< Computer Architecture Lab < SS2013

ISA

32-bit architecture, based on MIPS

Registers

  • 32 x 32-bit GPR name R0-R31, R0 always contains ‘0’, even if other value is stored in it.
  • PC – Program Counter, inaccessible directly from assembler
  • IF/ID, ID/EX, EX/MEM, MEM/WB – for pipeline, inaccessible from assembler (IF - instruction fetch, ID - instruction decode, EX - execute, MEM - memory access, WB - write back)
  • AOL, AOH - registers that store 64-bit result of ALU operation (for 64-bit operands and 32- bit operands multiplication/division). AOL (states for Alu-Out-Low) contains lower 32 bits of result, AOH (Alu - Out - High) - higher 32 bits. (equivalent of LO and HI in MIPS!)

General structure of instructions

ALU

32-bit (ALU operands)
Rd = Rs (fuction) Rt

Opcode (6)

Rs (5)

Rt (5)

Rd (5)

shift (5)

Function (6)

64-bit (ALU operands)
AOH AOL = (([Rs+1]<<32)+Rs) (function) (([Rt+1]<<32)+Rt)

Or, more formally:

AOL = ((([Rs+1]<<32)+Rs) (function) (([Rt+1]<<32)+Rt)) AND (232 -1)
AOH = ((([Rs+1]<<32)+Rs) (function) (([Rt+1]<<32)+Rt)) >> 32

Note: (Rs or Rt = 31 will be coupled with R0! It gives us simple way to add 64- and 32-bit numbers by putting 32-bit one in R31)
(It is some kind of Little Endian that simplifies implementation)

Opcode(6)

Rs (5)

Rt (5)

Shift (10)

Function(6)

Immediate
Rd = Rs (function) Value

Opcode (6)

Rs (5)

Rd (5)

Value (16)


MEMORY

Opcode (6)

Rs (5)

Rd (5)

Offset (16)


CONTROL

Jump

Opcode (6)

Address (26)


Jump to address stored in register

Opcode (6)

Rs (5)

Empty(21)

Branch

Opcode (6)

Rs (5)

Rt (5)

Value (16)

Value is signed

SPECIAL REGISTERS

Opcode (6)

Empty(5)

Rd(5)

Empty(16)

Instruction Set

Category
Name
Syntax
Meaning
Encoding
ALU, 32-bit, Arithmetic

Add

add Rs,Rt,Rd

Rd = Rs + Rt

000001ssssstttttddddd-----000000

Add Unsigned

addu Rs,Rt,Rd

Rd = Rs + Rt

000001ssssstttttddddd-----000001

Subtract

sub Rs,Rt,Rd

Rd = Rs - Rt

000001ssssstttttddddd-----000010

Subtract Unsigned

subu Rs,Rt,Rd

Rd = Rs - Rt

000001ssssstttttddddd-----000011

Multiply

mul Rs,Rt,Rd

Rd = Rs * Rt

000001ssssstttttddddd-----000100

Multiply Unsigned

mulu Rs,Rt,Rd

Rd = Rs * Rt

000001ssssstttttddddd-----000101

Divide

div Rs,Rt,Rd

Rd = Rs / Rt

000001ssssstttttddddd-----000110

Divide Unsigned

divu Rs,Rt,Rd

Rd = Rs / Rt

000001ssssstttttddddd-----000111

Add Immediate

addi Rs,Rd,C

Rd = Rs + C

000011sssssdddddcccccccccccccccc

Add Immediate

Unsigned

addiu Rs,Rd,C

Rd = Rs + C

000101sssssdddddcccccccccccccccc

Multiply to Long

mull Rs,Rt

AOL = ((Rs * Rt) << 32) >> 32

AOH = (Rs * Rt) >> 32

000001sssssttttt----------010000

Multiply to Long Unsigned

mullu Rs,Rt

AOL = ((Rs * Rt) << 32) >> 32

AOH = (Rs * Rt) >> 32

000001sssssttttt----------010001

Divide to Long

divl Rs,Rt

AOL = Rs / Rt

AOH = Rs % Rt

000001sssssttttt----------010010

Divide to Long Unsigned

divlu Rs,Rt

AOL = Rs / Rt

AOH = Rs % Rt

000001sssssttttt----------010011

ALU, 32-bit, Logic

And

and Rs,Rt,Rd

Rd = Rs & Rt

000001ssssstttttddddd-----001000

And Immediate

andi Rs,Rd,C

Rd = Rs & C

000111sssssdddddcccccccccccccccc

Or

or Rs,Rt,Rd

Rd = Rs | Rt

000001ssssstttttddddd-----001001

Or Immediate

ori Rs,Rd,C

Rd = Rs | C

001001sssssdddddcccccccccccccccc

Nand

nand Rs,Rt,Rd

Rd = ~( Rs & Rt )

000001ssssstttttddddd-----001010

Nand Immediate

nandi Rs,Rd,C

Rd = ~( Rs & C )

001011sssssdddddcccccccccccccccc

Nor

nor Rs,Rt,Rd

Rd = ~( Rs & Rt )

000001ssssstttttddddd-----001011

Nor Immediate

nori Rs,Rd,C

Rd = ~( Rs & C )

001101sssssdddddcccccccccccccccc

Xor

xor Rs,Rt,Rd

Rd = Rs ^ Rt

000001ssssstttttddddd-----001100

Xor Immediate

xori Rs,Rd,C

Rd = Rs ^ C

001111sssssdddddcccccccccccccccc

Xnor

Xnor Rs,Rd,C

Rd = ~( Rs ^ Rt )

000001ssssstttttddddd-----001101

Xnor Immediate

Xnori Rs, Rt,Rd

Rd = ~( Rs ^ C )

010001sssssdddddcccccccccccccccc

ALU, 32-bit, Bitwise Shift

Shift left logical

sll Rs, Rd, shift

Rd = Rs << shift

000001sssssddddd-----shift011000

Shift right logical

srl Rs, Rd, shift

Rd = Rs >> shift

000001sssssddddd-----shift011001

Shift right arithmetic

sra Rs, Rd, shift

Rd = Rs >> shift (arithmetic – difficult formula)

000001sssssddddd-----shift011010

ALU, 64-bit, Arithmetic

Add

ladd Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)+ (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)+ (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------000000

Add Unsigned

laddu Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)+ (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)+ (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------000001

Subtract

lsub Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)- (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)-(((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------000010

Subtract Unsigned

lsubu Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)- (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)- (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------000011

Multiply

lmul Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)* (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)* (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------000100

Multiply Unsigned

lmulu Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)* (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)* (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------000101

Divide

ldiv Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)/ (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)/ (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------000110

Divide Unsigned

ldivu Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)/ (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)/ (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------000111

ALU, 64-bit, Logic

And

land Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)& (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)& (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------001000

Or

lor Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)| (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)| (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------001001

Nand

lnand Rs,Rt

AOL =~(((((Rs+1)<<32)+Rs)& (((Rt+1)<<32)+Rt))) AND (232 -1)

AOH =~(((((Rs+1)<<32)+Rs)& (((Rt+1)<<32)+Rt))) >>32

000010sssssttttt----------001010

Nor

lnor Rs,Rt

AOL =~(((((Rs+1)<<32)+Rs)| (((Rt+1)<<32)+Rt))) AND (232 -1)

AOH =~(((((Rs+1)<<32)+Rs)|(((Rt+1)<<32)+Rt))) >>32

000010sssssttttt----------001011

Xor

lxor Rs,Rt

AOL = ((((Rs+1)<<32)+Rs)^ (((Rt+1)<<32)+Rt)) AND (232 -1)

AOH =((((Rs+1)<<32)+Rs)^ (((Rt+1)<<32)+Rt)) >>32

000010sssssttttt----------001100

Xnor

lxnor Rs,Rt

AOL =~(((((Rs+1)<<32)+Rs)^ (((Rt+1)<<32)+Rt))) AND (232 -1)

AOH =~(((((Rs+1)<<32)+Rs)^ (((Rt+1)<<32)+Rt))) >>32

000010sssssttttt----------001101

ALU, 64-bit, Bitwise Shift

Shift left logical

lsll Rs, shift

AOL = ((((Rs+1)<<32)+Rs) << shift) AND (232 -1)

AOH= ((((Rs+1)<<32)+Rs) << shift) >> 32

000010sssss-----shiftshift011000

Shift right logical

lsrl Rs, shift

AOL = ((((Rs+1)<<32)+Rs) >> shift) AND (232 -1)

AOH= ((((Rs+1)<<32)+Rs) >> shift) >> 32

000010sssss-----shiftshift011001

Shift right arithmetic

lsra Rs, shift

AOL = ((((Rs+1)<<32)+Rs) >> shift) AND (232 -1)

AOH= ((((Rs+1)<<32)+Rs) >> shift) >> 32

(arithmetic shift!! – difficult formula)

000010sssss-----shiftshift011010

MEMORY

Load word

lw Rd,Rs(C)

Rd = MEMORY[Rs + C]

000100sssssdddddcccccccccccccccc

Load half

lh Rd,Rs(C)

Rd = MEMORY[Rs + C] (signed)

000110sssssdddddcccccccccccccccc

Load half unsigned

lhu Rd,Rs(C)

Rd = MEMORY[Rs + C] (unsigned - without sign ext.)

001000sssssdddddcccccccccccccccc

Load byte

lb Rd,Rs(C)

Rd = MEMORY[Rs + C] (signed)

001010sssssdddddcccccccccccccccc

Load byte unsigned

lbu Rd,Rs(C)

Rd = MEMORY[Rs + C] (unsigned - without sign ext.))

001100sssssdddddcccccccccccccccc

Store word

sw Rd,Rs(C)

MEMORY[Rs + C] = Rd

001110sssssdddddcccccccccccccccc

Store half

sh Rd,Rs(C)

MEMORY[Rs + C] = Rd

010000sssssdddddcccccccccccccccc

Store byte

sb Rd,Rs(C)

MEMORY[Rs + C] = Rd

010010sssssdddddcccccccccccccccc

SPECIAL REGISTERS

Move From AOL

maol Rd

Rd = AOL

010100-----ddddd--------------------

Move From AOH

maoh Rd

Rd = AOH

010110-----ddddd--------------------

CONTROL 32-bit

Jump

j A

PC = (PC+4)[31:28] . A*4

010011aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

Jump register

jr Rs

PC = Rs

010101sssss-------------------------

Branch if equal

beq Rs,Rt,C

If (Rs == Rt) PC = PC+4+4*C

010111ssssstttttcccccccccccccccc

Branch if not equal

bne Rs,Rt,C

If (Rs != Rt) PC = PC+4+4*C

011001ssssstttttcccccccccccccccc

Branch if greater than

bgt Rs,Rt,C

If (Rs > Rt) PC = PC+4+4*C

011011ssssstttttcccccccccccccccc

Unsigned branch if greater than

bgtu Rs,Rt,C

If (Rs > Rt) PC = PC+4+4*C

011101ssssstttttcccccccccccccccc

Branch if greater or equal to

bge Rs,Rt,C

If (Rs >= Rt) PC = PC+4+4*C

011111ssssstttttcccccccccccccccc

Unsigned branch if greater or equal to

bgeu Rs,Rt,C

If (Rs >= Rt) PC = PC+4+4*C

100001ssssstttttcccccccccccccccc

Branch if less than

blt Rs,Rt,C

If (Rs < Rt) PC = PC+4+4*C

100011ssssstttttcccccccccccccccc

Unsigned branch if less than

bltu Rs,Rt,C

If (Rs < Rt) PC = PC+4+4*C

100101ssssstttttcccccccccccccccc

Branch if less or equal to

ble Rs,Rt,C

If (Rs <= Rt) PC = PC+4+4*C

100111ssssstttttcccccccccccccccc

Unsigned branch if less or equal to

bleu Rs,Rt,C

If (Rs <= Rt) PC = PC+4+4*C

101001ssssstttttcccccccccccccccc

CONTROL 64-bit

Branch if equal

lbeq Rs,Rt,C

If (((Rs+1)<<32+Rs) ==((Rt+1)<<32+Rt)) PC = PC+4+4*C

101000ssssstttttcccccccccccccccc

Branch if not equal

lbne Rs,Rt,C

If (((Rs+1)<<32+Rs) !=((Rt+1)<<32+Rt)) PC = PC+4+4*C

101010ssssstttttcccccccccccccccc

Branch if greater than

lbgt Rs,Rt,C

If (((Rs+1)<<32+Rs) >((Rt+1)<<32+Rt)) PC = PC+4+4*C

101100ssssstttttcccccccccccccccc

Unsigned branch if greater than

lbgtu Rs,Rt,C

If (((Rs+1)<<32+Rs) >((Rt+1)<<32+Rt)) PC = PC+4+4*C

101110ssssstttttcccccccccccccccc

Branch if greater or equal to

lbge Rs,Rt,C

If (((Rs+1)<<32+Rs) >=((Rt+1)<<32+Rt)) PC = PC+4+4*C

110000ssssstttttcccccccccccccccc

Unsigned branch if greater or equal to

lbgeu Rs,Rt,C

If (((Rs+1)<<32+Rs) >=((Rt+1)<<32+Rt)) PC = PC+4+4*C

110010ssssstttttcccccccccccccccc

Branch if less than

lblt Rs,Rt,C

If (((Rs+1)<<32+Rs) <((Rt+1)<<32+Rt)) PC = PC+4+4*C

110100ssssstttttcccccccccccccccc

Unsigned branch if less than

lbltu Rs,Rt,C

If (((Rs+1)<<32+Rs) <((Rt+1)<<32+Rt)) PC = PC+4+4*C

110110ssssstttttcccccccccccccccc

Branch if less or equal to

lble Rs,Rt,C

If (((Rs+1)<<32+Rs) <=((Rt+1)<<32+Rt)) PC = PC+4+4*C

111000ssssstttttcccccccccccccccc

Unsigned branch if less or equal to

lbleu Rs,Rt,C

If (((Rs+1)<<32+Rs) <=((Rt+1)<<32+Rt)) PC = PC+4+4*C

111010ssssstttttcccccccccccccccc

Note 1: Constant in all branches is signed!

Note 2: In MIPS only branches ‘equal’ and ‘not equal’ are implemented, but we can implement other using multiple ALU flags to determine if statement is true or not (e.g. A is greater than B if A-B results in flags Negative and Zero both equal to 0).

Changes

List of changes in comparison with word doc (too much to put in the summary):

  • 64-bit ALU operations use only 2 registers instead of 4 (Rs+1 and Rt+1 replace Ru and Rv)
  • 64-bit CONTROL instructions were added (thanks previous change).

There is some free opcodes that can be used to implement functions like 'multiply immediate' or '64-bit something immediate', but they are not neccesery and I would prefer to have some free opcodes ;).

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