I want to synchronize a user space thread to an external event that
generates an interrupt. I thought of using the following approach: the
ISR that treats the interrupt does a quick processing (such as data
capture and buffering) and then sends data to the user space thread
through a message queue or signals to the thread waiting on a
semaphore and it gets the buffered data from shared memory or some
similar mechanism. So far I haven't succeded in finding a way to do
it. I've tryed to write a module which uses semaphores (<linux/sem.h>)
but aparently there is no way to use SysV IPC primitives in kernel
modules.

I would appreciate having hints on how to do it or pointers to
documentation and example code if available.

Thank you very much in advance for your help.

Elder.

Mad@Spammers wrote:
A user-space signal is the equivalent of an interrupt.
When user-space drivers are involved, I like to use
"send_sig_info()" to send a signal to the user-space
task to indicate changes in the state of the driver.

I like to model the user/kernel space interface to
look like a hardware device in terms of interrupt/signal
handling, with ioctl's to acknowledge/enable/disable
signals/interrupts from the driver. However, I'm an
embedded type that is used to that kind of thing ;-)

Getting the data to/from kernel space is another
issue, typically done by the read/write driver
interface, or by using mmap().

--
Michael N. Moran (h) 770 516 7918
5009 Old Field Ct. (c) 678 521 5460
Kennesaw, GA, USA 30144 http://mnmoran.org

"... abstractions save us time working, but they don't
save us time learning."
Joel Spolsky, The Law of Leaky Abstractions

The Beatles were wrong: 1 & 1 & 1 is 1

On 29 Apr 2004, Mad@Spammers wrote:

Maybe the ongoing work about D-Bus can give you inspiration:
<http://freedesktop.org/Software/dbus>
One of its motivations was/is exactly to be able to do more driver stuff in
user space, and I got the impression that that was what you are looking
for...

Herman
--
K.U.Leuven, Mechanical Eng., Mechatronics & Robotics Research Group
<http://people.mech.kuleuven.ac.be/~bruyninc> Tel: +32 16 322480

Michael N. Moran wrote:
What kind of time resolution do you need?

One other option is to use netlink sockets. They're
pretty easy. One drawback is netlink socket addresses
are somewhat precious, a little like signal numbers.

- Dan

You could use wait queues. Have your user process sleep on a queue and have
your ISR wake processes on that queue.

Hello Elder,

- Let your driver register a character interface
- from your user space thread, do a synchronous read.
- in your interrupt routine, copy the data and wakeup the
waiting thread.

Very common situation. Works without any problem for me.

best regards

Wolfgang Mües

Wolfgang Mües wrote:

Look twice at this approach! This is the UNIX way - everything is a file.

Read about the (now) old OSS audio drivers for block devices - same
data size on every read or write.
Or serial ports for character devices.

/RogerL

--
Roger Larsson
Skellefteå
Sweden

Roger Larsson <roger.larsson@skelleftea.mail.telia.com> wrote in message

Is it a good or a bad thing?

Cheers.

Elder.

Dan Kegel <dank-news@kegel.com> wrote in message


I am just evaluating how well would Linux (either 2.4 with preemption
and low latency patches or 2.6 with preemption enabled) perform for my
application. Worst case interrupt latency of 400us and thread
activation latency of 4ms are more than acceptable in my application.

Regards.

Elder.

Herman Bruyninckx <Herman.Bruyninckx@mech.kuleuven.ac.be> wrote in message news:<Pine.LNX.4.44.0404291542290.9591-100000@srv04.mech.kuleuven.ac.be>...
I had a quick look at it. My requirements are much more modest and I'd
rather use native linux resources instead. Still I will look at its
code for some tips.

Elder.

Wolfgang Mües wrote:

This method would get my vote. The "send a signal" approach is
workable, but it can be difficult to get right. This is especially true
if your application is already using a number of signals for other things.

YMMV...

John
--
John W. Linville
linville@tuxdriver.com

X-No-Archive:yes

A certain Mad@Spammers, of comp.arch.embedded "fame", writes :

What you'll need to do is create a device driver with an entry in /dev,
and then set up a poll()/select() call within it. These can be used to
inform a user space application that some data has arrived to be
processed.

Your user space code can open the device and use the above functions
which among other things provide the ability to block a thread until an
interrupt is received, etc. Much more elegant than signal processing.

The free book "Linux Device Drivers" covers this subject in detail.

--

"Jokes mentioning ducks were considered particularly funny." - cnn.com

X-No-Archive:yes

A certain Mad@Spammers, of comp.arch.embedded "fame", writes :

Supposedly the low-latency patch can give worst-case latency of around
150us, but you'd need to check out how this fits on your architecture.

--

"Jokes mentioning ducks were considered particularly funny." - cnn.com

X-No-Archive:yes

A certain Mad@Spammers, of comp.arch.embedded "fame", writes :
Keeps everything nice and simple. There is a consistent way of dealing
with hardware.

--

"Jokes mentioning ducks were considered particularly funny." - cnn.com

"Mad@Spammers" schrieb:
Look at rtc.c in the Kernel source. They provide a blocking read to the
application to have it wait for an event. Her some data is provided to
the application, too.

-Michael

Nope. Linux can't guarantee any worst-case latency at all (I did find
more than 100 msek with the low-latency patch in very rare instances).

-Michael

X-No-Archive:yes

A certain Michael Schnell, of comp.arch.embedded "fame", writes :
That's why I was quite careful not to use the word "guarantee".

Clearly if you need hard real time performance, you need to look at
another OS.

--

"Jokes mentioning ducks were considered particularly funny." - cnn.com

Chesney Christ <thegreatsuprendo@hotmail.com> says...
"Hard real-time means no surprises or silent failures as system
configuration changes or load increases. Deadlines will still
be met. For example, the worst case delay on a 1 millisecond
thread on the HP Pavilion Notebook (AMD K7) is 12 microseconds.
-http://www.fsmlabs.com/products/rtlinuxpro/


"RTAI's microkernel approach guarantees that the data-acquisition
task will take place on schedule, even while the previously acquired
and calculated result is written to disk."
-http://www.elecdesign.com/Articles/Index.cfm?ArticleID=3816&pg=2


"Lineo Solutions, Inc. (Lineo) demonstrated ... hard real-time
support with Linux .... Deterministic time metrics of the systems
demonstrated ... is as follows.

Interrupt Response Time 5 microseconds

Task Latency Time 4 microseconds

Periodic Task Latency Time 20 microseconds

Timer Clock Accuracy 1 microsecond, Jitter 1 microsecond)"

- http://www.lineo.co.jp/eng/news-even.../20040109.html


"RTAI - the Realtime Linux Application Interface for Linux ... lets
you write applications with strict timing constraints for your
favourite operating system."
-http://www.aero.polimi.it/~rtai/

"KURT-Linux: Kansas University Real-Time Linux: Microsecond timing
resolution and event-driven real-time scheduling..."
-http://www.ittc.ukans.edu/kurt/documents-noframes.html



--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
have an "impossible" engineering project that only someone like
Doc Brown can solve? My resume is at http://www.guymacon.com/

X-No-Archive:yes

A certain Guy Macon, of comp.arch.embedded "fame", writes :

http://www.aero.polimi.it/~rtai/docu...les/guide.html

"What is RTAI?

RTAI means Real Time Application Interface. Strictly speaking, it is not
a real time operating system, such as VXworks or QNX. It is based on the
Linux kernel, providing the ability to make it fully pre-emptable. "

Your serve.

[BTW, isn't RTAI a kernel - a microkernel - all by itself ? You could
say that this isn't actually Linux. Linux runs essentially as a process
above RTAI. This isn't necessary in an OS such as, for example,
Greenhills Integrity, which provides guaranteed latency and other
goodies.]

--

"Jokes mentioning ducks were considered particularly funny." - cnn.com