CSCI2500-Lab 4 Solved

Checkpoint 1: Start by installing the latest version of SPIM, which is a MIPS simulator.

The URL is: https://sourceforge.net/projects/spimsimulator/files/.

After installing SPIM, download the helloworld.s code from within Course Materials in Submitty, then run the code in SPIM. Within the spim interface, enter the ‘?’ character to get help in loading a program, running it, stepping through it, etc. Of particular interest are the run, step, and print_all_regs commands.

Also, in general, refer to Appendix A of our textbook and use this URL as a reference for how to write MIPS programs for this environment:

http://logos.cs.uic.edu/366/notes/mips%20quick%20tutorial.htm.

And refer to the “MIPS Reference Data Card” from your textbook, also available within Course Materials in Submitty.

Modify the given helloworld.s code by changing the “Hello world” string to instead be “MIPS is awesome!” (and add a newline to the end of the output).

Take the time to understand how this example program works. Be sure you understand how to set up the system call (i.e., syscall). In particular, what happens if you load register $v0 with 1 instead of 4? In other words, describe what happens when you change the first main line to:

            main: li $v0, 1                                # syscall 4 (print_str)

What happens when you change the above value to 2? To 3? And so on?

Finally, also use this checkpoint to get familiar with the SPIM interface.

2.   Checkpoint 2: For the second checkpoint, you will translate the following block of high-level code into MIPS:

{

int x = 0;

if ( x < 5 )

{

x += 3;

}

}

To accomplish this, associate variable x with register $t0. In other words, register $t0 will hold the value of x. After you implement this logic in MIPS, use MIPS code to display result x using the following output format: x ($t0) equals <value-of-x

As an example, the above code example should output the following:

x ($t0) equals 3

You will need to make use of the print_string and print_int system calls, as well as the Set Less Than (slt) and Branch On Equal (beq) instructions.

Test your MIPS code by changing the initial value of $t0 to 2, 4, 5, 6, 100, etc.

3.   Checkpoint 3: For the third checkpoint, we will revisit the GCD algorithm, but this time implement it using MIPS. More specifically, in MIPS, implement the GCD algorithm that uses subtraction instead of the “mod” operator.

To complete this checkpoint, use registers $t0 and $t1 as inputs to your GCD code. You can hard-code these two values using Load Immediate (li) instructions. Make sure you use positive values less than 32768.

Finally, display the resulting GCD of the two given values. Use the format shown below:

GCD( <first-value, <second-value ) is <GCD-result

As an example, if values $t0 and $t1 are 45 and 54, respectively, the output is:

GCD( 45, 54 ) is 9

Try it again with inputs 54 and 45; in other words, make sure it works if you swap the two inputs!