Here are announcements on the SP and the FP:

BUG in UT PCSPIM's display of the stack pointer:

   #Something strange and interesting happens about the $sp in 
   #PCSpim.  The starting $sp is always = 7fffeffc
   #If I step through (F10) the program, the final $sp=7fffeffc
   #But if I run it: the final $sp=7fffef08

There is a quick work-around for this for P4 if you want to just "run" a prog:
use "F10" to step through the first few instructions until you reach main, 
then select the simulator continue option...
( you will get the $sp value of 7fffeffc, assuming your program is right )


ANSWER TO CONFUSION ABOUT WHERE IS THE FP????  Answer:  register 30
The User's manual tells us that the frame pointer is Register 30, but the
PCSPIM display shows it with a nickname of "S8".  However, you can still
program with it using the nickname "fp"

Thanks, Chris Edmondson