hal::clock

A free-running monotonic microsecond clock.

Distinct from [crate::tick::TickSource]: the tick is the periodic scheduling interrupt, counted in milliseconds; this is a free-running counter read for absolute time and for measuring intervals shorter than a tick. Not every SoC has a spare hardware counter to spend on one, so both methods default to “there isn’t one” — a SoC without a monotonic counter is answered from the scheduler tick instead, a thousand times coarser but still monotonic and correctly ordered.

Traits

MonotonicClock

trait MonotonicClock {
    unsafe fn init() -> bool
    fn now_us() -> Option<u64>
}

A monotonic microsecond clock, for the SoCs that have a spare counter.

The kernel selects one implementation and reads it through this trait, so a caller that wants absolute time names no chip. A SoC with no such counter implements nothing and takes the defaults; the kernel then falls back to the tick.