Survey of Detection, Diagnosis, and Fault Tolerance Methods in FPGAsDan Fisher, Addison Floyd

Outline

• Introduction• Fault Detection - Motivation, Methods, etc.• Fault Diagnosis - Motivation, Methods, etc.• Fault Tolerance

o Single FPGAo Multiple FPGAso Single Faultso Multiple Faults

• Conclusion

Introduction• FPGA Background• Importance• Applications• Motivation for Fault Tolerance

http://en.wikipedia.org/wiki/Field-programmable_gate_array

Fault Detection - Motivation

Main Causes of Faults• Degradation• Manufacturing Defects• Single Event Upsets(SEUs)

Fault Detection - Judgement Criteria

Detection Methods are judged on:• Speed of Detection• Coverage• Resource Overhead• Performance Overhead• Detection Granularity

Fault Detection - Criteria In-DepthDetection Granularity - how specific one is when detecting an error.

FPGA made up of Tiles containing:• Logic Blocks

• Connection Blocks - connect tiles

• Switch Blocks - connect tiles, allow for direction change

Fault Detection - Comparison

Fault Detection - SEDC Method

o The Method Explained• Partition data and Encode with SEDC codes• Calculate and Store check bits• Generate check bits as circuit operates• Compare calculated and generated values

o Better than Berger and TMR

Fault Detection - Nazar Method

• CED method providing single error detection• Takes advantage of properties of LUTs• Major Drawback - LUT insertion• Area Improvement over DWC

Nazar Method - LUT Properties Explained*

1st Advantage: A LUT can be viewed as combinational circuit independent from others. Area overhead is avoided since you don’t need to replicate sub-expressions that form circuit outputs

2nd Advantage: A K-input LUT can compute any function with up to K inputs. So as long as our selected group is no more than K different inputs than the parity can be calculated using just one LUT. If the selected group also has no more than K-1 different outputs, then the checker can be made of just one LUT(with the last input the parity bit).

This picture shows upside-down triangles as LUTs, with a one parity LUT for each K-1 outputs. Also show is the checker which would be composed of just one LUT. Separate LUTs in the same checker group can’t overlap (otherwise they wouldn’t be independent) but in order to provide coverage different checker group LUTs can overlap.

*Note:This slide wasn’t in the original presentation but was added to try to better explain the method since some mentioned wanting to know more

Fault Detection - Roving Stars

o New method for online detection o Detected faults do not affect working logico STARs and BISTERso Better than other methods

*Picture added after presentation to attempt to help

clear up any confusion.

Fault Detection - Injection Topic 1

• Which modules most sensitive to SEU• 1.4% sensitive(83% routing/16% logic)• Density matrix

Fault Detection - Injection Topic 2

• HW module to test efficiency of SEU mitigation schemes

• How to emulate SEUs - 2 step process

• Example Results

• Scrubbing Rate

Fault Diagnosis - Roving Stars

• Diagnose both interconnect & plb faults • Partial Reuse• Future - Do we allow for retest of fault?

Fault Diagnosis - More Abramovici

• BIST-based method in 2000• 2004 paper further extending Roving Stars

Fault Diagnosis - Niamat - MATS++

• Diagnose multiple stuck at faults• Use of MATS++ algorithm• Goal of speeding up diagnosis

Fault Diagnosis - Tahoori’s Method

• Diagnose a single fault in interconnect or logic

• Application Dependent• Basic Idea

Fault Tolerance

• Single FPGA platform• Multi FPGA platform• Single Fault• Multiple Faults

Fault Tolerance - Single FPGADynamic Fault Tolerance via Partial Reconfiguration

● online - handles faulty PLBs without system stopping● uses spare logic cells

Stroud et al

Fault Tolerance - Single FPGAOnline Fault Tolerance for FPGA Logic Blocks

● reuse defective blocks to increase the number of spares and extend mission life

● uses commercial CAD tools to implement

Stroud et al

Fault Tolerance - Single FPGAUsing Relocatable Bitstreams for Fault Tolerance

● combines passive and active techniques● standardized relocatable modules, which are copied

and stored

Montminy et al

Fault Tolerance - Multi FPGAA Reliable Reconfiguration Controller for Fault-Tolerant Embedded Systems on Multi-FPGA platforms

● multiple FPGAs in a mesh topology● hardening achieved by TMR● distributed solution

Bolchini et al

Fault Tolerance - Single FaultDesigning Fault Tolerant Systems into SRAM-based FPGAs

● for use in space● Duplication with Comparison and Concurrent Error

Detection

Lima et al

Fault Tolerance - Single FaultTMR and Partial Dynamic Reconfiguration to Mitigate SEU Faults in FPGAs

● passive Triple Modular Redundancy

Bolchini et al

Fault Tolerance - Single FaultIPR: In-Place Reconfiguration for FPGA Fault Tolerance

● preserves function and topology of LUT-based logic network

● algorithm applied post-layout

Zhe et al

Fault Tolerance - Single FaultA Novel SRAM-Based FPGA Architecture for Efficient TMR Fault Tolerance Support

● Architectural level● augments LUTs with TMR● minimize number of

reconfigurations

Kyriakoulakos et al

Fault Tolerance - Multiple FaultsPlacement of Repair Circuits for In-Field FPGA Repair

● utilize unused FPGA resources

● repair circuits identified before faults occur

● alternate repair circuits cached locally or remotely

Wirthlin et al

Fault Tolerance - Multiple FaultsReconfigurable Fault Tolerance: A Comprehensive Framework for Reliable and Adaptive FPGA-Based Space Computing

● dynamic self-adaptation

● high reliability vs. high performance

Jacobs et al

Fault Tolerance - Multiple FaultsExploiting Partially Defective LUTs: Why You Don’t Need Perfect Fabrication

● because of shrinking feature size, transistor variability and failure rates are going up

● identifies partially defective LUTs for reuse

DeHon et al

Conclusion

• Importance of FPGAs• FPGA applications• Future of FPGA fault tolerance

Questions?