Sample Use of LL-SC

lock: ll R1, Loc -- Load-lock Loc to R1

bnz R1, lock -- Spin if Loc locked

sc Loc, R2 -- Cond’ly store R2 in Loc

beqz lock -- If failed, repeat

ret

and

unlock: st Loc, #0 -- Clear location

ret

• Many processes can do an LL at once, but only the first to the SC wins

Previous slide

Next slide

Back to first slide

View graphic version