Method and apparatus for controlling order dependency of items in a multiple fifo queue structure

Abstract

A barrier control scheme controls the order dependency of items in a multiple FIFO queue structure. The barrier control scheme includes a cycle ID generator, a barrier bit/barrier ID generator and a cycle ID and barrier ID comparator. Each incoming item to the FIFOs is assigned a cycle ID. If an incoming item of a first FIFO has order dependency on items of a second FIFO, a barrier bit is set and a barrier ID is determined and generated by the barrier bit/barrier ID generator. The barrier bit and barrier ID are inserted in the first FIFO along with other fields of the incoming item. When an item is to be consumed, the cycle ID and barrier ID comparator compares its barrier ID and the cycle IDs of items in the second FIFO. The item to be consumed is blocked until all items on which the item is dependent are consumed in the second FIFO.