Tuesday, December 01, 2009 1:32 AM,

A student writes:



	 Hi, Dr. Patt,
	      I am testing my checkerboard program and something seems off....
	          You provided us with two screen-shot samples, However, every 
	 time I hit a key it always comes out looking like example screen-shot one.
	 I can't seem to time it just right so that it interrupts while the 
	 checkerboard is still outputting a line.



How many times have you tried?



	 This has me thinking that maybe the keyboard interrupt is not allowed 
	 to interrupt a trap vector,



What does it mean to interrupt a trap vector?  Perhaps you mean a trap 
routine?
Why would that be the case?  No, it can.



	 since I am using TRAP X22 to output my  UT stringz.
	
	        Is my program fine or do I have to fix it.
	 Thanks
	 <name left blank, so I don't need to withhold it.  I prefer it not be 
	 blank>



I think you are just unlucky, unless you are doing something strange.
Others are finding that they get both screen shots.

If you have tried this a dozen times and you still only get screen shot 1, you 
may be doing something wrong.  The laws of probability, you know. In that 
case, you probably should check with a TA tomorrow.  

Yale Patt