Method and apparatus for allocating bandwidth on a loop system coupling

Abstract

A loop system couples a CPU channel to bulk storage devices via a loop controller and device adapter. The loop system is characterized by equal fixed-length, multi-byte frames, each frame of which being assignable to only one terminal at a time. The system is further characterized by having a fixed loop delay greatly exceeding the frame duration by virtue of the high data rate. Dynamically variable frame assignment occurs when the primary terminal generates an unassigned empty frame in response to each assigned full (read) frame from a secondary terminal. The primary further generates an assigned full (write) frame upon receipt of each service (write) request frame from a secondary terminal. Lastly, the primary can send access command frames for each received unassigned empty frame or any other frame that does not imply a demand for bandwidth by the secondary. Relatedly, each secondary terminal can optionally write over a frame assigned to it or should it not have a message or data to send to the primary, change the 'full' frame to 'empty', or to seize an unassigned empty frame as it passes by on the loop. The combination of secondary terminal frame reuse with that of the primary tends to distribute frame availability on a more nearly uniform basis.