Question

1. Consider the following MIPS instruction:

1. Loop:    add $t1, $s1, $s2

2.          or $s2, $s5, $s6

3.          bne $s2, $t8, Loop

4.          nop

Re-write the third instruction (bne) in binary.

Answer 1

Consider the following MIPS instruction:

Loop: add $t1, $s1, $s2

or $s2, $s5, $s6

bne $s2, $t8, Loop

nop

Re-writing Bne instruction in Binary:

Let's assume that Loop subroutine start at address 0x1000. So, writing instruction with addresses:

Loop: add St1, Ss1, Ss2 1000: 1004 1008: 100C: or Ss2, Ss5, Ss6 bne Ss2, St8, Loop nop

Instruction Format:

BNE - Branch on Not Equal

bne rs, rt, offset [I-type instruction]

Branch to specified offset if (rs != rt)

Given bne $s2, $t8, Loop: Branch to Loop if ($s2 != $t8)

Converting Given instruction bne to Binary:

31 26 25 21 20 16 15 Ss2 10010 St8 11000 Offset: Loop BNE 000101 6 bits 0001000000000000 5 bits 5bits 16 bits

Machine code for each field:

BNE: 000101 (6 bits)

$s2: 10010 (5 bits) ($s2 = $18 decimal value)

$t8: 11000 (5 bits) ($t8 = $24 decimal value)

Loop: 0001000000000000 (16 bits) (We have assume that Loop is at address 0x1000)

Binary of BNE instruction: bne $s2, $t8, Loop

Binary: 00010110010110000001000000000000

Hex: 0x16581000