Hi Erwin and all,
Got lots of responses, thanks all for making this list so helpful and
informative.
Since both you and Tomek adviced me with LXRT under RTAI, especially your
case is very similar to mine: have a large crosslinked object model, need
to perform real time actions on the model (actually, touch it) and display
those actions,... I shall spend some time to investigate LXRT. Thanks.
Well, a few more questions:
What do you mean to promote a userspace process to a Realtime task?
Besides, do you know any function of linux that provides better resolution
than time(0) of #include<time.h> ? and what is the header file to
include?
If it turn out that LXRT fails for my purpose, one alternate is to decople
the graphics display of the model and location of the action from the
real time action itself (through FIFO) . However, this leads to another
issue, is it possible to use list of lists (i.e., pointer of pointers)
with real time linux? As I can use the simplest way to model the objects:
their center-lines, with each line contains a list of points that it
travels through.
Thanks in advance.
Dingrong Yi
On Sun, 14 Jan 2001, Erwin Rol wrote:
>
> You could take a look at LXRT, which is part of RTAI, that makes
> it possible to promote a userspace thread (or process) to a Realtime
> task. Due to the internal setup you will loose a few usec in latency,
> but
> i haven't seen more than 30usec latency (appart with my S3 card and
> XFree
> 4.0, but thats an other story). Also it will not be posible to make anny
> system calls from the promoted threads/processes, but there is also
> being
> worked on.
>
> I use it because i have a large crosslinked object model , and need to
> preform
> certain actions on the model in real time ( 40 times a second ), and
> display
> those actions at the same time. Because the displaying and the realtime
> actions
> not change the model there is no need for locking, because when you lock
> it from
> non realtime you of courrse loose realtime behavior in the realtime
> task.
>
> So becarefull when you start to need locks on the model , you will
> probably
> loose realtime, when your not carefull.
>
> RTAI can be found at www.rtai.org
>
> - Erwin
>
>
>
> Dingrong Yi wrote:
> >
> > Hello all RTLinux users and developers,
> >
> > I need to schdule a procedure by a timer at every (around) 1 ms. I
> > set the time interval of the XtAppAddTimeOut to be 1ms. But I am
> > uncertain is the resolution of linux timer is such fine or not? Tijs
> > suggested to modify parameter HZ of
> > /usr/src/linux/include/asm-i386/param.h to 1024 for a 2ms timing
> > (attached at the end). Does it mean if modify HZ to 2048 may get a 1ms
> > resolution timing? If so, what should I do after this modification so
> > that this modification may be effective?
> >
> > I am booting with RTLinux-2.0. The reason why I do this high frequency
> > (1000 Hz) task in linux instead of RTLinux is because this task need to
> > use lots of graphics, big memory (60M) for object modeling, etc which are
> > cubersome to do in RTLinux.
> >
> > Thanks in advance.
> >
> > Dingrong Yi
> >
> > > > Hi!
> > > >
> > > > In RT-Linux Manifesto author writes:
> > > >
> > > > "Standard Linux takes up to 600 microseconds to start a handler and
> > can
> > > > easily be more than 20 milliseconds (20,000 microseconds) late for
> > a
> > > > periodic task."
> > > >
> > > > Is it possible to have 2 miliseconds ? I want to control very fast
> > robot
> > > > from rt-linux box.
> > >
> > > This works for x86 only:
> > > Try using #define HZ 1024 or some other high number in
> > > /usr/src/linux/include/asm-i386/param.h
> > >
> > > Usually it's 100 and that accounts for the (what I thought were 10) 20
> > > ms.
> > >
> > > Note that this breaks some programs like 'top' and 'ps'
> > >
> > > --
> > > Tijs van Bakel, <[EMAIL PROTECTED]>
> >
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