Hewlett-packard Company

Thomas B Alexander

Kenneth K Chan

Edward M Jacobs

Robert E Naas

Julie W Wu

A computer system has a multi-tiered bus system. The multi-tiered bus system includes one or more local buses and a central bus connected to each local bus by a bus interface. In order to maintain one global view of transaction ordering, the processors on each local bus record bus transactions in an order on which the bus transactions appear on the central bus. To do this, bus transactions which are initiated on any local bus are forwarded to the central bus by the corresponding bus interface. The processors connected to the local bus do not record bus transactions when they are initiated on the local bus. Every transaction which occurs on the central bus is echoed back to every local bus by the corresponding bus interface. Each processor records bus transactions at the time they are echoed back to the local bus.

Coherent transaction ordering in multi-tiered bus system

The present invention provides a protocol method for waiting the bus in a digital computer and an apparatus for implementing that protocol. By allowing the bus to continue running after a wait command has been asserted, modules on the computer bus are not required to respond instantly to the wait command. Information on the bus during the multiple cycles of the wait period is defined as invalid and valid data is driven on the bus after the wait period has expired. Bus driver modules are provided with a replay queue to replay, on the bus, data the driver module drove on the bus during the wait period if required.

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Santa Clara, CA, United States of America

Thomas B Alexander