MIPS Registers - Computation Structures Group

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Computer Architecture: A Constructive Approach
Introduction to SMIPS
Jihong Kim
Intro to SMIPS.1
Jihong Kim
Stored Program Concept
 Instructions are bits (i.e., as numbers)
 Programs are stored in memory
• to be read or written just like data
Treating Instructions in the
same way as Data
memory for data, programs,
compilers, editors, etc.
 Fetch & Execute Cycle
• Instructions are fetched and put into a special register
• Bits in the register "control" the subsequent actions
• Fetch the next instruction and continue
Intro to SMIPS.2
Jihong Kim
Multiple Levels of Representation
temp = v[k];
High Level Language
Program
v[k] = v[k+1];
v[k+1] = temp;
Compiler
lw
lw
sw
sw
Assembly Language
Program
Assembler
Machine Language
Program
0000
1010
1100
0101
1001
1111
0110
1000
1100
0101
1010
0000
$15,
$16,
$16,
$15,
0110
1000
1111
1001
1010
0000
0101
1100
0($2)
4($2)
0($2)
4($2)
1111
1001
1000
0110
0101
1100
0000
1010
1000
0110
1001
1111
Machine Interpretation
Control Signal
Specification
Intro to SMIPS.3
ALUOP[0:3] <= InstReg[9:11] & MASK
High and low signals on control lines
Jihong Kim
Instruction Set Architecture (subset of Computer Arch.)
“ ... the attributes of a [computing] system as seen by
the programmer, i.e. the conceptual structure and
functional behavior,
as distinct from the organization of the data flows and
controls, the logical design, and the physical
implementation. “
Amdahl, Blaaw, and Brooks, 1964
SOFTWARE
Intro to SMIPS.4
Jihong Kim
Example ISAs
 Intel 80x86
 ARM
 HP PA-RISC
 Sun Sparc
 SGI MIPS
 IBM/Motorola PowerPC
Intro to SMIPS.5
Jihong Kim
MIPS I Instruction Set Architecture
 Instruction Categories
•
•
•
Load/Store
Computational
Jump and Branch
•
Floating Point
- coprocessor
Memory Management
Special
•
•
Registers
r0 - r31
PC
HI
LO
3 Instruction Formats: all 32 bits wide
OP
rs
rt
OP
rs
rt
OP
rd
sa
funct
immediate
jump target
SMIPS: a subset of the full MIPS32 ISA
Intro to SMIPS.6
Jihong Kim
Execution Cycle
Instruction
(Conceptual Programmer’s View)
Obtain instruction from program storage
Fetch
Instruction
Determine required actions and instruction size
Decode
Operand
Locate and obtain operand data
Fetch
Execute
Compute result value or status
Result
Store
Deposit results in storage for later use
Next
Instruction
Intro to SMIPS.7
Determine successor instruction
Jihong Kim
MIPS Registers: Fast Locations for Data
 32 32-bit registers: $0, $1, … , $31
•
•
•
•
operands for integer arithmetic
address calculations
temporary locations
special-purpose functions defined by convention
 1 32-bit Program Counter (PC)
 2 32-bit registers HI & LO:
• used for multiply & divide
 32 32-bit registers: $f0, … $f31
• floating-point arithmetic (often used as 16 64-bit registers)
Intro to SMIPS.8
Jihong Kim
MIPS Load-Store Architecture
 Every operand must be in a register (a few
exceptions)
 Variables have to be loaded in registers.
 Results have to be stored in memory.
a=b+c
d=a+b
load b in register Rx
load c in register Ry
Rz = Rx + Ry
store Rz in a
Rt = Rz + Rx
store Rt in d
more variables than registers, so need explicit load and stores.
Intro to SMIPS.9
Jihong Kim
MIPS arithmetic
 All instructions have 3 operands
 Operand order is fixed (destination first)
Example:
Intro to SMIPS.10
C code:
MIPS code:
A=B+C
add $s0, $s1, $s2
C code:
A = B + C + D;
E = F - A;
MIPS code:
add $t0, $s1, $s2
add $s0, $t0, $s3
sub $s4, $s5, $s0
Jihong Kim
Registers vs. Memory
 Arithmetic instruction’s operands must be
registers:
only 32 registers provided
 Compiler associates variables with registers
 What about programs with lots of variables?
• Spilling registers
• For high performance, use registers efficiently!
Control
Input
Memory
Datapath
Processor
Intro to SMIPS.11
Output
I/O
Jihong Kim
Memory Organization
 Viewed as a large, single-dimension array, with an
address.
 A memory address is an index into the array
 "Byte addressing" means that the index points to a
byte of memory.
0
1
2
3
4
5
6
...
Intro to SMIPS.12
8 bits of data
8 bits of data
8 bits of data
8 bits of data
8 bits of data
Q: How to specify a memory location?
8 bits of data
8 bits of data
Jihong Kim
Load & Store Instructions
 Base+Offset addressing mode: offset(base register)
e.g., 32($s3)
 Example:
• C code: A[8] = h + A[8];
- A: an array of 100 words
-
the base address of the array A is in $s3
• MIPS code:
base register: $s3
offset: 32
lw $t0, 32($s3)
add $t0, $s2, $t0
sw $t0, 32($s3)
 Store word has destination last
Intro to SMIPS.13
Jihong Kim
Example: Compiling using a Variable Array Index
 C code:
g = h + A[i]
$s3: base register for A
g, h, i: $s1, $s2, $s4
 MIPS code:
add $t1, $s4, $s4
add $t1, $t1, $t1
Intro to SMIPS.14
# $t1 = 2 * i
# $t1 = 4 * i
add $t1, $t1, $s3
lw $t0, 0($t1)
# $t1 = address of A[i]
# $t0 = A[i]
add $s1, $s2, $t0
# g = h + A[i]
Jihong Kim
Control: bne & beq
 Decision making instructions
• alter the control flow,
• i.e., change the "next" instruction to be executed
 MIPS conditional branch instructions:
bne $t0, $t1, Label
beq $t0, $t1, Label
 Example:
if (i==j) h = i + j;
bne $s0, $s1, Label
add $s3, $s0, $s1
Label:
....
Intro to SMIPS.15
Jihong Kim
More Branch Instructions
 blez s, label
if (s <= 0) goto label
 bnez s, label
if (s != 0) goto label
Intro to SMIPS.16
Jihong Kim
Control: j
 MIPS unconditional branch instructions:
j label
 Example:
if (i!=j)
h=i+j;
else
h=i-j;
Intro to SMIPS.17
beq $s4, $s5, Lab1
add $s3, $s4, $s5
j Lab2
Lab1:sub $s3, $s4, $s5
Lab2:...
Jihong Kim
A Few More ASM Instructions
 sll d, s, shift
d = s << shift
 slt d, s, j
if (s < j) d = 1
else d = 0
 jr
r
Jump to the instruction pointed to by register r
Intro to SMIPS.18
Jihong Kim
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