Carlos Arthur Lang Lisbôa, Erik Schüler, Luigi Carro SRC TechCon 2005 Dealing with Multiple Simultaneous Faults in Future Technologies in Future Technologies INFORMÁTICA 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) Porto Alegre - RS BRAZIL Phone 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) Stochastic Adder Circuit S1S1 S3S3 S2S2 sum (35 1s) (21 1s) (28 1s) 2 x count of 1s in the output = 56 Stochastic Adder Operation with p S 3 = 0.5 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. 8,192 samples 1,048,576 samples Output of FIR Filter Using Stochastic Operators % Errors in 1,000 additions Stochastic Multiplier Circuit  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 (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 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 Single Event Upset Origin Who cares about multiple simultaneous transient faults ? TMR can not withstand multiple upsets Module 1 Module 3 VOTERVOTER wrong output Module 3 correct output wrong output