Emulated Cycle Steal Optimization in Inbound Operations
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
This article describes the use of some internal commands which, by a different sequencing, improve performance of cycle steal (inbound) operations between a PROCESSOR and an ADAPTER. As shown in Fig. 1, the PROCESSOR and ADAPTER are linked together by an EXTERNAL BUS on which are exchanged data (halfwords or bytes - last transfer only). Exchanges on the EXTERNAL BUS are controlled by tags: - TD = data request (controlled by PROCESSOR) - VH = data ready (controlled by ADAPTER - current halfword) - EOC = data ready (controlled by ADAPTER - last halfword) - VB+M = data ready (controlled by ADAPTER - last byte) A hand-shaking protocol is used between TD and VH, EOC or VB+M. The PROCESSOR is organized around three hardware entities: processing unit, storage adapter and external bus adapter.