Fri, 30th Oct 2015, 03:34 Re: Some help for lab 2 --- Ooops, two typos!

My students,

Greetings from California where I am here for two days.  In my haste to
send you the "hints" email from the airplane, I made two typos which one
of my TAs caught.  Hints with typos often do more harm than good, so here
is my email again, this time with the typos corrected.  And an extra
snippet thrown in.

> On Thu, Oct 29, 2015 at 7:45 PM, Yale N. Patt <patt@ece.utexas.edu> wrote:
>
> > My students,
> >
> > In class late on Wednesday, I tried to give you some hints that would help
> > you with lab2, but we ran out of time.  So I thought I would provide this
> > email.  Feel free to ask your TA anything about it in discussion tomorrow,
> > and/or any of the TAs during office hours.  For those of you who had
> > discussion session today and want to simply show up to another session
> > tomorrow, please do so.
> >
> > What I am providing below are a number of snippets of LC-3 code, each of
> > which does something that you might find useful in writing your program to
> > solve the problem of lab2.
> >
> > Recall in class, we identified two locations: VALUE and ADDR.  VALUE was to
> > contain a value that we were going to check the linked list to see if it
> > exists.  ADDR was to contain the address of the list head.
> >
> > VALUE .FILL <<the value>>
> > ADDR  .FILL x4000  ; If the listhead is at location x4000
> >
> > Both of these will come after the TRAP x25 in your program.
> >
> > Now then, what does the following snippet of code do?
> >
> > LD R0,VALUE
> > NOT R0,R
> > ADD R0,R0,#1

First typo.  It should be:

LD R0,VALUE
NOT R0,R0
ADD R0,R0,#1

> > It would be good to look at the figure of the linked list at the bottom of
> > the lab assignment as you follow these snippets of code.  What I would like
> > you to do is see what each does with respect to that figure.
> >
> > LD R1,ADDR
> > LDR,R2,R2,#0

Second typo.  It should be:

LD R1,ADDR
LDR R2,R1,#0

And, to make up for it, one more snippet:

ADD R1,R2,#0
LDR R2,R2,#0

Good luck getting the lab done by Sunday night.

Yale Patt


> > Next,
> >
> > LDR R4,R2,#1
> > ADD R4,R4,R0
> >
> > Next,
> >
> > LDR R5,R2,#0
> > STR R5,R1,#0
> >
> > In the lab we do not have a single VALUE.  Instead we have a second linked
> > list
> > where each value (i.e., drivers license) in the second linked list has to
> > be
> > checked against the values in the first linked list.
> >
> > Finally, you need to put those nodes that are present in both lists at the
> > end of a third linked list, whose listhead is in location x4002.
> >
> > Suppose you have just discovered a person who is both a millionaire and a
> > professor.  You have already removed him/her from both linked lists.  Now
> > you
> > have to insert him/her at the end of the third linked list, whose listhead
> > is
> > at x4002.  Let's say that the node at x8050,x8051 has just been removed
> > from the two lists.  You have a register pointing to it, say R5.  That is,
> > R5 = x8050.  You also have a register pointing to the node you previously
> > last added to the third list.  Say that register contains xB000.  Then you
> > know the contents of xB000 = x0000.  Your job is to put x8050 into location
> > xB0000, and x0000 into location x8050, thereby inserting this node at the
> > end of the third list.
> >
> > I will leave it for you to write the snippet of code to do that task.
> >
> > By the way, when your program starts, there are no elements in the third
> > list.  Therefore what are the contents of x4002, the listhead for the third
> > list?
> >
> > Good luck with lab 2.
> >
> > Yale Patt
> >
> >