
application focus - gets the keystroke and says 'aha' I must type an A
on the application..AND REMOVE IT FROM THE BUFFER. At this point its
gone, No other application will get it, and if there are other lower
priority task that might be waiting for it, they will either find no
data, or won't even be woken up. If the keyboard interface is written
well, it will call the scheduler when the command 'empty the buffer' is
received and clear all wakeup flags from threads waiting for keyboard input.

Don;'t hold me to the exact details of this, buts thats broadly how it
happened the last time I wrote this sort of stuff, which was 20 years
ago on an 8086... Smile

The fundamental thing is that a BIOS ONLY has to carry enough code to
boot the OS. Essentially that means

- set up a basic screen and keyboard and disk driver kernel
- read the NVRAM to find out where to boot from, and what type of built
in driver to use.
-load and dive into the boot loader
- bye bye kansas.

After that the whole machine apart from the BIOS PROMS is available
for modification, and in most cases, it will be modified completely.

In general the kernel will rush around interrogating I/O ports to find
responses it recognises, and setting up handlers for what it finds: In
case of unknown issues, it will refer to its disk based config files to
load the correct stuff. Once it is relatively happy, it will launch the
init daemon, which looks in ITS config files and carries on spawning
daemons that get the machine up and running, until it finally spawns
some kind of user interface.

At that point the BIOS is just a set of ROMS, idle and silent, and
completely forgotten.

If for no other reason than the ROM bus speed is often WAY below the RAM
bus speed: Using the ROMS will slow you down.

So, The onboard ROM BIOS only needs to understand the boot hardware. Of
course you COULD talk about the hardware interface systems in the kernel
as a BIOS as well, and be correct to do so, but BIOS on Intel machines
of the PC variety is generally held to be that part that comes with the
hardware in ROM: In a Linux context the terns 'device drivers' or
'device subsystem' and 'kernel' would be used instead to talk about
various aspects of the kernel that deal with interfacing with the hardware.

I hope that helps.

Matt Giwer · External Since: May 23, 2006 Posts: 295

The Natural Philosopher wrote:
....
> I hope that helps.

Yes, thank you.

--
Every paid position as a university professor originated as a labor of love
without any form of financial reward.
-- The Iron Webmaster, 3849
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