Local Ring Interface

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Local Ring Interface

A block diagram of the local ring interface is depicted in Figure 11. Its upward path (to the ring) consists of a packet generator, an output FIFO, and a latch. The packet generator transforms incoming bus transactions into one or more ring packets and places them into the output FIFO. If the message must be split into multiple packets, then a distinct tag is assigned to each outgoing packet to enable re-assembly at the destination. Packets in the output FIFO are placed onto the ring as slots become available.

Figure 11: Local Ring Interface.

The downward path consists of an input FIFO, a packet handler, a sinkable queue, and a nonsinkable queue. The input FIFO is used as a buffer between the high speed ring and the packet handler. Since a slotted-ring protocol is used to transfer packets on rings, a cache line is not necessarily transferred in packets that occupy consecutive slots. As a result, the packet handler's primary task is to reassemble messages, such as cache lines, based on the tags assigned when the ring packets were sent.

Stephen D. Brown
Wed Jun 28 18:34:27 EDT 1995