Reconfigurable ECO Cells for Timing Closure and IR Drop Minimization. TingTing Hwang Tsing Hua University, Hsin-Chu

Transcription

1 Reconfigurable ECO Cells for Timing Closure and IR Drop Minimization TingTing Hwang Tsing Hua University, Hsin-Chu 1

2 Outline Introduction Engineering Change Order (ECO) Voltage drop (IR-DROP) New design style Cell level Chip level New design style for ECO flow RECON ECO algorithm Experimental results Conclusions 2

3 Outline Introduction Engineering Change Order (ECO) Voltage drop (IR-DROP) New design style Cell level Chip level New design style for ECO flow RECON ECO algorithm Experimental results Conclusions 3

4 Engineering Change Order (ECO) Incremental change of a design To fix bugs To meet timing constraint To meet small change of functionality Small modification instead of redesign a circuit To save the reiteration of design flow To reduce the cost of mask-making 5

5 Spare Cells in ECO Spare cells (NOT, NOR, NAND) are placed evenly in layout at physical design Spare cells are then used for modification in ECO flow 6

6 Outline Introduction Engineering Change Order (ECO) Voltage drop (IR-DROP) New design style Cell level Chip level New design style for ECO flow RECON ECO algorithm Experimental results Conclusions 7

7 Voltage Drop Power source fluctuations become serious High performance Lower supply voltage VDD/GND variations Chip speed Noise margin Adding decoupling capacitance (decap) is an effective way to reduce power noise [Sachin, TCAD 2003] 8

8 New ECO Design Flow A new reconfigurable (RECON) cell structure Served as spare cell and decoupling capacitor Leakage reduction Free selecting of function type Demonstration of RECON cell by an ECO algorithm for timing closure and IR drop minimization 11

9 Outline Introduction Engineering Change Order (ECO) Voltage drop (IR-DROP) New design style Cell level Chip level New design style for ECO flow RECON ECO algorithm Experimental results Conclusions 12

10 RECON Base Cell Two PMOS transistor with same transistor width Two NMOS transistor with same transistor width Eight CONTACTs VDD and GND implemented by layer of metal-1 13

11 DECAP Cell VDD VDD GND GND Schematic of cell Configured from RECON base cell Use Metal-1 connection 15

12 Functional Cell (a) Inverter (b) 2-Input NAND (c) 2-Input NOR Configured from RECON base cell 16

13 Comparisons Between RECON Cells and Standard Cells Setup of experiment Cell layouts created with TSMC 0.13um process SPICE net-lists extracted by RCextractor Delay, leakage, internal power and input pin capacitance by SPICE simulation 17

14 As Decoupling Cells Less flexibility of layout 16%-39% capacitance 9%-34% leakage 18

15 As Functional Cells Area Delay Leakage w/o tie-cell w/i tie-cell Recon w/o tie-cell w/i tie-cell Recon Power Pin cap INVX INVX INVX INVX INVX ND2X ND2X NR2X NR2X BUFX BUFX BUFX BUFX Average

16 Outline Introduction Engineering Change Order (ECO) Voltage drop (IR-DROP) New design style Cell level Chip level New design style for ECO flow RECON ECO algorithm Experimental results Conclusions 21

17 Model of Power Supply Analysis Cycle-based time frame 22

18 Model of Power Supply Analysis (cont.) Metal layer of VDD and GND modeled as a power-grid resistance Standard cells modeled as time-varying current source RECON DECAP cells modeled as capacitors connected between VDD and GND 23

19 Model of Power Supply Analysis (cont.) Supply voltage variation can be derived as following Clock cycle is divided into many time slots Switching gate are derived from static timing analysis Maximum current consumption are calculated in each time slot. 24

20 IR Drop Analysis of Whole Chip 26

21 Leakage Analysis of Whole Chip 27

22 Outline Introduction Engineering Change Order (ECO) Voltage Drop (IR-DROP) New design style Cell level Chip level New design style for ECO flow RECON ECO algorithm Experimental result Conclusion 28

23 Differences Between RECON and Traditional ECO Flows RECON DECAP instead of spare cells are pre-placed RECON DECAP cells are reconfigured to RECON functional cells when RECON ECO flow is performed Unselected RECON DECAP cells are kept as decoupling capacitors 29

24 Problem Formulation An ECO path is a path that violates the timing constraint Given a set of placed gate level net-list, ECO paths and timing constraint, perform gate sizing or buffer insertion on ECO paths Timing constraint is met IR drop is minimized 30

25 RECON ECO Algorithm Input: a set of ECO paths to be optimized For each ECO path Find the critical gates in ECO paths and put in ECO_gate_list While (timing is not satisfy) Choose the gate from ECO_gate_list with most output loading Perform gate sizing or buffer insertion List_A = search_region(gate_sizing) List_B = search_region(buffer_insertion) For all configurable cell Rg in List_A or List_B If IRdrop(Rg) > threshold Remove Rg in List_A or List_B Candidate_list = List_A + List_B Compute path delay gain for all Rg in Candidate_list Select the best Rg corresponding to the best delay gain Update the ECO path delay End while 32

26 Search Region for Gate Sizing D1 D2 G5 G1 G3 G4 G7 G2 D4 D3 D5 G6 D6 Search_region(G4) = Bounding_Box(G3 U G4 U G5 U G6) 33

27 Search Region for Buffer Insertion D1 D2 G5 G1 G3 D3 G4 D5 G7 G2 D4 G6 D6 Search_region(G4) = Bounding_Box(G4 U G5 U G6) 34

28 Outline Introduction Engineering Change Order (ECO) Voltage drop (IR-DROP) New design style Cell level Chip level New design style for ECO flow RECON ECO algorithm Experimental results Conclusions 35

29 Experimental Setup ITC99 benchmarks Benchmarks synthesized to gate-level net-list using TSMC 0.13um process Standard cells and RECON DECAP cells placed by SOCEncounter 20% area used to place RECON DECAP cells 36

30 Experimental Flow 37

31 Statistics of Benchmarking Circuits Timing constraint is set to 90% of critical path delay in the original circuit 38

32 Leakage (na) Leakage Comparisons Before ECO Leakage comparison with traditional spare cells with RECON DECAP cells 0 b14 b15 b20 b21 b22 benchmark set 39

33 Performance Comparisons Before ECO Trad: traditional spare cells RECON: RECON decap cells 40

34 Performance Comparisons After ECO Trad: traditional spare cells RECON: RECON decap cells 41

35 Number of Unsolved Paths After ECO Trad: traditional spare cells RECON: RECON decap cell 42

36 Conclusions A new cell structure Decoupling capacitor cell ECO spare cell A reconfigurable ECO flow 20% IR drop reduction 44% leakage reduction 43

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