SEU Mitigation Techniques for Microprocessor Control Logic

The importance of fault tolerance at the processor archi- tecture level has been made increasingly important due to rapid advancements in the design and usage of high per- formance devices and embedded processors. System level solutions to the challenge of fault tolerance flag errors and utilize penalty cycles to recover through the re-execution of instructions. This motivates the need for a hybrid tech- nique providing fault detection as well as fault masking, with minimal penalty cycles for recovery from detected er- rors. We propose three architectural schemes to protect the control logic of microprocessors against Single Event Up- sets (SEUs). High fault coverage with relatively low hard- ware overhead is obtained by using both fault detection with recovery and fault masking. Control signals are classified as either static or dynamic, and static signals are further classified as opcode dependent and instruction dependent. The strategy for protecting static instruction dependent con- trol signals utilizes a distributed cache of the history of the control bits along with the Triple Modular Redundancy (TMR) concept, while the opcode dependent control signals are protected by a distributed cache which is used to flag errors. Dynamic signals are protected by selective dupli- cation of datapath components. The techniques are imple- mented on the OpenRISC 1200 processor. Our simulation results show that fault detection with single cycle recovery is provided for 92% of all instruction executions. FPGA synthesis is performed to analyze the associated cycle time and area overheads.