Sun, 10 Feb 2013, 20:18

A student writes:

> Dr. Patt,
> 
> For the RTI instruction, I am guessing we are supposed to ignore the
> operation regarding the PSR, because there isn't a PSR latch. So I am
> currently processing RTI as:
> 
> PC = MEM[R6]
> R6 = R6 + 4;
> 
> As opposed to:
> 
> if (PSR[15] == 1)
> PC = MEM[R6];
> R6 = R6 + 2;
> TEMP = MEM[R6];
> R6 = R6 + 2;
> PSR = TEMP;
> 
> Should I be doing anything differently for this instruction?

Yes, you should not be wasting time doing anything to handle RTI
instructions.  Have you read Clarification #2 associated with the 
Lab Assignment.

> Also, what do we do if a LDW address is not aligned?
> Do we just skip that instruction, exit with an error message, load that
> word, or load half of that word and half of the next word?

Have you read Clarification #3 associated with the Lab Assignment.

> Thanks,
> <<name withheld to protect the student who misplaced the Clarifications>>

Perhaps I should not be so abrupt with a student's questions, since I do
want to encourage you to ask me or the TAs when you do not understand 
something.  But I would like to think your first step is not to ask, but
rather to see if you can figure it out for yourself.  And the Clarifications
should help.  That is why we wrote them.  In this case, Clarifications 2 and 3
so clearly spell out the answers to the student's questions that it is hard
for me to believe that a UT senior or graduate student could read those
answers and still have a question.  Perhaps someone will enlighten me.

In the meantime, I will work on being less harsh, and also wish you good luck
on getting the lab done before the deadline.

Yale Patt