Lab 1 - Review of Assembly

The purpose of this lab is to review how to create MIPS assembly code with the SPIM simulator.

As a reminder from the syllabus, labs are due at Noon on Wednesday. You may work in groups of 1 to 3 students on this lab. Turn in one assignment per group, making sure to put the name of ALL group members in the Notes section of Moodle (or as a separate file uploaded for the assignment).

Part 1: Using SPIM on Sleipnir

Resources

SPIM is a MIPS simulator that can be run in either interactive or non-interactive mode. In interactive mode, SPIM allows you to step through your assembly code and observe the contents of the register file as the code executes. In non-interactive mode, SPIM will execute your code as a regular executable.

Interactive Mode

To enter SPIM, give the following command: 

        $ spim
This will enter the SPIM prompt, where you can give SPIM commands. For example, you can read a file containing MIPS assembly called "test.s" and run it with the following two commands: 
        spim> read "test.s"
        spim> run
When you are done with SPIM, you can return to the Sleipnir prompt with: 
        spim> exit
Non-interactive Mode

To just run your code, or display any errors found in your code, you can issue the following non-interactive SPIM command: 

        $ spim -f test.s

Part 2: Lab Assignment

The assignment is to create a MIPS program that can add 5 and 15 together and display the output. Build off the following program (also available as main.s) and the print.s program from CMPS 224: 
# A simple "Hello world" program

	.text
	.globl	main
	.ent	main
main:
	la	$a0,format1  # Load address of format string into $a0
	jal	printf       # Call printf

  la  $a0,format2  # load address of format string #2 into $a0
  li  $a1,50       # test %d format - load 50 into $a1
  jal printf       # call printf

	li	$v0,10       # 10 is the code for exiting
	syscall          # Execute the exit system call

	.end	main

	.data
format1: .asciiz "Hello world.\n"
format2: .asciiz "Register $a1 holds: %d\n"  
format3: .asciiz "%d plus %d is %d\n"
There are several important MIPS assembly instructions in this code snippet.

Instruction Description
la <destination>,<label> Load address (I type) - find the address of labeled data and load it into the destination register.
li <destination>,<immediate> Load immediate (I type) - store a constant value into a register
jal <procedure> Jump and link (J type) - Switch context to a named procedure. The printf procedure exists in the print.s file. It expect the format string to be in $a0, the first variable in the format string (optional) to be in $a1, the second variable in the format string (optional) to be in $a2, and the third variable in the format string (optional) to be in $a3
syscall Execute the system call indicated by the value in register $v0. The value of 10 is the code for exiting the program.

You can run this code with the following: 

     $ spim
     spim> read "print.s"
     spim> read "main.s"
     spim> run

Modify main.s to add the MIPS assembly instructions to load 5 and 15 to registers (the li instruction), add the two registers together to get the result, and call the printf function with the third format string.

Upload the modified main.s and a list with the names of the members of your group to Moodle to submit the assignment. If you finish in the lab on Tuesday, you can also show me your code to get credit for the group (please still have your group members' names in the code as it'll be quicker for me to look everyone up on Moodle that way).