Time model

This page describes time in the legacy Nexosim engine. The exact executor represents event time directly as u64 nanoseconds in EventKey.

Nexosim stores its monotonic simulation clock as MonotonicTime. A Simulation exposes it through time(), and model handlers can read it through Context::time(). The type is defined in crates/nexosim/src/time.rs.

Legacy integer-nanosecond boundary

Legacy configuration still expresses many durations as seconds, but the simulator converts them at the event-clock boundary in legacy/src/utils/exact_time.rs:

• Scenario-level values must resolve to a finite, nonnegative integer number of nanoseconds. Positive sub-nanosecond and fractional-nanosecond values are rejected.
• Positive sampled or controller delays are rounded up to the earliest non-early nanosecond tick.
• Packet serialization uses checked integer arithmetic and rounds positive delay up.
• clock_ns reads the exact integer offset from the Nexosim epoch.

Some legacy model fields, including Packet.time, retain an f64 seconds view for compatibility, controller calculations, and reports. That view is derived from the integer event clock; it is not a replacement for Context::time() or the authoritative event timestamp.

The legacy time_quantum setting is implemented by a Nexosim compatibility shim. Exact scenario compilation rejects a nonzero time_quantum; exact parallelism instead depends on positive channel lookahead and safe-horizon rounds.

See /docs/architecture/time-concurrency for the architecture-level comparison and /docs/internals for exact round execution.