Carlos Arthur Lang Lisbôa, Erik Schüler , Luigi Carro SRC TechCon 2005

1. Dealing with Multiple Simultaneous Faults in Future Technologies INFORMÁTICA Carlos Arthur Lang Lisbôa, Erik Schüler , Luigi Carro SRC TechCon 2005 Who cares about multiple simultaneous transient faults ? TMR can not withstand multiple upsets wrong output V O T E R Module 1 correct output wrong output Module 3 1 0 1 0 0 0 0 1 1001000100001011 Single Event Upset Origin 1000000100001010 1000100110011010 wrong output Stochastic Multiplier Circuit Module 3 0 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 111111111111111111111111111111111110000000...0000(35 1s) 01100010101 S1 010111011001 sum S3 0010100110101 111111111111111111111010101010101010000000...0000(28 1s) S2 01010101101 Stochastic Adder Circuit 111111111111111111110000000000000000000000...0000 (21 1s) • the precision of the output stream generated by the multiplier depends heavily on the stream length • short streams (with few samples) did not produce precise results • this operator has been used to implement a FIR filter (see figures bellow) and, for this specific application, did not produce enough precision 2 x count of 1s in the output = 56 Stochastic Adder Operation with pS3 = 0.5 Porto Alegre - RS BRAZIL Phone +55 51 33166155 e-mail calisboa@inf.ufrgs.br eschuler@eletro.ufrgs.br carro@eletro.ufrgs.br % Errors in 1,000 additions 8,192 samples 1,048,576 samples Output of FIR Filter Using Stochastic Operators Universidade Federal do Rio Grande do Sul - UFRGS Instituto de Informática, Pós-Graduação em Ciência da Computação Grupo de Microeletrônica (GME) Laboratório de Sistemas Embarcados (LSE) http://www.inf.ufrgs.br/gme, http://www.inf.ufrgs.br/~lse Future technologies, bellow 90nm, will present transistors so small that they will be heavily influenced by electromagnetic noise and SEU induced errors. Since many soft errors might appear at the same time, a different design approach must be taken. • Motivation • propagation delays will be shorter than transient pulses duration • smaller transistors will be more sensitive to • electromagnetic noise • neutron and alpha particles Using Stochastic Operators(1) Due to the random nature of SEU induced transient errors, stochastic operators have been chosen to implement one adder and one multiplier that could withstand multiple soft errors. Instead of adding or multiplying binary coded values, those devices operate on bit streams, whose probabilities (% of bits equal to 1 in the stream) are related to the values of the operands. There is an intrinsic approximation error in the conversion, which decreases as the number of bits in the stream increases, and can be regarded as noise. Comments • Despite the low speed obtained in the simulation of a FIR Filter using the stochastic adder and multiplier, we believe that the use of signal redundancy may lead to other interesting approaches • Also, the idea of taking component variability into account during design may succeed, once the adequate granularity to apply this approach is reached • In order to confirm those assumptions, new experiments are being developed in our research group (1) Lisbôa, C. and Carro, L., “An Intrinsically Robust Technique for Fault Tolerance under Multiple Upsets ”, in Proceedings of the 10th IEEE International Online Test Symposium - IOLTS 2004, pp. 180, IEEE Computer Society, New York, July 2004.