Java and LXRT/COMEDI

Paolo Mantegazza mantegazza at aero.polimi.it
Fri Oct 29 09:34:22 CEST 2004


Kenneth Jacker wrote:
> As long time members of these list know, I have used RTAI (RTLinux at
> first) and COMEDI for many years in my undergraduate/graduate
> "real-time systems" course.  Though I and some graduate students have
> "experimented" with LXRT, most of our projects have used RTAI, kernel
> modules and Tcl/Tk -- *not* LXRT.  
> 
> Next semester I am considering using LXRT and COMEDI with Java as the
> GUI front end instead of Tcl/Tk.
> 
> I know Java works using the "kernel modules approach" where multiple
> threads interact with RT FIFOs (to avoid blocking "issues") and the RT
> side is written in C.
> 
> However, Paolo and others are encouraging the use of LXRT over the
> deprecated "kernel modules approach" for reasons that have been stated
> many times on the RTAI list.
> 
> It appears that the LXRT/Java approach would require me and my
> students to write Java-callable routines in C for the actual, time-
> critical RT code.  These "methods" themselves would invoke
> rt_make_hard_real_time(), rt_make_soft_real_time(), etc., and have to
> be written following the JNI (Java Native Interface).
> 
> Compared to using the multiple thread/kernel modules approach
> described above, this would be a *lot* of work (unless someone else
> has already done it) and require learning JNI.  Also, I'm not sure
> there wouldn't be problems (scheduling, timing, etc) with the JNI
> "RT methods" interacting with the Java virtual machine.
> 
> 
> Have others used LXRT, COMEDI and Java *without* kernel modules?
> 
> I am *most* interested in hearing others' experiences, thoughts,
> suggestions, and/or comments ...
> 

Whatever you'll do recall that you are not required to change your way 
of working just because of LXRT. LXRT can do them all. If it is 
confortable to stay in kernel space stay there.

Sorry to be picky with this but is important that people know that an 
LXRT only RTAI is not going to force anybody to do what (s)he is doing 
differently than before. You will not even notice that there is just LXRT.

Paolo.

Paolo.





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