Multi cycle DataPath

Transcript

1. 36 One Alternative to Single-Cycle DP: Multi-Cycle DP • Cuts datapath into multiple stages (5 here), isolated using registers • FSM control “walks” insns thru stages (by staging control signals) + Insns can bypass stages and exit early P C Insn Mem Register File S X s1 s2 d Data Mem a d + 4 << 2 I R D O B A s3 s3 s3 s4 s5 s5 s5
2. 46 Multi-Cycle Datapath Example: Add P C Insn Mem Register File S X s1 s2 d Data Mem a d + 4 << 2 I R D O B A • Example: Add • Cycle 1: Read IMEM
3. 47 Multi-Cycle Datapath Example: Add P C Insn Mem Register File S X s1 s2 d Data Mem a d + 4 << 2 I R D O B A • Example: Add • Cycle 1: Read IMEM • Cycle 2: Decode + Read RF
4. 48 Multi-Cycle Datapath Example: Add P C Insn Mem Register File S X s1 s2 d Data Mem a d + 4 << 2 I R D O B A • Example: Add • Cycle 1: Read IMEM • Cycle 2: Decode + Read RF • Cycle 3: ALU
5. 49 Multi-Cycle Datapath Example: Add P C Insn Mem Register File S X s1 s2 d Data Mem a d + 4 << 2 I R D O B A • Example: Add • Cycle 1: Read IMEM • Cycle 2: Decode + Read RF • Cycle 3: ALU • Cycle 4: Writeback + Increment PC
6. 50 Multi-Cycle Datapath Performance • Opposite performance split of single-cycle datapath + Short clock period – High CPI P C Insn Mem Register File S X s1 s2 d Data Mem a d + 4 << 2 I R D O B A