Safety in Reset
Overview
Reset logic establishes the initial conditions of a digital system and ensures that all functional blocks start from a known, valid, and synchronized state. Because reset affects every register, state machine, and control path, faults in the reset network can propagate instantly and unpredictably.
Safety analysis focuses on ensuring that reset signals are clean, synchronized, glitch‑free, and robust against noise, timing faults, and partial activation.
This page describes the safety‑relevant aspects of reset generation, distribution, synchronization, and supervision.
Scope
This page focuses on safety‑relevant failure modes and mitigation strategies in reset generation, distribution, and supervision. Architectural and implementation details are covered in the technical reset pages listed below.
Main Safety Risks
Asynchronous Reset Glitches
Spurious pulses may cause partial or unintended resets, leading to unpredictable system behavior.
Incomplete Reset Propagation
Some registers may reset correctly while others remain in undefined states, causing illegal logic combinations.
Reset Domain Crossing (RDC) Faults
Crossing reset signals between clock domains can introduce metastability or misalignment.
Stuck‑Active or Stuck‑Inactive Reset
Logic faults or wiring issues may permanently assert or deassert reset.
Brown‑Out or Power Instability
Supply dips may trigger partial resets or corrupt internal state.
Reset Sequencing Errors
Incorrect order of subsystem resets may lead to invalid initialization.
Reset Release Timing Faults
Registers exiting reset at different times may cause FSM corruption or illegal states.
I/O‑Related Upstream Faults
External reset pins may be affected by noise, EMI, or short‑to‑ground/battery.
State Machine Corruption on Reset Release
Unsynchronized reset deassertion may cause FSMs to enter undefined states.
Mitigation Techniques
Synchronized Reset Release
Ensure reset deassertion is aligned with the destination clock domain.
Glitch Filtering
Debounce and filter external reset inputs to avoid false triggers.
Reset Stretching
Guarantee minimum reset pulse width for all registers.
Reset Sequencing
Control the release order for dependent subsystems.
Redundant Reset Paths
Use dual reset sources or monitored reset controllers for high‑integrity systems.
Power‑On Reset (POR) Supervision
Detect brown‑out, undervoltage, or unstable supply conditions.
Reset Domain Crossing Checks
Verify that reset signals crossing domains are synchronized and safe.
Built‑In Self‑Test
Validate reset controller logic and reset distribution at startup.
ATPG/DFT Support
Provide scan‑based observability of reset trees and measure fault coverage.
Related Technical Pages
- Reset — Architecture and Distribution
- Reset — Asynchronous vs Synchronous Strategies
- Reset — Sequencing and Power‑On Initialization
- Clock Domain Crossing — Architecture & Fundamentals
- Clock Domain Crossing — Practical Guidelines
- Clocking — Gating, Distribution, and CDC
