[Computer Architecture] The Processor

Load a instruction from memory (fetch)

User the opcode field to identify the instruction type(decode_

Arithmetic/logic : add, sub, and, or

• read 2 operand values from register
• perform calculation
• write the result back into register
• add 4 to pcMemory access : lw
• read 1 word from the register (base address)
• add the base address with the offset(Immediate field)
• load word from data memory (Address : base address + offset)
• write loaded word into the register
• add 4 to PCMemory access : sw
• read 1 word from the register file (base address)
• add the base address with the offset (imm field)
• read 1 word from the regiser : value to store
• store the word to data memory (address : base address + offset)
• add 4 to PCControl transfer : beq
• read 2 words from the register
• perfom comparison (using ALU): substraction
• if *rs1 == *rs2 -> pc < pc+imm
  else pc <-pc +4

Instruction/ Data Memroy

CPU
instruction cache data cache
main memory

R-Format instructions

Read: Behaves like combinational logic
Read Register 1/2 : register IDs from the current instruction
Read Date 1/2 : The current value of the corresponding registers

Write : behaves like a sequential logic
if RegWrite is "1", writes the values to the target register
write happends when moving to the next cycle

Arithmetic Logic Unit(ALU)

ALU operation (4-bit input) selects actual function

load/store : add
branch : subtract
r-type : fun7, fun3 fields

 

ALU control bits

 

 

 

Data Memory

MemRead : gives the current memory value from the address

MemWrite: writes the data to the address

 

Branch Condition test