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JMRI: Debugging Your Installation

This page presents an orderly method for debugging problems that first appear when JMRI/DecoderPro is installed.

Even if you're an experienced debugger, we suggest you work your way through these steps in order. That way, if all else fails and you have to call for help, most of the initial stuff will be known to be OK.

Step 1: Do you have Java installed?

Start by making sure you have an appropriate version of Java on your system by typing

java -version

at a command prompt and looking the message that produces.

JMRI® version 4.2 requires Java 1.8.
Version 3.10.1 requires Java 1.6 or later.
Version 2.14.1 requires Java 1.5 (or 1.6 if you wish for drag & drop).
Version 2.12 requires Java 1.5 or later.

If you get a message about "command not found" or similar, then Java is not properly installed; consult the install pages for your Mac OS X, Linux, Windows computer for advice on how to fix this.

Step 2: Does the program start?

Try to start DecoderPro. (The method to do this depends on whether you are using a Mac OS X, Linux, Windows computer; see the relevant page)

This tests whether the basic installations of Java and JMRI are OK. If the program doesn't start up and run at least as far as producing it's title screen and menus, there's something wrong with either the JMRI installion, or perhaps with the Java installation.

In that case, look for console messages that might describe what went wrong. Those appear in different places:

Mac OS X
In the "Console" application, found in the Applications/Utilities folder, which you have to start
In the shell window from which you started the program
In the "Java" window; you might have to find this in the start bar at the bottom of the screen and expand it

See if the messages tell you anything useful about missing pieces, etc. If not, cut and paste them into an email to the jmriusers discussion list, and somebody will help you figure out what went wrong.

Step 3: Are the Java communications libraries present?

Once the program is running, pull down the 'Edit' menu and select the 'Preferences ...' item. This opens the preferences panel. Select the proper protocol for your layout.

At this point, do the names of one or more serial ports appear in the selection box on the right?

If not, does your computer actually have any serial ports? You can't use JMRI without them (Well, you can use the program, but you can't communicate with a layout). You need to either get a serial port, or install a USB-serial adapter.

But if you have one or more serial ports, and they're not showing, this could mean that the Java communications libraries aren't properly installed. Check for error messages (see the note on how to do this in Step 2 above) If you see messages about "failed to load" or "missing class", then the communications libraries weren't found.

To fix this, please see the system-specific pages for your Mac OS X, Linux, Windows computer.

Step 4: Is the communications port configured right?

For most protocols, you have to configure the baud rate, and perhaps other options. These have to be set consistently with the layout hardware for communications to be possible.

Step 5: Can the program talk to the layout?

The method to check whether the program can talk to the hardware of your layout depends a little bit on what you have installed. Basically, you want to command the system to do something that you can see. See if each of the following works:

Step 6: Can decoders be programmed?

Typically, this is what people want to do first. But by going through the prior steps, we know that communications between the program and the layout are fine, and we're just working through the last details now.

To check this:

If all goes well, you'll get a succesful read of the same address you saw previously.

If not, check for a message. Among the possibilities are:

No Locomotive Detected
No Acknowledge from Locomotive
These comes from the command station. It means that the program was able to talk with the command station OK, but the command station could not talk to the locomotive. Go back to reading with the throttle and make sure what works. If it does, try selected different programming modes (e.g. paged, direct, etc) in DecoderPro and retrying the read.
Timeout talking to command station
This means that the program didn't hear any response from the command station when it requested the CV to be read. This is unexpected, because we found that communications to and from the command station were OK in step 5. Check that step again. And look for error messages that might provide a clue (see step 3 for info on how to do that)