Reliability and safety are mandatory requirements for safety-critical embedded systems. The design of a fault-tolerant system is required in many fields (e.g., railway, automotive, avionics) and redundancy helps in achieving this goal. Redundant systems typically leverage voting techniques applied to the outputs produced by tasks to detect and even tolerate failures. This paper studies the integration of distributed voting protocols in fixed-priority real-time systems from a scheduling perspective. It analyzes two scheduling strategies for implementing voting. One is attractive and friendly for software developers and based on suspending the task execution until the replica provides the data to be voted. The other one is inspired by the Logical Execution Time (LET) paradigm and requires introducing additional tasks in the system to accomplish voting-related activities. Queuing and delays introduced by inter-replica communication interfaces are also analyzed. Experimental results are finally presented to compare the two strategies, showing that LET-inspired voting is much more predictable and hence more suitable than the other strategy for fixed-priority real-time systems.

Almost all functional safety standards that regulate safety-critical domains impose to periodically test hardware platforms at run-time. RAM memories are among the fundamental components of computing platforms and are notably subject to faults. Hence, they are also primary components to be tested. Unfortunately, RAM tests are destructive, require to be atomically executed, and are not cheap from a computational perspective. As such, if not properly managed, they can jeopardize the timing performance of a real-time system, especially when running upon a multicore platform.This paper proposes a software architecture to integrate online memory tests on multicore real-time systems. Furthermore, by jointly considering a task model and a safety model based on the EN50129 safety standard, it presents an approach to compute the optimal configuration of memory tests that preserves the system schedulability and guarantees a given tolerable functional failure rate (TFFR). Experimental results show that the proposed approach allows achieving a marginal impact on schedulability while preserving a TFFR that is compatible with the highest safety integrity level specified by the EN50129.