Summary: VisAD on the iPAQ/SavaJe is possible, but it's best not to put
your application into a JAR file. I hope the following suggestions could
save anyone else trying to to run VisAD under SavaJe some time:
1) Copy all data and class files to your iPAQ - don't try to use a
network filesystem for data or class loading.
2) Don't use the SavaJe suggestion of bundling your application into a
JAR file.
3) Surprise yourself at how usable a VisAD application can be on a
handheld device which doesn't even have hardware floating-point! The
application I use produces a visualisation of a 35 KB netCDF file
representing wave heights in the Mediterranean sea. VisAD runs on my
iPAQ about 4-5 times slower than on my 400 MHz PII PC - not stellar
performance, but still acceptable.
Background
The research project I am working on is exploring distributed
collaborative visualisation and component software technology. We have
recently bought Compaq iPAQ PDAs for each of our project team and I saw
the prospect of running our VisAD application on such a constrained
device as an exciting challenge. (More details of the research project,
VisualBeans, are available at http://www.acu.rl.ac.uk/VisualBeans/).
Procedure
I chose the SavaJe operating system, http://www.savaje.com, rather than
staying with Windows CE/Pocket PC, as SavaJe supports Java 2 Standard
Edition. My application only requires Java2D graphics, which is well
supported under SavaJe. Installing SavaJe on the iPAQ was a simple
process using the GUI installer which SavaJe provide. I backed-up
Windows CE to allow for possible re-installation later.
I had problems getting a network filesystem working reliably under
SavaJe. One can either use a web filesystem, using HTTP, or SMB mounts.
I have found the latter to be more reliable, although the implementation
in SavaJe uses NetBEUI as a transport, so I had to re-install NetBEUI on
my desktop PC. (SavaJe appear to be using the jCIFS package from
http://jcifs.samba.org - this only runs under NetBEUI as far as I can
tell, not TCP/IP).
My attempts at using the Web filesystem worked for files with simple
pathnames, but longer pathnames were corrupted, possibly due to my
mis-configuration of the Apache web server (I tried this under both
Windows NT and Linux). It appears that Apache was returning a directory
listing to the iPAQ which contained HTML character entities in the
pathnames - i.e. more suitable for presenting to a user reading a HTML
page - this particularly confused the SavaJe class loader.
My *recommendation* is not to use a network filesystem for class
loading. Instead, copy all class files and other resources directly to
the RAM filesystem on the iPAQ. On my 64MB iPAQ, there is around 48 MB
available to be shared between program memory and data files. My
application takes about 60 KB and the visad.jar file I was using is
around 4.5 MB. I was able to run two datasets into my application
without running out of space.
The SavaJe documentation on running Java applications
(http://www.savaje.com/support/docs/doc/run_java.html) suggests that you
bundle your application into a JAR file whose manifest includes entries
for 'Main-Class:' and 'Class-Path:' I didn't find running my
application from a JAR file to be reliable - my application would start
to run, but quickly run out of free memory and usually end up in a
system crash. If I was quick enough, I could start the program, then (in
another window) remove the application JAR file - this appeared to free
some system resources and allow my application to behave as expected.
Not what you would call intuitive.
Instead, I copied the directory containg the package class files over to
the iPAQ.
The equivalent of CLASSPATH under SavaJe is the environment variable
'base'. This normally allows one to include references to HTTP or SMB
filesystems with the syntax http:// or smb:// - however, the syntax for
accessing directories or JAR files in the local filesystem uses the
syntax file:/// - that's three occurences of the slash character, which
caught me out a few times.
In my case, I did the following:
set base=file:///ramfs/users/USER,file:///ramfs/users/ijj/visad.jar
To invoke the Java application, I needed to use the 'run' command with
the '-nosm' flag. This specifies running without a security manager -
otherwise, access to the local filesystem for e.g. reading data files is
not allowed. The run step looks like:
run -nosm package.MainClass
where the 'package' is the directory containing the class files in the
Java package within the USER home directory.
Results
My application runs on the iPAQ! A testiment to Java portability,
VisAD's effiency, and SavaJe's J2SE environment. The application is
quite usable, despite the hardware constraints (no H/W FP, slow-ish CPU
and lack of physical screen real estate). The SavaJe environment has
some nice features, such as rapid switching between windows with short
presses of the iPAQ 'Record' button, and allows one to rotate the screen
by long presses on the 'Record' button - each long press rotates the
screen by 90 degrees. The spec. also claims that one can pan around a
virtual screen if the application windows are larger than the physical
screen - I haven't had a chance to try this yet.
Ian Johnson,
Business and Information Technology Department,
CLRC Rutherford Appleton Laboratories.
