The document discusses the MIPS instruction set architecture. It describes the MIPS ISA's registers and memory organization, with 32 general purpose registers and 4GB of maximum memory addressed through bytes or words. It outlines the main instruction formats - R-format for arithmetic/logical instructions, I-format for data transfer, and J-format for jumps. The key MIPS instruction types are described, including how they manipulate data in registers or move it between registers and memory.

1. Computer Architecture
06:- MIPS ISA

2. Outline - Instruction Sets
• Instruction Set Overview
• MIPS Instruction Set
• Overview
• Registers and Memory
• MIPS Instructions

3. MIPS
• MIPS:
Microprocessor without Interlocked Pipeline Stages
• We’ll be working with the MIPS instruction set architecture
• similar to other architectures developed since the 1980's
• Almost 100 million MIPS processors manufactured in 2002
• used by NEC, Nintendo, Cisco, Silicon Graphics, Sony, …

4. Outline - Instruction Sets
• Instruction Set Overview
• MIPS Instruction Set
• Overview
• Registers and Memory
• MIPS Instructions

5. MIPS Registers and Memory
Memory
4GB Max
(Typically 64MB-1GB)
0x00000000
0x00000004
0x00000008
0x0000000C
0x00000010
0x00000014
0x00000018
0x0000001C
0xfffffff4
0xfffffffc
0xfffffffc
PC = 0x0000001C
Registers
32 General Purpose Registers
R0
R1
R2
R30
R31
32 bits

6. MIPS Registers and Usage
Name Register number Usage
$ z e r o 0 the constant value 0
$ a t 1 reserved for assembler
$ v 0 - $ v 1 2-3 values for results and expression evaluation
$ a 0 - $ a 3 4-7 arguments
$ t 0 - $ t 7 8-15 temporary registers
$ s 0 - $ s 7 16-23 saved registers
$ t 8 - $ t 9 24-25 more temporary registers
$ k 0 - $ k 1 26-27 reserved for Operating System kernel
$ g p 28 global pointer
$ s p 29 stack pointer
$ f p 30 frame pointer
$ r a 31 return address
Each register can be referred to by number or name.

7. More about MIPS Memory Organization
• Two views of memory:
• 232 bytes with addresses 0, 1, 2, …, 232-1
• 230 4-byte words* with addresses 0, 4, 8, …, 232-4
• Both views use byte addresses
• Word address must be multiple of 4 (aligned)
8 bits
0x00000000
0x00000001
0x00000002
0x00000003
0x00000000
0x00000004
0x00000008
0x0000000C
32 bits
0 1 2 3
*Word sizes vary in
other architectures

8. MIPS Instructions
• All instructions exactly 32 bits wide
• Different formats for different purposes
• Similarities in formats ease implementation
op rs rt offset
6 bits 5 bits 5 bits 16 bits
op rs rt rd functshamt
6 bits 5 bits 5 bits 5 bits 5 bits 6 bits
R-Format
I-Format
op address
6 bits 26 bits
J-Format
31 0
31 0
31 0

9. MIPS Instruction Types
• Arithmetic & Logical - manipulate data in registers
add $s1, $s2, $s3 $s1 = $s2 + $s3
or $s3, $s4, $s5 $s3 = $s4 OR $s5
• Data Transfer - move register data to/from memory
lw $s1, 100($s2) $s1 = Memory[$s2 + 100]
sw $s1, 100($s2) Memory[$s2 + 100] = $s1
• Branch - alter program flow
beq $s1, $s2, 25 if ($s1==$s1) PC = PC + 4 + 4*25

10. MIPS Arithmetic & Logical Instructions
• Instruction usage (assembly)
add dest, src1, src2 dest=src1 + src2
sub dest, src1, src2 dest=src1 - src2
and dest, src1, src2 dest=src1 AND src2
• Instruction characteristics
• Always 3 operands: destination + 2 sources
• Operand order is fixed
• Operands are always general purpose registers
• Design Principles:
• Design Principle 1: Simplicity favors regularity
• Design Principle 2: Smaller is faster

11. Arithmetic & Logical Instructions - Binary
Representation
• Used for arithmetic, logical, shift instructions
• op: Basic operation of the instruction (opcode)
• rs: first register source operand
• rt: second register source operand
• rd: register destination operand
• shamt: shift amount (more about this later)
• funct: function - specific type of operation
• Also called “R-Format” or “R-Type” Instructions
op rs rt rd functshamt
6 bits 5 bits 5 bits 5 bits 5 bits 6 bits
031

12. op rs rt rd functshamt
6 bits 5 bits 5 bits 5 bits 5 bits 6 bits
Decimal
Binary
Arithmetic & Logical Instructions -
Binary Representation Example
• Machine language for
add $8, $17, $18
• See reference card for op, funct values
000000
0
10001
17
10010
18
01000
8
00000
0
100000
32
031

13. MIPS Data Transfer Instructions
• Transfer data between registers and memory
• Instruction format (assembly)
lw $dest, offset($addr) load word
sw $src, offset($addr)store word
• Uses:
• Accessing a variable in main memory
• Accessing an array element

14. Example - Loading a Simple Variable
lw R5,8(R2) Memory
0x00
Variable Z = 692310
Variable X
Variable Y
0x04
0x08
0x0c
0x10
0x14
0x18
0x1c
8
+
Registers
R0=0 (constant)
R1
R2=0x10
R30
R31
R3
R4
R5R5
R2=0x10
R5 = 629310
Variable Z = 692310

15. Data Transfer Example - Array Variable
Registers
R0=0 (constant)
R1
R2=0x08
R30
R31
R3
R4
R5=105
C Program: int a[5];
a[3] = z;
Assembly: sw $5,12($2)
12=0xc
+
Memory
0x00
a[0]
a[4]
a[2]
a[1]
a[3]
0x04
0x08
0x0c
0x10
0x14
0x18
0x1c
Base Address
R5=105
R2=0x08
a[3]=105
scaled offset

16. Data Transfer Instructions -
Binary Representation
• Used for load, store instructions
• op: Basic operation of the instruction (opcode)
• rs: first register source operand
• rt: second register source operand
• offset: 16-bit signed address offset (-32,768 to
+32,767)
• Also called “I-Format” or “I-Type” instructions
op rs rt offset
6 bits 5 bits 5 bits 16 bits
Address

17. I-Format vs. R-Format Instructions
• Compare with R-Format
offset
6 bits 5 bits 5 bits 16 bits
I-Formatop rs rt
rd functshamt
6 bits 5 bits 5 bits 5 bits 5 bits 6 bits
R-Formatop rs rt
Note similarity!

18. I-Format Example
• Machine language for
lw $9, 1200($8) == lw $t1, 1200($t0)
op rs rt offset
6 bits 5 bits 5 bits 16 bits
Binary
Decimal35 8 9 1200
100011 01000 01001 0000010010110000
031

19. Binary Representation - Jump
• Jump Instruction uses J-Format (op=2)
• What happens during execution?
PC = PC[31:28] : (IR[25:0] << 2)
op address
6 bits 26 bits
Conversion to
word offset
Concatenate
upper 4 bits
of PC to form
complete
32-bit address

20. How to Decode?
• What is the assembly language statement
corresponding to this machine instruction?
0x00af8020
• Convert to binary
0000 0000 1010 1111 1000 0000 0010 0000
• Decode
• op: 00000
• rs: 00101
• rt: 01111
• rd: 10000
• shamt: 00000
• funct: 100000
• Solution: add $s0, $a1, $t7

21. Summary - MIPS Instruction Set
• simple instructions all 32 bits wide
• very structured, no unnecessary baggage
• only three instruction formats
op rs rt offset
6 bits 5 bits 5 bits 16 bits
op rs rt rd functshamt
6 bits 5 bits 5 bits 5 bits 5 bits 6 bits
R-Format
I-Format
op address
6 bits 26 bits
J-Format

22. Coming up Next
MIPS Assembly Language.
C u ……. Take Care,,,