Abstract: A method of extending a cache of a processing unit in a multi-processor computer system, by expanding the prior-art MESI cache-coherency protocol to include an additional cache-entry state corresponding to a most recently accessed state. A value is loaded from system memory into one or more caches of adjacent processing units, and when a requesting processing unit issues an inquiry onto the system bus to read the value, the value is sourced from the cache of the adjacent processing unit containing a copy of the value that was most recently accessed. Each cache has at least one cache line with a block for storing the value, and an indication is provided that a cache line having a block which contains an instruction or data is in a “recently read” state. Each cache entry has three bits to indicate the current state of the cache entry (one of five possible states).

Abstract: The present invention is a method and apparatus for preventing the occurrence of deadlocks from the execution of multiply-initiated multiply-sourced variable delay system bus operations. In general, each snooper excepts a given operation at the same time according to an agreed upon condition. In other words, the snooper in a given cache can accept an operation and begin working on it even while retrying the operation. Furthermore, none of the active snoopers release an operation until all the active snoopers are done with the operation. In other words, execution of a given operation is started by the snoopers at the same time and finished by each of the snoopers at the same time. This prevents the ping-pong deadlock by keeping any one cache from finishing the operation before any of the others.

Abstract: A queued arbitration mechanism transfers all queued processor bus requests to a centralized system controller/arbiter in a descriptive and pipelined manner. Transferring these descriptive and pipelined bus requests to the system controller allows the system controller to optimize the system bus utilization via prioritization of all of the requested bus operations and pipelining appropriate bus grants. Intelligent bus request information is transferred to the system controller via encoding and serialization techniques.

Abstract: An information handling system which efficiently processes auxiliary functions such as graphics processing includes one or more processors, a high speed processor bus connecting the one or more processors, a memory controller for controlling memory and for controlling the auxiliary function processing, a memory system, and an I/O bus having one or more I/O controllers with I/O devices connected thereto.

Abstract: A method and apparatus for preventing the occurrence of deadlocks from the execution of variable delay system bus operations. In general, each snooper excepts a given operation at the same time according to an agreed upon condition. In other words, the snooper in a given cache can accept an operation and begin working on it even while retrying the operation. Furthermore, none of the active snoopers release an operation until all the active snoopers are done with the operation. Execution of a given operation is started by the snoopers at the same time and finished by each of the snoopers at the same time. This prevents the ping-pong deadlock by keeping any one cache from finishing the operation before any of the others. The snoopers initiate operations at the same time based upon a common predefined event and ensure the operations end are finished concurrently when no outstanding retry operations are detected.

Abstract: A method and apparatus for preventing the occurrence of deadlocks from the execution of unresolvable system bus operations. In general, each snooper speculatively accepts a given operation when it has a snoop buffer available. However, rather than unconditionally processing the operation, the snooper waits to determine if another participant retried the operation due to unavailability of a snoop buffer. If some snooping participant retrys an operation, all snoopers that speculatively accepted an operation for processing abandon said operation. If no snooping participant retrys the operation, sufficient snooping resources were available for all necessary caches to begin processing the operation and the initiator can consider the operation completed. In other words, no operation is processed until all the necessary snooping resources are available to accept the operation. This prevents the system from getting into the ping-pong deadlock.

Abstract: The present invention is a method and apparatus for preventing the occurrence of deadlocks from the execution of singly-initiated singly-sourced variable delay system bus operations. In general, each snooper excepts a given operation at the same time according to an agreed upon condition. In other words, the snooper in a given cache can accept an operation and begin working on it even while retrying the operation. Furthermore, none of the active snoopers release an operation until all the active snoopers are done with the operation. In other words, execution of a given operation is started by the snoopers at the same time and finished by each of the snoopers at the same time. This prevents the ping-pong deadlock by keeping any one cache from finishing the operation before any of the others.

Abstract: A method and apparatus for preventing the occurrence of deadlocks from the execution of unresolvable system bus operations. In general, each snooper speculatively accepts a given operation when it has a snoop buffer available. However, rather than unconditionally processing the operation, the snooper waits to determine if another participant retried the operation due to unavailability of a snoop buffer. If some snooping participant retrys an operation, all snoopers that speculatively accepted an operation for processing abandon said operation. If no snooping participant retrys the operation, sufficient snooping resources were available for all necessary caches to begin processing the operation and the initiator can consider the operation completed. In other words, no operation is processed until all the necessary snooping resources are available to accept the operation. This prevents the system from getting into the ping-pong deadlock.

Abstract: A method and apparatus for preventing the occurrence of deadlocks from the execution of multiply-initiated multiply-sourced variable delay system bus operations. In general, each snooper excepts a given operation at the same time according to an agreed upon condition. In other words, the snooper in a given cache can accept an operation and begin working on it even while retrying the operation. Furthermore, none of the active snoopers release an operation until all the active snoopers are done with the operation. In other words, execution of a given operation is started by the snoopers at the same time and finished by each of the snoopers at the same time. This prevents the ping-pong deadlock by keeping any one cache from finishing the operation before any of the others.

Abstract: An information handling system includes one or more processing units, a data management unit, connected to the processor data bus, to a memory system, and to an I/O bus, an address management unit, connected to the processor address bus, to the memory system, and to an I/O bus. Data management unit also includes interrupt routing logic which snoops interrupt packets, stores the information in registers, and generates a signal indicating whether a particular interrupt was accepted or rejected. If the interrupt logic has a higher priority interrupt pending, the current interrupt packet will be returned to the requesting device using the interrupt return transaction, and the requesting device will accept the return transaction by decoding the bus unit ID field in the packet. The interrupt will be requeued and held in a pending status until an interrupt reissue transaction is transmitted by the interrupt routing logic and received by the interrupting I/O controller.

Abstract: In multi-processor systems which have separated the system bus from the I/O bus, a Shadow Directory is introduced into the memory controller for reducing bottlenecks that occur from the processors snooping data cache in the I/O devices residing on the I/O bus. This Shadow Directory is advantageously employed in a system, such as the PowerPc architecture which distinguishes between the types of data that can be cached in I/O devices. The Shadow Directory uses two First In First Out (FIFO) stacks for two different types of data. These FIFO stacks are then used for addresses placed on the system bus and I/O bus in order to reduce snoop latency times.

Abstract: A queued arbitration mechanism transfers all queued processor bus requests to a centralized system controller/arbiter in a descriptive and pipelined manner. Transferring these descriptive and pipelined bus requests to the system controller allows the system controller to optimize the system bus utilization via prioritization of all of the requested bus operations and pipelining appropriate bus grants. Intelligent bus request information is transferred to the system controller via encoding and serialization techniques.

Abstract: A method of providing instructions and data values to a processing unit in a multi-processor computer system, by expanding the prior-art MESI cache-coherency protocol to include an additional cache-entry state corresponding to a most recently accessed state. Each cache of the processing units has at least one cache line with a block for storing the instruction or data value, and an indication is provided that a cache line having a block which contains the instruction or data value is in a "recently read" state. Each cache entry has three bits to indicate the current state of the cache entry (one of five possible states). A processing unit which desires to access a shared instruction or data value detects transmission of the indication from the cache having the most recently accessed copy, and the instruction or data value is sourced from this cache.

Abstract: A method of improving memory latency associated with a read-type operation in a multiprocessor computer system is disclosed. After a value (data or instruction) is loaded from system memory into a cache, the cache is marked as containing an exclusively held, unmodified copy of the value and, when a requesting processing unit issues a message indicating that it desires to read the value, and the cache transmits a response indicating that the cache can source the value. The response is transmitted in response to the cache snooping the message from an interconnect which is connected to the requesting processing unit. The response is detected by system logic and forwarded from the system logic to the requesting processing unit. The cache then sources the value to an interconnect which is connected to the requesting processing unit. The system memory detects the message and would normally source the value, but the response informs the memory device that the value is to be sourced by the cache instead.

Abstract: A shift register is used to latch the bus-driver-enable signal for each potential bus driver during each system clock cycle. The shift register clock will freeze upon receipt of a "check stop" signal. Once frozen, the shift register can be scanned for fault isolation analysis.

Abstract: A method of improving memory latency associated with a read-type operation in a multiprocessor computer system is disclosed. After a value (data or instruction) is loaded from system memory into a plurality of caches, one cache is identified as a specific cache which contains an unmodified copy of the value that was most recently read, and that cache is marked as containing the most recently read copy, while the remaining caches are marked as containing shared, unmodified copies of the value. When a requesting processing unit issues a message indicating that it desires to read the value, the specific cache transmits a response indicating that it cache can source the value. The response is transmitted in response to the cache snooping the message from an interconnect which is connected to the requesting processing unit. The response is detected by system logic and forwarded from the system logic to the requesting processing unit.

Abstract: A method of improving memory latency associated with a read-type operation in a multiprocessor computer system is disclosed. A requesting processing unit issues a message to an interconnect of the computer system indicating that the requesting processing unit desires to read a value from an address of a memory device of the computer system, and each cache snoops the interconnect to detect the message.

Abstract: A method of improving memory latency associated with a read-type operation in a multiprocessor computer system is disclosed. After a value (data or instruction) is loaded from system memory into at least two caches, the caches are marked as containing shared, unmodified copies of the value and, when a requesting processing unit issues a message indicating that it desires to read the value, a given one of the caches transmits a response indicating that the given cache can source the value. The response is transmitted in response to the cache snooping the message from an interconnect which is connected to the requesting processing unit. The response is detected by system logic and forwarded from the system logic to the requesting processing unit. The cache then sources the value to an interconnect which is connected to the requesting processing unit.

Abstract: A method of reducing memory latency associated with a read-type operation in a multiprocessor computer system is disclosed. When a requesting processing unit issues a message indicating that it desires to read a value from an address of a memory device of the computer system, each cache snoops an interconnect to detect the message, and transmits a response to the message, wherein a shared intervention response is transmitted to indicate that a cache containing an unmodified value corresponding to the address of the memory device can source the value. A priority is associated with each response, and system logic detects each response and its associated priority, and forwards a response with a highest priority to the requesting processing unit. The protocol may include prior-art coherency responses such as an invalid response, a modified intervention response, a shared response, and a retry response. Either the retry response or the shared intervention response may be assigned a highest priority.

Abstract: To present a consistent image of storage facilities to components in Bi-modal Endian PowerPC system enviromnents, provision is made for transferring data between system components in the appropriate Endian format. Endian conversion function can be incorporated into the memory controller subsystem by adding byte-lane swapping logic on the inbound and outbound I/O data paths. With this structure, inbound data from the processor and memory bus will be converted to true Little Endian order before being sent to I/O devices. Likewise, true Little Endian data from I/O devices targeted for the processor or memory is modified to reflect the PowerPC Little Endian byte ordering convention.