Guy, I understand that cylinder command has no particular timing requirements, while head command must be effective within microseconds. My doubt is, RAM access on high performance port could be fast enough to satisfy also the latter. In case it couldn't or was not assured, I think the best strategy could be to preload only a small block of data for each head, for prompt start on head command; enough to manage safely RAM access latency. Each block also would work as buffer for data of subsequent RAM accesses, until whole cylinder had been processed. This strategy would remove the strict requirement of blockram capacity for the Zynq, and given that bigger models cost a lot, it would be a significant spare for anybody. Furthermore, support for any hypotetical disk with bigger cylinder (not SMD) or for tape with very large blocks or "infinite" streams could not be feasible with the whole cylinder design. I would prefer to avoid any such limitation, in way to possibly reuse the same data transfer modules for any media.
Andrea
