Meaning
Processor safety mechanisms achieve lockstep operations by executing identical instruction streams on two separate processing units simultaneously to compare results. In critical industrial applications, dual core execution ensures that any discrepancy between the two processing pipelines triggers an immediate hardware exception before corrupted data can reach the system outputs. The comparison logic operates at the clock cycle level, meaning that the two cores run the same code with a fixed delay of one or two clock cycles to prevent common cause failures caused by transient voltage spikes or localized electromagnetic interference.
Redundancy Mode
Operating modes for redundant processors are split between asymmetric performance tasks and symmetric safety checks. In a lockstep redundancy mode, dual core execution forces both execution units to process the same instructions, sacrificing half of the potential compute capacity for safety. If performance is prioritized, the system shifts to an independent processing mode where the second core handles non-critical tasks like communication stacks or diagnostic logging.
Synchronization Penalty
Hardware pipelines running in lockstep demand extremely tight clock synchronization across the silicon die. When a branch misprediction or a cache miss occurs on one processing unit, both pipelines must pause to maintain their relative offset. Pipeline alignment delays introduce a performance overhead of several percentage points compared to unrestrained asymmetric processing.
Safety Certification
Functional safety standards like IEC 61508 or ISO 26262 govern the development of automotive and industrial controllers. Implementing dual core execution provides a structured path to achieving High Diagnostic Coverage, which is a requirement for Automotive Safety Integrity Level D certification. The silicon vendor must provide the developer with an official Safety Manual detailing the diagnostic coverage achieved by the lockstep architecture under worst case fault injection campaigns.
