bacnet-time

The time the portable cores of rusty-bacnet share: a monotonic Instant and a Duration, both counted in nanoseconds on a u64. bacnet-mstp-core, bacnet-bip-core and bacnet-router-core take it, so firmware that runs several of them feeds them one clock.

• #![no_std], no allocator, no dependencies, no features.
• The epoch is yours: the cores read no clock, and each call that depends on time takes now. A u64 of nanoseconds lasts about 584 years.
• + and - saturate, and every operation has a checked_* form that returns None instead. Nothing panics.
• Unit constructors (from_micros, from_millis, from_secs) are const and saturate; unit accessors (as_micros, as_millis, as_secs) round toward zero.
• Conversions with core::time::Duration, so a host maps its monotonic clock onto the timeline exactly: From into it, and TryFrom back, which refuses a length past about 584 years, or the const Duration::saturating_from_core, which clamps it.
• const min and max, and a Debug with the unit: Duration(1500ns).
• No 64-bit division: on a 32-bit target, where dividing a u64 links a routine of about 1 KB, the accessors, checked_rem, the conversion to core::time::Duration and Debug use binary long division.

Example

use bacnet_time::{Duration, Instant};

// Firmware with a millisecond tick.
let now = Instant::from_millis(1_250);
let deadline = now + Duration::from_millis(500);
assert_eq!(deadline.saturating_duration_since(now).as_millis(), 500);

// Saturation, and the checked forms.
assert_eq!(Instant::ZERO - Duration::from_secs(1), Instant::ZERO);
assert_eq!(Instant::ZERO.checked_sub(Duration::from_secs(1)), None);
assert_eq!(now - deadline, Duration::ZERO);

// A host's monotonic clock, through core::time::Duration.
let elapsed = core::time::Duration::from_micros(2_500);
assert_eq!(Duration::try_from(elapsed), Ok(Duration::from_micros(2_500)));
assert_eq!(Duration::saturating_from_core(core::time::Duration::MAX), Duration::MAX);
assert_eq!(
    core::time::Duration::from(Duration::from_nanos(1_500)),
    core::time::Duration::from_nanos(1_500)
);
assert_eq!(format!("{:?}", Duration::from_nanos(1_500)), "Duration(1500ns)");

License

MIT