"Zawrs": Wait-on-Reservation-Set

PAUSE throttles a spin loop; Zawrs parks it. The idiom turns the cache-coherence protocol into a doorbell: take an LR on the watched location to register a reservation set, then WRS stalls the hart in low power until something invalidates that reservation — i.e., until the store you were polling for actually happens.

# consumer waiting on queue tail (futex-style, any privilege mode)
retry:
    lr.d    t0, (a0)          # register reservation on the flag
    bnez    t0, ready         # already set? done
    wrs.nto                   # sleep until a store hits the line,
    j       retry             #   an interrupt pends, or spuriously
ready:

The stall persists only while all hold: the reservation set is valid, no interrupt is pending (even a globally-disabled one — the WFI observation rule), and, for STO, the short timeout (guidance: 10–100× a cache-miss latency) hasn’t lapsed. Implementations may end the stall spuriously at any time — the loop is mandatory.