At 08:38 AM 11/24/98 -0600, Wright, Robert B. wrote:
>I would also like to hear about any projects that incorporate java and rtl.
Ok, please excuse me if this is a bit long winded.... :-)
I'm currently working on two projects that involve RTLinux and Java.
Both involve real time instrument control. One is more deeply embedded
than the other. I.e. no monitor, keyboard, just an Ethernet connection.
The other actually has a GUI component but is being designed such
that the GUI component doesn't have to reside on the instrument doing the
acquisition.
Both designs use RTLinux and C to handle all the hard real time instrument
control as well as the acquisition. Several FIFOs connect this real time
layer with the Java code. One FIFO is for commands, one for responses,
one for the acquisition data stream. One FIFO is used for error propegation
from the real time layer up to the GUI layer.
Some fiddling is required to get Java to read data from the FIFO properly.
First, the byte order must be switched. Secondly, I found that, on occasion,
simply trying to read four bytes from the fifo wouldn't work properly. So
I had to counteract with a rather ugly kludge.
I've found that connecting the real time layer and the non-real time Java
layer in this way isn't very efficient for moving large amounts of data.
I'm currently exploring another possibility to improve performance.
Both designs use a PC104 interface board that I've designed and built to
offload
some of the processing overhead. A programmable timer on the board starts
a conversion. When the conversion finishes, an interrupt is generated. The
ISR (in the real time layer) reads the value, passes it to the data FIFO and
switches to the next channel to be serviced.
Both designs boot a pared down RTLinux system from an IDE flash disk. They
run from memory so the systems can be powered down without concern for
any shutdown.
Both are running from an Advantech single board computer measuring about
4"x6".
These SBCs contain ethernet, video, IDE controller, etc. So the overall
system is quite compact.
Overall, I'm quite impressed with the combination of RTLinux and Java. This
instrument needed to be networked. Using Java, I was able to jam in more
than was required in the tight timeline that was available. I've done similar
things in C, C++ and strongly believe that it was quicker & simpler to do
in Java.
Primary to this belief was a) the networking classes, and b) multi-threading.
Granted, it's not as fast as had it been written in C or C++. But I'd
probably
still be writing it had it not been for Java.
Originally, one of the projects was started in QNX, but was switched to
RTLinux
after a period of evaluation.
The instrument currently can handle multiple clients. Only one of which can
control the instrument. The others being only to interrogate the instrument
for things like: current instrument status, time remaining on current job,
current owner, etc.
Also, it was easy to build debugging into the design. Multiple concurrent
debug monitors can attach to the instrument via the network and receive
information on the current operation of the program, as well as thrown
exceptions and stack traces are reported to any debug monitor programs
that might be attached. So if a customer calls and says that the instrument
fails randomly once a week, I can attach via the net and monitor for that
intermittent failure.
One unit has been tested for a while in another department. When I asked
about any crashes or failures of the RTLinux system, all I got was blank
stares. It has never happened.
Also, I can update the software and reboot via the net. When they ask
for a change, I do the update, then phone them and ask what version
number is reported on the instrument's LCD panel to confirm the update.
They find this quite amusing. I find it very convenient, as I'm about
100km from where it's being tested.
Hope this was of some interest.
Regards,
Jim.
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