Paper by F.L. Kastensmidt, G. Neuberger, L. Carro, R. Reis Talk by Nick Boyd 1

 Exploring techniques for detecting and dealing with radiation-induced faults in FPGAs  Why?  Drive to use commercial off-the-shelf to minimize cost and development time (for space apps)  As technology gets smaller, radiation becomes an issue even at ground level 2

 Incident radiation deposits energy  creation of electron-hole pairs and secondary ionizations produce transient current pulse  Can change a ‘0’ to a ‘1’ or vice versa, often called “bit flip”  In combinational logic: Single Event Transient (SET)  In sequential (or memory): Single Event Upset (SEU) 3

 In FPGAs there are further considerations  SEU in the configuration SRAM (logic, routing)  SET in combinational FPGA fabric  SEU in BlockRAM 4

 Effects of SEU in configuration fabric 5

 TMR = Triple Modular Redundancy  Logic is triplicated and results are accepted by majority vote  Everything is tripled; including combinational, sequential, routing and i/o 6

 Benefits  Able to detect and correct SEU\SET anywhere in the FPGA  No performance penalty  Drawbacks  Very large area/resource penalty (particularly problematic for i/o pads) 7

 A new technique proposed by the authors of this paper  DMR-CED: Double Modular Redundancy with Concurrent Error Detection  Motivation: Want to find a way that is as reliable as TMR in detecting/correcting errors with less area overhead 8

 CED = Concurrent Error Detection  Exploits some property of the logic block to find error  Time-redundant examples:  bit-wise inversion  re-computing with shifted operands (RESO)  re-computing with swapped operands (REWSO) 9

 Result calculated from direct input and stored  Input then encoded, new result calculated and decoded  Two outputs compared – should be equal 10

 How can we use CED?  Only duplicate combinational logic  Use CED to determine the faulty module only if there is disagreement 11

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 Three sample sequential circuits tested  8-bit multiplier  8-bit ALU  FIR filter  Sample circuits generated then each node was replaced with a multiplexor which either passes ‘correct’, ‘0’, or ‘1’  Able to simulate every possible SEU fault 13

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 Benefits  Reduces area required for combinational logic (by a significant amount in some cases)  Drawbacks  Significantly more complicated due to CED  CED circuit needs to be chosen to be optimized for each combinational circuit you protect  Speed reduced by as much as 50% 16

 Reasonably well written and complete  Necessary to read the references to understand the minutiae of underlying principles  DMR-CED probably only useful under very specific conditions 17