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Analytical Approach for Soft Error Rate Estimation of SRAM-Based FPGAs

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Presentation on theme: "Analytical Approach for Soft Error Rate Estimation of SRAM-Based FPGAs"— Presentation transcript:

1 Analytical Approach for Soft Error Rate Estimation of SRAM-Based FPGAs
Ghazanfar (Hossein) Asadi Test & Reliability Group (TRG) Department of Electrical & Computer Engineering Northeastern University

2 Problem Statement Estimating soft error rate in FPGAs
The probability of system failure Due to soft errors For a given mapped design Mean time to manifest a corrupted conf. bit To primary outputs or Flip-flops Test & Reliability Group (TRG)

3 Motivation Need for soft error rate estimation
Exponential growth of vulnerable bits due to Moore’s law High cost of Error tolerant schemes To make appropriate cost/reliability trade-offs Where to put redundancy Previous work: Fault Injection Time-consuming / Incomplete / Expensive Needs physical prototype board Cannot be used in design phases Prototype board can be damaged  Hard Error Test & Reliability Group (TRG)

4 Error Models in FPGAs Memory resources: User bits  Transient errors
Flip-flops, RAMs, … Configuration bits Mux select bits, LUT bits, PIPs, … User bits  Transient errors Config. bits  Permanent errors Test & Reliability Group (TRG)

5 SER Estimation Traversing structural paths [Asadi04]
From error sites to outputs Test & Reliability Group (TRG)

6 SER Estimation in ASIC Designs
S(n): System failure probability (SFP) vector Si: SFP given node i erroneous n: total fault sites Experiments on ISCAS89 show that: Three order of magnitude faster Compared to random-input simulation Accuracy: more than 90% Test & Reliability Group (TRG)

7 FPGA vs. ASIC in SER Estimation
ASIC: transient error Only requires propagation probability FPGA: both transient & permanent errors Transient errors: the same Permanent errors: needs activation as well More error sites in FPGAs Routing signals Test & Reliability Group (TRG)

8 FPGA vs. ASIC in SER Estimation
Nodes with different error rates in FPGAs No attenuation in FPGAs During propagation Test & Reliability Group (TRG)

9 SER Estimation of FPGAs: Steps
Compute permanent error rates for all nodes PRi : the permanent error rate of node i n: total number of fault sites Compute netlist failure probability vector Ni= failure prob. given node i erroneous System failure rate vector (S) = PR  N Si = PRi  Ni Test & Reliability Group (TRG)

10 How to Compute Ni? Open & stuck-at errors:
Ni = [SPi  PPi(0) + (1-SPi)  PPi(1)] = PPi PPi: Propagation prob. (the method used for ASIC) SP: Signal probability is used for activation prob. Bridging wired-AND & wired-OR error (nets i and j): Ni (Wand)= [SPi(1-SPj)PPi(0)] + [(1-SPi) SPjPPj(0)] Ni (Wor)= [SPi(1-SPj)PPj(1)] + [(1-SPi) SPjPPi(1)] LUT bit-flip: Ni = Activation prob. (cell)  Prop. Prob. (LUT output) Test & Reliability Group (TRG)

11 How to Compute PRi? PR(n): permanent error rate vector PRi : r  f
r: Raw error rate of an SRAM cell f: Number of all possible errors at node i n: total number of error sites PRAB= 6  r Test & Reliability Group (TRG)

12 System Failure Rate For the first clock: For c clock cycles:
The same probability is valid for the next clock cycles c: Number of clocks checking the state of the circuit After particle hit Test & Reliability Group (TRG)

13 Error List Mux-open PIP open Buffer off A bit-flip in LUT
Control/clocking bit-flip Test & Reliability Group (TRG)

14 Experimental Setup Xilinx Virtex 300 (XCV300)
Xilinx Design Language (XDL) Benchmark: some ISCAS89 circuits r = raw failure rate for an SRAM cell r=0.01 FIT/bit 1000 clocks executed for each SEU Platform: Sun Solaris Ultra-10 256 MB Main Memory Test & Reliability Group (TRG)

15 Results: Sensitive Bits
Number of sensitive SRAM bits for each part Circuit S27 S298 S344 S349 s382 s386 Routing 64 459 536 650 807 714 LUT 68 418 392 520 712 660 Control/ Clocking 40 140 168 187 207 160 Total 172 1017 1096 1357 1726 1534 Test & Reliability Group (TRG)

16 Results: SFR & Estimation Time
System Failure Rate & Estimation Time Circuit S27 S298 S344 S349 s382 s386 SFR (FIT) 1.71 9.87 9.99 12.77 16.04 12.11 SP Time (sec) 0.15 0.76 0.91 1.09 1.25 1.05 SFR Time (sec) 0.02 0.09 0.13 0.14 0.19 0.25 Total Time (sec) 0.17 0.85 1.04 1.23 1.44 1.30 Number of Clock cycles: 1000 SP Time: Signal Probability computation time SFR Time: System Failure Rate computation time Test & Reliability Group (TRG)

17 Results: Manifestation Time
Mean Time To Manifest (MTTM) errors to outputs Circuit S27 S298 S344 S349 s382 s386 Routing 2.07 2.86 2.58 2.91 3.30 3.82 LUT 14.49 20.75 17.33 20.48 22.08 30.07 Control/ Clocking 1.18 1.31 1.36 1.40 1.77 (Results are in terms of cycles) Test & Reliability Group (TRG)

18 Summary & Conclusions A new approach for SER estimation
For SRAM-based FPGAs No physical implementation required Can be used in early design stages Very fast simulation time Can cover all possible faults Mean Time To Manifest errors to outputs: MTTM(Control/clocking) < MTTM(routing) MTTM(routing) << MTTM(LUT) Test & Reliability Group (TRG)

19 Questions? Thanks Test & Reliability Group (TRG)


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