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CSE-306-Computer-Architecture-Sessional

This is a repository containing all the simulations and reports of CSE-306 Computer Architecture Sessional.

4 bit ALU

This ALU contains:

  • Two 4 bit inputs A and B
  • Three select bits S2, S1, S0 as ALU opcodes
  • One 4 bit output
  • Four flags: Z (Zero), C (Carry), O (Overflow), N (Negative)

Implemented functions and opcodes:

ALU opcodes Functions
S2 S1 S0 (Cin)
0 0 0 Transfer A
0 0 1 Increment A
0 1 X AND
1 0 0 Add
1 0 1 Add with carry
1 1 X OR

Truth table:

ALU opcodes Required outputs Adder inputs Functions
S2 S1 S0 (Cin) Xi Yi Zi
0 0 0 A Ai 0 Ci Transfer A
0 0 1 A + 1 Increment A
0 1 0 A ^ B AiBi 0 0 AND
0 1 1
1 0 0 A + B Ai Bi Ci Add
1 0 1 A + B + 1 Add with carry
1 1 0 A OR B AiBi' Bi 0 OR
1 1 1

Simplified inputs to individual full adders:

Xi = A(S1' + S2 XOR B)

Yi = S2B

Zi = S1'Ci

Circuit diagram:

4 bit ALU circuit diagram

Floating Point Adder

The adder takes two 32 bit floating point numbers and adds them together. The numbers are represented in the following format:

Sign Exponent Fraction
1 bit 10 bits 21 bits (Lowest bits)

The numbers are in normalized form. There are two flags U (underflow) and O (overflow) which are set if the result is too small or too large to be represented in the format.

Flow chart:

Circuit diagram:

Floating point adder circuit diagram

What individual components do:

  • Sign check: Checks if a 32 floating point number is positive, negative or the exponent is zero. If the number is positive then the output is the same as input. If the number is negative then it outputs the two's complement of the input. And if the exponent is zero then the output is zero.
  • Normalizer: Normalizes a floating point number. But if the number is overflowed or underflowed while trying to normalize then the appropriate flags are set.
  • Rounder: Rounds the 32 bit significand to 21 bits.

4 bit MIPS processor

How to use:

Write a valid MIPS assembly code and compile the code with MIPS-assembler. Now open the MIPS-simulator with logisim 2.7.1 Then open the machine.txt file (generated after runnig the C++ code) from the instruction memory.

MIPS instruction formats:

  • R-type:

Opcode Src Reg 1 Src Reg 2 Dst Reg
4-bits 4-bits 4-bits 4-bits

  • S-type:

Opcode Src Reg 1 Dst Reg Shamt
4-bits 4-bits 4-bits 4-bits

  • I-type:

Opcode Src Reg 1 Src Reg 2/Dst Reg Addr./Immdt
4-bits 4-bits 4-bits 4-bits

  • J-type:

Opcode Target Jump Address 0
4-bits 8-bits 4-bits

Instruction set:

Instruction Opcode Instruction MIPS Instruction Format Instruction Type
0000 sub R Arithmetic
0001 ori I Logic
0010 bneq I Control
0011 addi I Arithmetic
0100 beq I Control
0101 or R Logic
0110 sw I Memory
0111 srl S Logic
1000 and R Logic
1001 andi I Logic
1010 lw I Memory
1011 add R Arithmetic
1100 sll S Logic
1101 subi I Arithmetic
1110 j J Control
1111 nor R Logic

Circuit diagram:

4-bit MIPS Circuit Diagram

Group members: