Lockheed Martin Corporation

Steven Allen Murrphy

Donald B Bennett

The Scalable Coherent Interface (SCI) standard of the Institute of Electrical and Electronics Engineers is intended for fast, high throughput, point-to-point, unidirectional links to high-performance multiprocessor systems. Key elements of the protocol for SCI are the (a) idle.cc which are idle bits circulation to be inserted between packets transmitted in an SCI network for detecting lost packets which toggles when the idle bit circulation has circulated around the ringlet; and (b) idle.ac, or allocation bit which is a bit in a group of transmitted idle bits which toggles when all operational nodes in an SCI network have had an opportunity to transmit their data packets. All switches accumulate transitions of the allocation bits to a value that is different from the current remembered allocation value on each enabled input port. If the network is out of allocation bit synchronization at a switch when a second transition of allocation bit occurs on an input port of the switch, the transition is ignored. The switch declares agreement when all input ports have made at least one transition even though the current allocation bit values at the input ports are not in agreement. This procedure allows rows that are one idle allocation value behind to advance their value while preventing the other rows from advancing their value, which enables resynchronization of idle allocation values after network idle allocation synchronization has been lost. All non-output stage switches toggle the current value of the allocation bit when all enabled output ports of the switch have transmitted the current allocation bit value and all enabled input ports have transitioned as explained above. This guarantees that the current agreement is broadcast on all output ports before a new value allocation can be accepted.

Allocation of node transmissions in switching networks used with

The Scalable Coherent Interface (SCI) standard of the Institute of Electrical and Electronics Engineers is intended for fast, high throughput, unidirectional links to high performance microprocessor systems. Key elements of the protocol for SCI include: (a) a 'new/stale' bit which is generated in a data packet for detecting stale packets to discard; (b) a scrubber node in each operational ring of an SCI network which toggles 'new/stale' bits from a 'new' state to a stale state when they are received at the scrubber node. In addition, valid ring identity code bits are used to identify operational rings and target identity code bits are used to identify the intended designated target mode of each packet. Packets are transmitted from input ports to output ports of the switches and through operational rings of the network that are connected until each of the packets reaches a designated target node. Each of the packets includes a 'new/stale' bit which is set to a 'new' state when a packet is generated in a source node in a first operational ring for transmission to a target node in a second operational ring. The target node may be the same as the first node. Scrubber nodes receive the packets and toggles a 'new/stale' bit that is set to a 'new' state to its 'stale' state at the output of the scrubber node. Ring identity code bits at each switch of the input stage are used to identify each of the operational rings. Target identity code bits included in each packet are compared with ring identity code bits that are associated with the input ports of the input stage switches. The 'new/stale' bit of each misrouted packet is reset to a 'new' state which arrives at an input operational stage switch when a comparison of the target identity code bits and the ring identity code bit does not occur, and otherwise the 'new/stale' bit in each packet is left in a stale state if the comparison does occur. The packet is eliminated at the next scrubber node in an operational ring when its 'new/stale' it is in its 'stale' state.

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Apple Valley, MN, United States of America

Steven Allen Murrphy