Question

(a) Consider the following MIPS memory with data shown in hex, which are located in memory from address 0 through 15. Show the result of the MIPS instruction “lw $s0, 4($a0)” for machines in little-endian byte orders, where $a0 = 4.  

Address	Contents
0	8a
1	9b
2	a3
3	b4
4	c5
5	6d
6	7e
7	8f

Address	Contents
8	0a
9	1b
10	2c
11	3d
12	4e
13	5f
14	66
15	70

(b) )Assume we have the following time, performance and architecture parameters in the specified units.

Ec = execution time in cycles/program

Es = execution time in seconds/program

Pr = performance rate in instructions/seconds

CCT = clock cycle time in second/cycle

CR = clock rate in cycle/second

IC = instructions in instructions/program

CPI = average cycles per instruction in cycle/instruction

Complete the following formulas with the appropriate parameter

      CR = 1/____,                ____ = IC´ CPI,             Es =  ____ ´ CPI ´ CCT

Answer 1

(a)

lw $s0, 4($a0)

This instruction loads a word into register $s0, from the effective address

= 4 + $a0

= 4 + 4

= 8

Now, since the system is little-endian, so the Least Significant Byte (LSB) will be stored at lower address, and Most Significant Byte (MSB) will be stored at higher address.

So, we need to fetch 4 bytes beginning from address 8, abut reverse them to give the logical value in destination register $s0.

Thus,

$s0 <- 0x3d2c1b0a

(b)

1.

CR = 1 / CCT

Reasoning notes :

• CR = Number of cycles per second
• CCT = Clock cycle time, so number of cycles per second is simply its inverse

2.

Ec = IC * CPI

Reasoning notes :

• CPI is the number of cycles required per instruction, and IC is the total number of instructions in the program. So, multiplying them gives the total number of cycles in the program.

3.

Es = IC * CPI * CCT

Reasoning notes :

• CPI is the number of cycles required per instruction, and CCT is the clock cycle time (in seconds). So, multiplying them gives the time per instruction (in seconds).
• Multiplying the above quantity further with IC, gives the time for the program (in seconds).