Abstract: A method and system of expediting issuance of a second request of a pair of ordered requests into a distributed coherent communication fabric. The first request of the ordered pair is issued into the coherent communication fabric and directed to a first target. Issuance of the second request into the coherent communication fabric is stalled until the first target receives and orders the first request and transmits a response acknowledging the same.

Abstract: A node is coupled to receive a coherency command and coupled to a memory, wherein the node includes a directory configured to track a state of a first number of coherency blocks less than a total number of the coherency blocks in the memory. The directory is configured to allocate a first entry to track the state of the first coherency block responsive to the coherency command. If the first entry is currently tracking the state of a second coherency block, the second node is configured to generate one or more coherency commands to invalidate the second coherency block in a plurality of nodes.

Abstract: A method and circuit for initializing a buffer in a clock forwarded system. A buffer is configured for temporarily storing incoming data received on the clock-forwarded interface. The buffer may use a write pointer and a read pointer which may be clocked by two different clocks allowing independent write and read accesses to the buffer. In an initialization mode, a predetermined pattern of data may be written into an entry in the buffer. In one embodiment, a logic circuit may detect the predetermined pattern of data and may cause the value of the write pointer to be captured. A synchronizing circuit may synchronize an indication that the predetermined pattern of data has been detected to the clock used by the read pointer. The synchronizer circuit may then provide a initialize signal to the read pointer which stores the captured write pointer value into the read pointer.

Abstract: A computer system employs virtual channels and allocates different resources to the virtual channels. More particularly, the computer system provides a posted commands virtual channel separate from the non-posted commands virtual channel for routing posted and non-posted commands or requests through coherent and noncoherent fabrics within the computer system. Because separate resources are allocated to the virtual channels in the computer system, posted requests may be allowed to become unordered with other requests from the same source. Implementation of a separate posted commands virtual channel may allow the computer system to maintain compatibility with I/O systems in which posted write requests may become unordered with previous posted requests (e.g., the Peripheral Component Interconnect Bus, or PCI). Implementation of the separate posted commands virtual channel thus may assist in providing deadlock-free operation.

Abstract: An apparatus includes one or more interface circuits, an interconnect, a memory controller, a memory bridge, a packet DMA circuit, and a switch. The memory controller, the memory bridge, and the packet DMA circuit are coupled to the interconnect. Each interface circuit is coupled to a respective interface to receive packets and/or coherency commands from the interface. The switch is coupled to the interface circuits, the memory bridge, and the packet DMA circuit. The switch is configured to route the coherency commands from the interface circuits to the memory bridge and the packets from the interface circuits to the packet DMA circuit. The memory bridge is configured to initiate corresponding transactions on the interconnect in response to at least some of the coherency commands. The packet DMA circuit is configured to transmit write transactions on the interconnect to the memory controller to store the packets in memory.

Abstract: A computer system employs virtual channels and allocates different resources to the virtual channels. Packets which do not have logical/protocol-related conflicts are grouped into a virtual channel. Accordingly, logical conflicts occur between packets in separate virtual channels. The packets within a virtual channel may share resources (and hence experience resource conflicts), but the packets within different virtual channels may not share resources. Since packets which may experience resource conflicts do not experience logical conflicts, and since packets which may experience logical conflicts do not experience resource conflicts, deadlock-free operation may be achieved. Additionally, each virtual channel may be assigned control packet buffers and data packet buffers. Control packets may be substantially smaller in size, and may occur more frequently than data packets. By providing separate buffers, buffer space may be used efficiently.

Abstract: A high speed bus system for use in a shared memory system that allows for the high speed transmissions of commands and data between a number of processors and a memory array of a multi-processor, shared memory system, with the high speed bus system including a central unit and a series of uni-directional buses that connect between the plurality of processors and shared memory, with the central unit including arbitration logic and a series of multiplexers to determine which CPUs are granted access to shared buses, scheduling logic that works with the arbitration logic and multiplexers to determine which CPUs are granted access to the shared buses, and port logic for combining the CPU transmissions and determining if such transmissions are valid.

Abstract: A computer system employs virtual channels and allocates different resources to the virtual channels. Packets which do not have logical/protocol-related conflicts are grouped into a virtual channel. Accordingly, logical conflicts occur between packets in separate virtual channels. The packets within a virtual channel may share resources (and hence experience resource conflicts), but the packets within different virtual channels may not share resources. Since packets which may experience resource conflicts do not experience logical conflicts, and since packets which may experience logical conflicts do not experience resource conflicts, deadlock-free operation may be achieved. Additionally, nodes within the computer system may be configured to preallocate resources to process response packets. Some response packets may have logical conflicts with other response packets, and hence would normally not be allocable to the same virtual channel.

Abstract: A memory controller provides programmable flexibility, via one or more configuration registers, for the configuration of the memory. The memory may be optimized for a given application by programming the configuration registers. For example, in one embodiment, the portion of the address of a memory transaction used to select a storage location for access in response to the memory transaction may be programmable. In an implementation designed for DRAM, a first portion may be programmably selected to form the row address and a second portion may be programmable selected to form the column address. Additional embodiments may further include programmable selection of the portion of the address used to select a bank. Still further, interleave modes among memory sections assigned to different chip selects and among two or more channels to memory may be programmable, in some implementations.

Abstract: An adaptive retry mechanism may record latencies of recent transactions (e.g. the first data transfer latency), and may select a retry latency from two or more retry latencies. The retry latency may be used for a transaction, and may specify a point in time during the transaction at which the transaction is retried if the first data transfer has not yet occurred. In one implementation, the set of retry latencies includes a minimum retry latency, a nominal retry latency, and a maximum retry latency. The nominal retry latency may be set slightly greater than the expected latency of transactions in the system. The minimum retry latency may be less than the nominal retry latency and the maximum retry latency may be greater than the nominal retry latency. If latencies greater than the nominal retry latency but less than the maximum retry latency are being experienced, the maximum retry latency may be selected.

Abstract: A cache may be programmed to disable one or more entries from allocation for storing memory data (e.g. in response to a memory transaction which misses the cache). Furthermore, the cache may be programmed to select which entries of the cache are disabled from allocation. Since the disabled entries are not allocated to store memory data, the data stored in the entries at the time the cache is programmed to disable the entries may remain in the cache. In one specific implementation, the cache also provides for direct access to entries in response to direct access transactions.

Abstract: An apparatus includes one or more interface circuits, an interconnect, a memory controller, a memory bridge, a packet DMA circuit, and a switch. The memory controller, the memory bridge, and the packet DMA circuit are coupled to the interconnect. Each interface circuit is coupled to a respective interface to receive packets and/or coherency commands from the interface. The switch is coupled to the interface circuits, the memory bridge, and the packet DMA circuit. The switch is configured to route the coherency commands from the interface circuits to the memory bridge and the packets from the interface circuits to the packet DMA circuit. The memory bridge is configured to initiate corresponding transactions on the interconnect in response to at least some of the coherency commands. The packet DMA circuit is configured to transmit write transactions on the interconnect to the memory controller to store the packets in memory.

Abstract: A line predictor caches alignment information for instructions. In response to each fetch address, the line predictor provides alignment information for the instruction beginning at the fetch address, as well as one or more additional instructions subsequent to that instruction. The alignment information may be, for example, instruction pointers, each of which directly locates a corresponding instruction within a plurality of instruction bytes fetched in response to the fetch address. The line predictor may include a memory having multiple entries, each entry storing up to a predefined maximum number of instruction pointers and a fetch address corresponding to the instruction identified by a first one of the instruction pointers. Fetch addresses may be searched against the fetch addresses stored in the multiple entries, and if a match is detected the corresponding instruction pointers may be used.

Abstract: A computer system has a communication link that includes a control signal and data lines. A first control packet having a-plurality of bytes is transferred over the data lines from a first to a second node on the communication link. The control line is asserted to indicate transfer of a control packet. After transfer of the first control packet, a first portion of a multi-byte data packet associated with the first control packet is transferred with the control line deasserted. During transfer of the data packet the control line is asserted and transfer of the data packet is suspended. A second control packet is then transferred over the data lines. Subsequent to transferring the second control packet, the remainder of the data packet is transferred with the control line deasserted.

Abstract: An apparatus includes one or more interface circuits, an interconnect, a memory controller, a memory bridge, a packet DMA circuit, and a switch. The memory controller, the memory bridge, and the packet DMA circuit are coupled to the interconnect. Each interface circuit is coupled to a respective interface to receive packets and/or coherency commands from the interface. The switch is coupled to the interface circuits, the memory bridge, and the packet DMA circuit. The switch is configured to route the coherency commands from the interface circuits to the memory bridge and the packets from the interface circuits to the packet DMA circuit. The memory bridge is configured to initiate corresponding transactions on the interconnect in response to at least some of the coherency commands. The packet DMA circuit is configured to transmit write transactions on the interconnect to the memory controller to store the packets in memory.

Abstract: A method and system of expediting issuance of a second request of a pair of ordered requests into a distributed coherent communication fabric. The first request of the ordered pair is issued into the coherent communication fabric and directed to a first target. Issuance of the second request into the coherent communication fabric is stalled until the first target receives and orders the first request and transmits a response acknowledging the same.

Abstract: A messaging scheme that conserves system memory bandwidth during a memory read operation in a multiprocessing computer system is described. A source processing node sends a memory read command to a target processing node to read data from a designated memory location in a system memory associated with the target processing node. The target node transmits a read response to the source node containing the requested data and also concurrently transmits a probe command to one or more of the remaining nodes in the multiprocessing computer system. In response to the probe command each remaining processing node checks whether the processing node has a cached copy of the requested data. If a processing node, other than the source and the target nodes, finds a modified cached copy of the designated memory location, that processing node responds with a memory cancel response sent to the target node and a read response sent to the source node.

Abstract: A computer system is presented which implements a system and method for tracking the progress of posted write transactions. In one embodiment, the computer system includes a processing subsystem and an input/output (I/O) subsystem. The processing subsystem includes multiple processing nodes interconnected via coherent communication links. Each processing node may include a processor preferably executing software instructions. The I/O subsystem includes one or more I/O nodes. Each I/O node may embody one or more I/O functions (e.g., modem, sound card, etc.). The multiple processing nodes may include a first processing node and a second processing node, wherein the first processing node includes a host bridge, and wherein a memory is coupled to the second processing node. An I/O node may generate a non-coherent write transaction to store data within the second processing node's memory, wherein the non-coherent write transaction is a posted write transaction.

Abstract: A computer system is presented which implements a system and method for conveying packets between a coherent processing subsystem and a non-coherent input/output (I/O) subsystem. The processing subsystem includes a first processing node coupled to a second processing node via a coherent communication link. The first processing node includes a host bridge which translates packets moving between the processing subsystem and the I/O subsystem. The I/O subsystem includes an I/O node coupled to the first processing node via a non-coherent communication link. The I/O node may embody one or more I/O functions (e.g., modem, sound card, etc.). The coherent and non-coherent communication links are physically identical. For example, the coherent and non-coherent communication links may have the same electrical interface and the same signal definition. The host bridge translates non-coherent packets from the I/O node to coherent packets, and transmits the coherent packets to the second processing node.

Abstract: A processor includes execution resources for handling a first memory operation and a concurrent second memory operation. If one of the memory operations is misaligned, the processor may allocate the execution resources for the other memory operation to that memory operation. In one embodiment, the older memory operation proceeds if misalignment is detected. The younger memory operation is retried and may be reexecuted at a later time. If the older memory operation is misaligned, the execution resources provided for the younger operation may be allocated to the older memory operation. If only the younger memory operation is misaligned, the younger memory operation may be the older memory operation during a subsequent reexecution and may thus be allocated the execution resources to allow the memory operation to complete.