0706.205.01 Computer Organization

Due Date

Friday, April 19 (11:59pm)

Form of Submission

Homework must be submitted via email.

Preparation

Patterson & Hennessy. Section 4.1-4.5; Appendix Section A.9

Question

1. Consider the truth table for a 1-bit adder on Slide 13 of the April 10 lecture. In the manner of the CarryOut formula (Slide 14), produce a logical formula (composed of ANDs and ORs) for the 1-but Sum.

2. Below is the subprogram from the midterm, adapted to run inside spim, the MIPS simulator. Save it to a file on Elvis, and run it inside the simulator.
   1. Change the program so that instead of turning its input (the contents of memory addressed by register $a0) into all upper-case, it turns it into all lower-case.
   2. Email me the modified program.

           .data
   str:
           .asciiz "Hello"
   orig:
           .asciiz "\nThe input: "
   now:
           .asciiz "\nThe output: "
   v0:
           .asciiz "\n  $v0 = "
   end:
           .asciiz "\n\n"
           .text
   START:  
           add     $v0, $zero, $zero       
   
   LOOP:   lb      $t0, 0($a0)
           beq     $t0, $zero, DONE
   
           addi    $sp, $sp, -12           # allocate space on stack
           sw      $a0, 0($sp)
           sw      $ra, 4($sp)
           sw      $v0, 8($sp)
   
           add     $a0, $t0, $zero
           jal     DOIT
   
           lw      $a0, 0($sp)
           lw      $ra, 4($sp)
   
           sb      $v0, 0($a0)
           lw      $v0, 8($sp)
           addi    $a0, $a0, 1
           addi    $v0, $v0, 1
           addi    $sp, $sp, 12
           j       LOOP
   
   DONE:   jr      $ra
   
   
   DOIT:   add     $v0, $a0, $zero
           slti    $t2, $v0, 97
           bne     $t2, $zero, SKIP
           slti    $t2, $v0, 123
           beq     $t2, $zero, SKIP
           addi    $v0, $v0, -32
   
   SKIP:   jr      $ra
   
   
   
   __start:
           addi    $v0, $zero, 4
           la      $a0, orig
           syscall
   
           li      $v0, 4
           la      $a0, str
           syscall
   
           la      $a0, str
           jal     START
   	move	$t0, $v0	# save return value 
   
           li      $v0, 4
           la      $a0, now
           syscall
   
           li      $v0, 4
           la      $a0, str
           syscall
   
           li      $v0, 4
           la      $a0, v0
           syscall
   	
           li      $v0, 1
           move    $a0, $t0
           syscall
   	
           li      $v0, 4
           la      $a0, end
           syscall