Sun, 17 Nov 2019, 23:04 correction to your PL3 grade

My students,

Due to a miscommunication between me and the TA responsible for grading PL3,
you received a 0 on test cases that failed because you tried to read a value 
from memory location x0000.  Memory locations x0000 to x2FFF are priviliged,
which means a user program can not access them except in very explicit
situations which we have not studied as yet.  

The case in point: The first word of each node of your linked list is a 
pointer.  Some of you tried to load from the address specified by the pointer 
instead of first examining the pointer to see if it contained the null pointer 
(x0000).  As a result, you got an access control violation since your user 
program does not have the right to access M[x0000].  The correct approach 
would be to first examine the pointer.  If it is x0000, you know you are at 
the end of the list and so you would not try to access M[x0000].  Since the 
concept of privilege is new to you, and I had told you in class that you can 
ignore access control violations (ACV) until we discuss them in class, I do 
not want any points taken off for this mistake.  Your PL3 submission is being 
regraded, and some of you will see an increase in your PL3 grade. 

Some of you know that we have provided a switch on the Simulator which kills 
the distinction between privileged and non-privileged in case some professor 
somewhere (certainly not at UT) wants to teach 306 without dealing with the 
issue of privilege.  However, at UT we want you to understand the concept of 
privilege.  So, although we have provided a switch that removes the distinction
between privilege and non-privilege, that switch is not for students in our 
classes at UT.

If, for some reason, you feel it is easier for you to set this switch to
remove the privileged/non-privileged distinction in order to get started
with the program, I will not tell you not to do it.  HOWEVER, please be
sure the program still works after you set that switch back to recognizing 
the distinction between privileged and non-privilege.  When we grade the
program, we will have the switch set to understanding the privilege
distintion.  And, in the future, not understanding that distinction will
result in an unpleasant cost.

Finally, I am sending you this message because I do not want you to be
discouraged by thinking you lost points for something that is probably not 
your fault.  You will not lose points for it.  But right now, you should
not be taking time to think about it.  Save that for after 5pm on Wednesday
after you have taken exam 2.  Between now and then, preparing for exam 2 is
what needs your attention.

Good luck with the exam on Wednesday.


Yale Patt