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Pipelining: Implementation

Explore the workings of a MIPS instruction in a five-stage pipeline - from fetching to write-back. Learn the intricacies and benefits of pipelining in MIPS architecture.

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Pipelining: Implementation

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  1. 06 Pipelining:Implementation Kai Bu kaibu@zju.edu.cn http://list.zju.edu.cn/kaibu/comparch2017

  2. MIPS Five-Stage Data PathUnderneath Pipelining IF ID EX MEM WB Pipeline Register Store temporary result from the previous stage; Feed it to the next stage

  3. Data PathUnderneath Pipelining IF ID EX MEM WB

  4. Data PathUnderneath Pipelining lab & exam

  5. Preview under MIPS architecture • How a MIPS instruction works? • How MIPS instructions pipleline?

  6. How an un-pipelined MIPS instruction works?

  7. MIPS Instruction • at most 5 clock cycles per instruction • IF ID EX MEM WB

  8. IF IF ID EX MEM WB • Instruction Fetch cycle IR ← Mem[PC]; NPC ← PC + 4; IR: instruction register NPC: next sequential PC (32-bit instruction)

  9. ID IF ID EX MEM WB • Instruction Decode/register fetch A ← Regs[rs]; B ← Regs[rt]; Imm ← sign-extended immediate field of IR (lower 16 bits of Imm)

  10. EX IFID EX MEM WB • Execution/effective address cycle ALU operates on the operands from ID: 4 functions depending on the instr type -Memory reference -Register-register ALU instruction -Register-immediate ALU instruction -Branch

  11. EX IFID EX MEM WB • Execution/effective address cycle -Memory reference ALUOutput ← A + Imm; ALU adds the operands to form effective address

  12. EX IFID EX MEM WB • Execution/effective address cycle -Register-register ALU instr ALUOutput ← A func B; ALU performs the operation specified by function code on the values in register A & register B

  13. EX IFID EX MEM WB • Execution/effective address cycle -Register-Immediate ALU Instr ALUOutput ← A op Imm; ALU performs the operation specified by opcode on the values in register A & reg IMM

  14. function code vs opcode?

  15. function code vs opcode? 1stsrc 2ndsrcdst shift w/ opcode to select instr reg-reg 1stsrcsrc for branch 16-bit address reg-imm dst for I-type why sign-extended

  16. EX IFID EX MEM WB • Execution/effective address cycle -Branch ALUOutput ← NPC + (Imm<<2); Cond ← (A == 0); ALUOutput -> branch target BEQZ: comparison against 0

  17. EX IFID EX MEM WB • Execution/effective address cycle -Branch ALUOutput ← NPC + (Imm<<2); Cond ← (A == 0); ALUOutput -> branch target BEQZ: comparison against 0 Why <<2? http://www.cs.umd.edu/class/sum2003/cmsc311/Notes/Mips/addr.html

  18. MEM IFID EX MEM WB • MEMory access/branch completion update PC for all instr: PC ← NPC; -Memory Access LMD ← Mem[ALUOutput]; load Mem[ALUOutput] ← B; store -Branch if (cond) PC ← ALUOutput; Load Memory Data register

  19. WB IFID EX MEMWB • Write-Back cycle -Register-register ALU instruction Regs[rd] ← ALUOutput; -Register-immediate ALU instruction Regs[rt] ← ALUOutput; -Load instruction Regs[rt] ← LMD;

  20. Put It All Together

  21. MIPS Instruction IF ID EX MEM WB IR ← Mem[PC]; NPC ← PC + 4;

  22. MIPS Instruction IF ID EX MEM WB A ← Regs[rs]; B ← Regs[rt]; Imm ← sign-extended immediate field of IR (lower 16 bits)

  23. MIPS Instruction IF ID EX MEM WB ALUOutput ← A + Imm; ALUOutput ← A func B; ALUOutput ← A op Imm; ALUOutput ← NPC + (Imm<<2); Cond ← (A == 0);

  24. MIPS Instruction IF ID EX MEM WB PC ← NPC LMD ← Mem[ALUOutput]; Mem[ALUOutput] ← B; if (cond) PC ← ALUOutput;

  25. MIPS Instruction IF ID EX MEM WB Regs[rd] ← ALUOutput; Regs[rt] ← ALUOutput; Regs[rt] ← LMD;

  26. MIPS Instruction Demo • Prof. Gurpur Prabhu, Iowa State Univ http://www.cs.iastate.edu/~prabhu/Tutorial/PIPELINE/DLXimplem.html • Load, Store • Register-register ALU • Register-immediate ALU • Branch

  27. Load

  28. Load: IF Load

  29. Load: ID Load

  30. Load: EX Load

  31. Load: MEM Load

  32. Load: WB Load

  33. Store

  34. Store: IF Store

  35. Store: ID Store

  36. Store: EX Store

  37. Store: MEM Store

  38. Store: WB Store

  39. IF Register-Register ALU: MEM

  40. IF Register-Register ALU: MEM

  41. ID Register-Register ALU: MEM

  42. EX Register-Register ALU: MEM

  43. MEM Register-Register ALU: MEM

  44. WB Register-Register ALU: MEM

  45. IFEM Register-Imm ALU:MEM

  46. IFEM Register-Imm ALU: MEM

  47. IDEM Register-Imm ALU: MEM

  48. EXEM Register-Imm ALU: MEM

  49. MEMEM Register-Imm ALU: MEM

  50. WBEM Register-Imm ALU: MEM

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