CHAPTER 7 : INTRODUCTION TO MIPS AND QTSPIM SIMULATOR

THE ORGANIZATION OF A COMPUTER

-The 5 basic components of a computer are input , output , memory,datapath (old term called as ALU) and control with system bus that act as the communication channel for all other components . Figure 7-1 illustrates the organization of a computer .

1.      Datapath – is also called as ALU that perform arithmetic operations

2.      Control – the components of a processor that send the signals that determine the operation of the datapath ,memory ,input and output.

3.      Memory – the storage area where programs are kept when the program is running and contains data needed by the running program

4.      Input – devices that write data to memory

5.      Output – devices that read data from memory and convey result of the computation

MICROPROCESSOR OPERATIONS

-Every instruction starts by using the program counter to supply the instruction memory . After  the instruction is fetched , the register operands used by an instruction are specified by field of that instruction .Once the register operands have been fetched, the operation stated in machine instruction is performed .

Machine cycle :-

FETCH *Use the program counter (PC) to supply the instruction address *Fetch the instruction from memory *Update the PC

DECODE *Decode the instruction

EXECUTE *Read registers *Execute instruction *If necessary , write results to memory

INTRODUCTION TO MIPS R2000

*MIPS or Microprocessor without Interlocked Pipeline Stages is a reduced instruction set computer (RISC) instruction set architecture.

*The first commercial MIPS model,R2000 was announced in 1985.It had 32-bit general purpose registers , but no condition code register which the designers considered it a potential bottleneck.

MEMORY ALLOCATION

·        Text segment – this hold the machine language code for instruction in the source file (user program)

·        Data segment – this hold the data that the program operates on . It is devided into two parts . Static data contains data that are statically allocated whose size does not change as the program access them . On top of static data is dynamic data . This data is allocated and deallocated by the program execute .

·        Stack segment – this segment recides at the top of user address space . In a high level language program ,local variables and parameters are pushed and popped on the stack as the operating systems expands and shrink the stack segment toward the data segment.

MIPS REGISTER CONVENTIONS

REGISTER NAME (MNEMONIC NAME)	REGISTER NUMBER	USAGE
$zero	$0	Constant 0
$at	$1	Assembler temporary (reserved)
$v0-$v1	$2-$3	Expression evaluation and results of
$a0-$a3	$4-$7	Arguments to asubroutine
$t0-$t7	$8-$15	Temporary (not preserved across a function call)
$s0-4s7	$16-$23	Saved temporary (preserved across a function call)
$st8-$t9	$24-$25	More temporary
$gp	$28	Global pointer (preserved on call)
$sp	$29	Stack pointer(preserved on call)
$fp	$30	Frame pointer(preserved on call)
$ra	$31	Return address (automatically used in some instructions)

DATA REPRESENTATION

-In order to understand how to manipulate data and perform computation in MIPS

Program, you must understand how data is represented by a computer in a view of MIPS programming language.

ASCII representation of character

NUMBER REPRESENTATION

-Although computers operate on binary numbers,in MIPS number is represented in decimal system or hexadecimal system.When you need to insert number into a register , you have to remember what kind of number system that you want to write in the program.For example, to load number 16 into register $5 , we have two ways to represent decimal 16 in MIPS :

1.      Ori $5 , $0 , 16 #load number 16 into register $5

2.      Ori $5 , $0 , 0x10 #load number 16 into register $5

QtSPIM

-QtSPIM is a self-contained simulator that runs MIPS32 programs that emulates MIPS processor.MIPS processor has 32 general purpose registers , each holding 32 bits.The simulator runs on all Microsoft Windows,Mac OS x and Linux.

OPENING QtSPIM

1.      Register display – It list all 32 general purpose registers with the content where can choose to display in hex , binary , or decimal by right click the mouse on the register display . For beginner , choose Int Regs[16] to look the content of the register . Initially , the content of the registers is zero except for the stack pointer , which points to an empty stack.

2.      Data display – Contain user User Data Segment , User Stack and Kernel Data Segment.It shows the MIPS memory that hold data programmed by the user and usual data that has been pushed into the stack.

3.      Text Display – The first column is the addresses of the memory location of the machine instruction displayed in hexadecimal on the second column . Whereas,the third column is the assembly code to represent the machine instruction .

4.      SPIM Messages – It shows the messages from the simulator whether the assembly code has error(s) or not