A lot of this stuff I plan to talk about tomorrow, but for those who are 
reading ahead, I will take a shot at it here.
	 
	 section 10.5.4
	 question 4.
	 Does device D interrupt C, or would it wait till C is done and then
	 interrupt B?

Interrupt-driven I/O is all about higher urgency devices pre-empting lower urgency
 devices.  Therefore, since D is not as urgent as C, it will allow C to finish.  Since
 it is more urgent than B, once C finishes, and the processor goes back to try to
 work on B, BINGO! C will pre-empt B.
		  
		  Text book p179 the question under 9.1.7
		  I didn't see any instruction in A.3 that looked like it would start the
		  clock.

For good reason.  If the clock were stopped, how would you fetch, decode, etc. that instruction?
     
     On a related note, p181, the halt instruction code.  Had a discussion

The work required to carry out the halt mechanism takes more than one 
instruction in the LC-2.  It is carried out by a trap service routine as 
you know, invoked by TRAP x25.  HALT is a mnemonic device, so you can not have to remember x25.

    with someone else about this.
    My thought was that the run latch is cleared at line 14 STI R0, MCR, and
    that once that was cleared it would stop processing instructions and
    therefore not go onto the 3 LD's and the RET that follow it.  (this

Absolutely correct.  Once you clear the RUN latch (bit[15] in the MCR), the clock stops, and
 no more processing occurs.

	   belief also comes from the fact that when I run programs in the LC2, at
	   the end the PC has always ended up really far away from where my code
	   has started)

Good observation.  You are in the TRAP x25 service routine.

     The opposing viewpoint, all those instructions up until the RET are part
     of the HALT instruction, therefore the clock doesn't stop until after

No, there is no "HALT instruction."  There is a TRAP x25 instruction which calls the trap service
 routine to halt the machine.

    the 3 LD's and RET have been completed.  The HALT instruction is really
    one instruction so it can't stop until it is done with all the parts of
    it.
     
     Which kind of brings me back to the p179 text book question, if the
     clock is stopped, the computer would no longer be able to run
     instructions, right?  

Right.

	So I'd guess that the only way to make the
	computer start running things again is some sort of manual method (i.e.
	reset button)

Right again.
       
       This is probably cutting it close to the test.but I don't actually
       expect these things to be on it..
       Maybe I'll be pleasantly surprised tomorrow.  ^_^
        
This stuff was not on the second test, as you all know.  However, it is critically important stuff.
  We will talk about it between now and the final and you will see it again, and again (319K), and
 again (360N), and again (345L)....

Yale Patt

     <<name withheld to protect...>>