Xterminals

There are about 45 Xterminals connected to newt. 35 of these have been purchased by individual departments within the School, and the remaining ten are for general use. If you find that it is difficult to get access to an Xterminal, then consider lobbying an academic in your Department to write a grant application to buy one, or assist Michael Ashley or Chris Hamer in writing a Major Equipment Grant.

Using an Xterminal

Fixing a stuck Xterminal

It is important not to reach for the off-switch as a first attempt to fix a recalcitrant Xterminal. This is because newt expects the Xterminal to be in a particular state, and if you turn the terminal off and then on, the state has been lost. newt may be waiting for input from a window that no longer exists.

Start by looking for the tell-tale flashing (once a second or more) of an LED on the keyboard (note: ths applies to the NCD Xterminals only--the Labtam and Labtek terminals have an internal LED). The LED flashes each time that the Xterminal is sent data on the ethernet (usually the flashes come from Apple Macintoshes that have been incorrectly setup and are broadcasting to everyone on campus). If the LED is not flashing then either

• there is a break in the ethernet somewhere, or the ethernet is incorrectly terminated (see the section on ethernet problems),
• the Xterminal is off, try turning it on ...
• the Xterminal has not been booted properly.

The final problem needs further explanation. When you first turn on an Xterminal it knows nothing about how to interpret the X-protocol (which is what newt speaks to it), all it knows is how to establish a simple connection to newt for the purposes of downloading its own operating system. The Xterminal performs the following steps immediately after switch-on:

(1)

--Checks its internal memory. If there are problems at this stage an error message will appear, and you should contact Michael Ashley who has spare memory boards available.

(2)

--Broadcasts a message on the ethernet asking someone to tell the Xterminal what its ethernet address is. newt, tycho, or isaac should respond. If the terminal can not find its address, then either the ethernet is faulty, or one of the computers is down.

(3)

--Downloads its operating system. This process is indicated by a series of dots appearing on the screen (NCD Xterminals only). The dots should appear rapidly and at a uniform rate (with maybe one or two pauses) for about 1.5 screen widths (more for a colour Xterminal), taking a total time of 15 seconds or so. If the dots appear slowly, and with many hesitations of five seconds in length, then there is probably an ethernet problem, most likely due to electrical noise from a piece of lab equipment, or to someone having over-extended or incorrectly terminated the segment of ethernet that you are on (try looking at the back of the Xterminal, if the ethernet is not connected via a tee-piece directly to the terminal, then a wiring error has been made). You should track down the source of the problem, otherwise your Xterminal performance will be degraded.

(4)

--The Xterminal now downloads a configuration file that sets numerous internal parameters.

(5)

--A few fonts are now loaded. During this step and the preceeding one, the Xterminal displays on the screen what it is doing. If there are any errors in loading fonts you should turn off the Xterminal and start again. After the cursor font is loaded, the Xterminal's screen shows a uniform grey pattern and is ready to accept X-protocol commands.

What happens next depends on the state that newt thinks the Xterminal is in. If newt thinks that you have a login session underway, then it is possible that nothing will appear on the screen. If the Xterminal had been logged out of correctly before it was last turned off, then newt will realize (after a short delay, less than one minute) that the Xterminal is now available again, and will display a login box (generated by a program called xdm). If the terminal still displays a blank grey screen, try the following

• Press COMPOSE-SETUP (NCD Xterminals only). This will cause the Xterminal to display a menu of local commands. Move the mouse pointer until it is over the ``Restart Session'' button near the top right corner, and press the left-most mouse button twice. Then click on the ``Done'' button near the bottom right. This may result in the login box appearing.

It may also be useful to have a look in the DIAGNOSTIC SESSION window accessible from the COMPOSE-SETUP menu (note that COMPOSE-SETUP only works with NCD Xterminals, and only after you have booted the Xterminal from newt). Normally this window will display information concerning the fonts that the terminal has loaded. If strange error messages appear, they may give you a clue as to the problem. Also, try looking at NETWORK STATISTICS, and examine the number of ethernet errors such as collisions as a fraction of the total number of ethernet packets received/transmitted. The fraction should be very small, perhaps 0.01%. If it is high, it usually points to a problem with noise on the ethernet. You can select a button to clear the current statistics in order to compare the current error rate with the long term average.