Abstract: A distributed system structure for a large-way, symmetric multiprocessor system using a bus-based cache-coherence protocol is provided. The distributed system structure contains an address switch, multiple memory subsystems, and multiple master devices, either processors, I/O agents, or coherent memory adapters, organized into a set of nodes supported by a node controller. The node controller receives transactions from a master device, communicates with a master device as another master device or as a slave device, and queues transactions received from a master device. Since the achievement of coherency is distributed in time and space, the node controller helps to maintain cache coherency. A transaction tag format for a standard bus protocol is expanded to ensure unique transaction tags are maintained throughout the system. A sideband signal is used for intervention and Reruns to preserve transaction tags at the node controller in certain circumstances.

Abstract: A distributed system structure for a large-way, symmetric multiprocessor system using a bus-based cache-coherence protocol is provided. The distributed system structure contains an address switch, multiple memory subsystems, and multiple master devices, either processors, I/O agents, or coherent memory adapters, organized into a set of nodes supported by a node controller. The node controller receives commands from a master device, communicates with a master device as another master device or as a slave device, and queues commands received from a master device. Due to pin limitations that may be caused by large buses, e.g. buses that support a high number of data pins, the node controller may be implemented such that the functionality for its address paths and data paths are implemented in physically separate components, chips, or circuitry, such as a node data controller or a node address controller.

Abstract: A method of transferring data between devices in a computer system. In a preferred embodiment, a requesting device broadcasts a request for data to other devices in the computer system. The computer system identifies, from a plurality of responding devices within the computer system, a target device that contains the data. In response to a determination that the target device does not support higher-performance transactions, the computer system disables higher-performance transactions and transfers the data to the requesting device via a lower-performance transaction process.

Abstract: A method for transferring data between devices in a computer system. In a preferred embodiment, a requesting device broadcasts a request for data. Each of a plurality of devices within the computer system responds to the request and indicates the location of the device and whether the device contains the requested data. The data is then transferred to the requesting device from one of the devices containing the data within the plurality of devices to the requesting device. The device selected to transfer the data to the requesting device has the closest logical proximity to the requesting device which results in a quick transfer of data.

Abstract: A method and apparatus in a data processing system having a plurality of node controllers and a memory unit for each of the node controllers. Each one of the node controllers including at least one processor having a cache. Each memory unit including a plurality of entries each having an exclusive bit, an address tag, and an inclusion field. Each bit of the inclusion field representing one of the node controllers. The method and apparatus allow error recovery for errors occurring within the entries without using the ECC implementation. Specifically, two parity bits are used for detecting errors within an entry and logic for flushing any cache lines represented by the entry in error. The method and apparatus also includes means for detecting persistent errors and for indicating whether the error is generated by either hardware or software.

Abstract: An arbitration protocol, preferably known as data-valid extended (DVE) protocol, for determining which one of the two units within a computer system may obtain access to a common bus is described. The DVE protocol is based on a point-to-point communication between two peer units. The DVE protocol is a physical level signalling convention for controlling switch communications on bi-directional address buses and data buses in a boundary-latched synchronous environment. The DVE protocol is asymmetric, yet fair, and is designed to minimize the number of cycles spent (or latency) in accessing the address or data buses and to maximize the number useful cycles (or bandwidth) on the address buses as well as the data buses. The asymmetry of the DVE protocol reduces the number of cycles spent in arbitration to zero for any data transfer size greater than one.