Instead of polling for a store to a specific memory location, software registers a reservation set that includes all the bytes of the memory location using the LR instruction. A subsequent `wrs.sto` instruction would cause the hart to temporarily stall execution in a low-power state until a store occurs to the reservation set or an interrupt is observed. Sometimes the program waiting on a memory update may also need to carry out a task at a future time or otherwise place an upper bound on the wait. To support such use cases, `wrs.sto` bounds the stall duration to an implementation-define short timeout such that the stall is terminated on the timeout if no other conditions have occurred to terminate the stall. The program using this instruction may then determine if its deadline has been reached. `wrs.sto` causes the hart to temporarily stall execution in a low-power state as long as the reservation set is valid and no pending interrupts, even if disabled, are observed. For `wrs.sto` the stall duration is bounded by an implementation defined short timeout. These instructions are not supported in a constrained LR/SC loop. Hart execution may be stalled while the following conditions are all satisfied: a. The reservation set is valid b. If `wrs.sto`, a "short" duration since start of stall has not elapsed c. No pending interrupt is observed (see the rules below) While stalled, an implementation is permitted to occasionally terminate the stall and complete execution for any reason. `wrs.sto` follows the rules of the WFI instruction for resuming execution on a pending interrupt. Since `wrs.sto` can complete execution for reasons other than stores to the reservation set, software will likely need a means of looping until the required stores have occurred. [Note] The duration of a `wrs.sto` instruction's timeout may vary significantly within and among implementations. In typical implementations this duration should be roughly in the range of 10 to 100 times an on-chip cache miss latency or a cacheless access to main memory.
wrs.stoType: