Sv2 separates mining prevhash and future job, vs the combined message in Sv1 which forces pools to send empty blocks to communicate a prevhash. Sv2 pools can send jobs to workers ahead of time for future blocks, even before the prior block has been found. Pools send the latest prevhash in a space opitimized message, starting the end-device mining on the next block in a single 32-byte message.