IEEE-488 Device Image Grabber

This applet obtains and displays screen images from IEEE-488 (GPIB) devices. Scroll to the bottom of this page to see a description of the controls and error messages.

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Controls

The control elements, from left to right, are:

Reboot Button

The Ethernet/GPIB controller occaisionally gets confused and needs to be rebooted. Pressing this button will pop up a panel requesting confirmation of the reboot operation. Confirming the operation will result in the controller currently selected by the Controller Selection Menu item being rebooted.

Warning: Rebooting a controller severs the connection to all devices currently in use on that controller. This includes devices in use by others, so take care that you don't interfere with others using the controller.

Controller Selection Menu

With this menu you select the Ethernet/GPIB controller to which your device is connected.

Device Selection Menu

With this menu you select the number (0 to 30) of the device from which you want to grab an image.

Shutter Button

Pressing this button takes a snapshot of the screen of the currently-selected device. If the screen image is successfuly captured it will be displayed below the row of control elements and the print button will be enabled. Failure to capture an image will produce an error message.

Note: It can take 20 seconds or more to obtain a screen image from some devices.

Print Button

Pressing this button will print the currently-displayed image.

Save Button

Pressing this button will bring up a file-save panel. The image will be saved in Portable Network Graphics (.png) format.

Error Messsages

There are several places where communications can break down. Some of the more common error messages, and the error conditions they describe are:

IEEE-488 ONC/RPC Exception: ONC/RPC portmap failure

This usually indicates the the applet is unable to connect to the Ethernet/GPIB controller. Verify that the controller is connected to the network and that its Receive indicator flashes as packets arrive from the network.

IEEE-488 I/O Exception: VXI-11: I/O timeout

The applet was able to communicate with the Ethernet/GPIB controller, but can not communicate with the specified device. Check that the cable between the device and the controller is properly connected and that the device's IEEE-488 address (0-30) is as expected.

IEEE-488 I/O Exception: VXI-11: I/O error

This message usually indicates that the IEEE-488 address of the selected device (0-30) is actually the address of the IEEE-488 controller.

access denied (java.net.SocketPermission xxxx.xxx.xxx connect,accept,resolve)

Applets must be given permission to connect to Internet hosts other than the host from which they were loaded. This error message indicates that the applet has not been granted permission to connect to the specified Ethernet/GPIB controller. Contact your system administrator or add the permissions to your personal java security policy file.

Print Permission Error

This error message indicates that the applet has not been granted permission to queue printer jobs. Contact your system administrator or add the permissions to your personal java security policy file.

PropertyPermission user.home read

FilePermission xxxx read

RuntimePermission modifyThread

This error message indicates that the applet has not been granted permission to perform the file I/O operations required to save image files. Contact your system administrator or add the permissions to your personal java security policy file.

Security Policy Configuration

You must grant special security privileges to the scope camera applet to allow it to perform properly. These permissions can be granted from the system-wide java security policy file or from your own personal security policy file. On Unix (Linux, Mac OS X) machines your personal security policy file is ~/.java.policy and on Windows machines your security policy file is C:\Windows\Profiles\username\.java.policy. Unfortunately the Engineering laboratory computers now clear this file each time you log out so the security configuration on these machines has been extended to use H:\java\java.policy as well.

To grant all required privileges to the scope camera applet add an entry like the following to your security policy file:

grant codeBase "http://www.engr.usask.ca/classes/EE/scopecam/-" {
    permission java.net.SocketPermission "eegpib01.usask.ca", "connect,accept";
    permission java.net.SocketPermission "eegpib02.usask.ca", "connect,accept";
    permission java.net.SocketPermission "eegpib03.usask.ca", "connect,accept";
    permission java.net.SocketPermission "eegpib04.usask.ca", "connect,accept";
    permission java.lang.RuntimePermission "queuePrintJob";
    permission java.util.PropertyPermission "user.home", "read";
    permission java.lang.RuntimePermission "modifyThread";
    permission java.io.FilePermission "<<ALL FILES>>", "read, write";
};

1. You'll need to replace the http://www.engr.usask.ca/classes/EE/scopecam/- with the URL from which you're loading the applet.
   
2. You need the the queuePrintJob entry only if you want to be able to use the applet Print button.
   
3. You need the the final three entries only if you want to be able to use the applet Save button. If you want to restrict the locations to which the applet can save files, change the <<ALL FILES>> entry. For example, if you replace <<ALL FILES>> with C:\TMP\- the applet will be restricted to to saving files in the Windows temporary directory.

Configuration

The java applet uses the values of three parameters to form the domain name of the GPIB/LAN adapters. The parameters and their values, if not specified in the HTML which invokes the applet are:

The parameter values are used to form the name of the GPIB/LAN adapter as lanAdapterBasename##lanAdapterDomain where ## begins at 01 and continues upwards until the lanAdapterCount has been reached.