Priority logic for selecting and stacking data

Abstract

A method and apparatus for setting a priority sequence among a plurality of requesters using a common destination within a computer system. An advantage is that all requesters contending for the common destination will have timely access with respect to all other competing requesters. In a first exemplary embodiment of the present invention, a priority controller can use a two-level priority scheme to select the next requester. The first level of priority alternates between an external requester and an on-card requester where every other set of data is from the external requester. The second level of priority alternates between on-card modules during an on-card priority cycle. In an alternative exemplary embodiment, the priority controller can stack a request to transfer acknowledge and data information from an external requester if it is busy. The priority controller also prevents sending an acknowledgment/data cycle out to an external source to prevent sending more data than the FIFO stacks can accommodate. The data may also consist only of acknowledgements.