MIPS Assembly Language Programming

1
MIPS Assembly Language Programming
CDA 3101 Discussion Section 03
2
Outline

• MIPS simulator PCSpim
• Problems from textbook
• 2.29, 2.30

3
PCSpim

• Installation
• From the textbook CD
• From the internet
• http//www.cs.wisc.edu/larus/spim.html

4
Writing A Basic Program

• Lets start by writing a program that sums all
  the numbers between 1 and 10.

int main() int i 10 int sum 0
do sum sum i i i - 1
while( i ! 0 ) return sum
5
PC Spim
6
PC Spim

• Note the top window it contains the state of
  all registers.

7
PC Spim

• The button on the top right runs the program to
  its end, after you click OK on the dialog box.
  Note that you wont see the register changes
  until the program ends.

8
PC Spim

• Click this menu item to reinitialize PC Spim
  its like rebooting your computer. Its often
  necessary to click Reload to run your program
  again.

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PC Spim

• Click this menu item to change settings for the
  emulator.

10
PC Spim

• Click this menu item to change settings for the
  emulator.
• Sometimes its helpful to uncheck General
  registers in hexadecimal so that you can read
  values as regular numbers.

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PC Spim

• Click the button that looks like a hand to set
  breakpoints. The program will stop running at
  positions you indicate, and wait for your
  authorization to continue upon reaching said
  point. You will also see the register values
  updated.

12
Understanding MIPS code

• Problem 2.30
• Add comments to the following MIPS code and
  describe in one sentence what it computes.
• The code processes 2 arrays and produces a value
  in v0. Each array consists of 2500 words indexed
  0 through 2499, the base addresses of the arrays
  are stored in a0, a1, and their sizes are
  stored in a2, a3. What will be returned in v0?

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Understanding MIPS code

• Problem 2.30
• sll a2, a2, 2
• sll a3, a3, 2
• add v0, zero, zero
• add t0, zero, zero
• outer add t4, a0, t0
• lw t4, 0(t4)
• add t1, zero, zero
• inner add t3, a1, t1
• lw t3, 0(t3)
• bne t3, t4, skip
• addi v0, v0, 1
• skip addi t1, t1, 4
• bne t1, a3, inner
• addi t0, t0, 4
• bne t0, a2, outer

14
Understanding MIPS code

• Problem 2.29
• Add comments to the following MIPS code and
  describe in one sentence what it computes. Assume
  a0, a1 are input, initial value a, b v0 is
  output.
• a0 input a a1 input b v0 output
• add t0, zero, zero
• loop beq a1, zero, finish
• add t0, t0, a0
• sub a1, a1, 1
• j loop
• finish addi t0, t0, 100
• add v0, t0, zero