Embedded systems in critical domains require both hard real-time and reliable execution. Real-time execution requires bounds in the worst-case execution time, while reliable execution is under threat, as systems are becoming more and more sensitive to transient faults. Thus, systems should be enhanced with fault-tolerant mechanisms with bounded error detection and correction overhead. Such mechanisms are typically based on redundancy at different granularity levels. Coarse-grained granularity has low comparison overhead, but may jeopardize timing guarantees. Fine-grained granularity immediately detects and corrects the error, but its implementation has increased design complexity. To mitigate this design complexity, we leverage high-level specification languages to design intrusive fine-grained lockstep processors based on the use of shadow registers and rollback, with bounded error detection and correction time, being appropriate for critical systems.