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1 .Design of the MIPS Processor We will study the design of a simple version of MIPS that can support the following instructions: • I-type instructions LW, SW • R-type instructions, like ADD, SUB • Conditional branch instruction BEQ • J-type branch instruction J The instruction formats 6-bit 5-bit 5-bit 5-bit 5-bit 5-bit LW op rs rt immediate SW op rs rt immediate ADD op rs rt rd 0 func SUB op rs rt rd 0 func BEQ op rs rt immediate J op address
2 .ALU control ALU control (3-bit) 32 ALU result 32 ALU control input ALU function 000 AND 001 OR 010 add 110 sub 111 Set less than How to generate the ALU control input? The control unit first generates this from the opcode of the instruction.
3 .A single-cycle MIPS We consider a simple version of MIPS that uses Harvard architecture. Harvard architecture uses separate memory for instruction and data. Instruction memory is read-only – a programmer cannot write into the instruction memory. To read from the data memory, set Memory read =1 To write into the data memory, set Memory write =1
4 .Instruction fetching Clock Each clock cycle fetches the instruction from the address specified by the PC, and increments PC by 4 at the same time.
5 .Executing R-type instructions This is the instruction format for the R-type instructions.
6 .Here are the steps in the execution of an R-type instruction: ! Read instruction ! Read source registers rs and rt ! ALU performs the desired operation ! Store result in the destination register rd. Q. Why should all these be completed in a single cycle?
7 .Executing lw, sw instructions These are I-type instructions. op rs rt address Try to recognize the steps in the execution of lw and sw.