RXTX Bug

A very, very small bug. I've never actually felt fired up enough to fix some open source code. Not good enough really, I use open source stuff by preference. I've sent money to some projects I've felt particularly grateful to, but not enough money and not enough projects to stop me feeling slightly guilty! What's the problem? I want RXTX to recognise my USB serial (or is it a modem?) device on ttyACM0. The advice in the documentation is to put an entry in gnu.io.rxtx.properties to tell RXTX which unusual ports you want. I did that, and got nowhere. I recompiled the code (Hooray for Open Source!) with the debug flag on, and got this:

The file: gnu.io.rxtx.properties doesn't exists.
java.io.FileNotFoundException: /usr/local/java/jre/lib/ext:/usr/java/packages/lib/ext/gnu.io.rxtx.properties (No such file or directory)

I'm so happy I could jump for joy - an easy bug! Looks like the code is appending the filename to a colon-separated list of paths, instead of to each path in the list in turn. Ooh, now that I look at it... maybe too many people have edited this code... it's a bit confused. The gnu.io.rxtx.properties file contains some handy properties, but the code replaces the entire System properties with the one or two in the file. That can't be right. There's even a comment at the head of the ChangeLog for 2.1-7pre22 that says not to overwrite System properties.

I just want to get the piece of code I'm interested in working. Doing anything else strikes me as rude, so I'll press on. The fix is to just extract the necessary data from the properties files - note that there could be more than one, thanks to the previous change.

It's getting worse!

OK, so I made the initial change to make sure those properties were being read properly. Now there's a function in the native library 'testRead' that says ttyACM0 fails. In some way. So I want to add some debug comments to that C code. But RXTX 2.1-7r2 doesn't build properly! When you extract the tarball, it won't make:

make: *** No rule to make target `i686-pc-linux-gnu/librxtxSerial.la', needed by `all'. Stop.

I don't know why!
But it's okay, I was just doing the usual ./configure, make, make install process. The problem goes away if, with a freshly extracted source, you:

aclocal
./autogen.sh
./configure
make
make install

make install fails at this point with the error:

libtool: install: `i686-pc-linux-gnu/librxtxRS485.la' is not a directory

Again, who knows why. I do know that the error is caused by the absence of a value being assigned to RXTX_PATH in Makefile. Editing Makefile, and editing the line so it assigns RXTX_PATH to the path to where the JRE's ext libraries are kept will allow make install to finish. For me, it's:

RXTX_PATH = /usr/local/java/jre/lib/i386/

Phew! I can finally compile and install all my changes. There's another problem in the Makefile that causes (on my system) the newly created RXTXComm.jar file to end up in the '/' directory. Locate and change the JHOME assignment to something useful for your system. For me it's:

JHOME = /usr/local/java/jre/lib/ext/

Such a slow process. Now it's my bedtime. testRead is rejecting /dev/ttyACM0 at the same place it rejects all the other non-connected devices:

do {
fd=OPEN ( name, O_RDWR | O_NOCTTY | O_NONBLOCK );
} while ( fd < errno="=" ret =" JNI_FALSE;">

The same code accepts /dev/ttyUSB0 - the only serial port connected to my laptop. But I can't establish a connection to the scope over the USB serial lead. My head hurts. One last try, USB serial from Windows. Nada. Serial works fine from the desktop, so it's a USB serial issue. Too tired to think.
Night!