Abstract: A processing unit for a multiprocessor data processing system includes a processor core and a cache hierarchy coupled to the processor core to provide low latency data access. The cache hierarchy includes an upper level cache coupled to the processor core and a lower level victim cache coupled to the upper level cache. In response to a prefetch request of the processor core that misses in the upper level cache, the lower level victim cache determines whether the prefetch request misses in the directory of the lower level victim cache and, if so, allocates a state machine in the lower level victim cache that services the prefetch request by issuing the prefetch request to at least one other processing unit of the multiprocessor data processing system.

Abstract: A cache, system and method for improving the snoop bandwidth of a cache directory. A cache directory may be sliced into two smaller cache directories each with its own snooping logic. By having two cache directories that can be accessed simultaneously, the bandwidth can be essentially doubled. Furthermore, a “frequency matcher” may shift the cycle speed to a lower speed upon receiving snoop addresses from the interconnect thereby slowing down the rate at which requests are transmitted to the dispatch pipelines. Each dispatch pipeline is coupled to a sliced cache directory and is configured to search the cache directory to determine if data at the received addresses is stored in the cache memory. As a result of slowing down the rate at which requests are transmitted to the dispatch pipelines and accessing the two sliced cache directories simultaneously, the bandwidth or throughput of the cache directory may be improved.

Abstract: A processing unit for a data processing system includes a processor core having one or more execution units for processing instructions and a register file for storing data accessed in processing of the instructions. The processing unit also includes a multi-level cache hierarchy coupled to and supporting the processor core. The multi-level cache hierarchy includes at least one upper level of cache memory having a lower access latency and at least one lower level of cache memory having a higher access latency. The lower level of cache memory, responsive to receipt of a memory access request that hits only a partial cache line in the lower level cache memory, sources the partial cache line to the at least one upper level cache memory to service the memory access request. The at least one upper level cache memory services the memory access request without caching the partial cache line.

Abstract: In response to a memory access request of a processor core that targets a target cache line, the lower level cache of a vertical cache hierarchy associated with the processor core supplies a copy of the target cache line to an upper level cache in the vertical cache hierarchy and retains a copy in a shared coherence state. The upper level cache holds the copy of the target cache line in a private shared ownership coherence state indicating that each cached copy of the target memory block is cached within the vertical cache hierarchy associated with the processor core. In response to the upper level cache signaling replacement of the copy of the target cache line in the private shared ownership coherence state, the lower level cache updates its copy of the target cache line to the exclusive ownership coherence state without coherency messaging with other vertical cache hierarchies.

Abstract: An LBIST captures pseudo-random values from a pseudo-random pattern generator. Next, the LBIST stabilizes an untimed logic path by inputting the captured pseudo-random value into the untimed logic path. In turn, the LBIST tests one or more timed signal transitions that are dependent upon the stabilized untimed logic path.

Abstract: A processing unit includes a processor core and a cache memory coupled to the processor core. The cache memory includes a data array, a directory of the data array, error detection logic that sequentially detects a first, second and third correctable errors in the data array of the cache memory and provides indications of detection of the first, second and third correctable errors, and control circuitry that, responsive to the indication of the third correctable error and an indication that the first and second correctable errors occurred at too high a frequency, marks an entry of the data array containing a cache line having the third correctable error as deleted in the directory of the cache memory regardless of which entry of the data array contains a cache line having the second correctable error.

Abstract: A processing unit for a data processing system includes a processor core having one or more execution units for processing instructions and a register file for storing data accessed in processing of the instructions. The processing unit also includes a multi-level cache hierarchy coupled to and supporting the processor core. The multi-level cache hierarchy includes at least one upper level of cache memory having a lower access latency and at least one lower level of cache memory having a higher access latency. The lower level of cache memory, responsive to receipt of a memory access request that hits only a partial cache line in the lower level cache memory, sources the partial cache line to the at least one upper level cache memory to service the memory access request. The at least one upper level cache memory services the memory access request without caching the partial cache line.

Abstract: In response to a data request, a victim cache line is selected for castout from a lower level cache, and a target lower level cache of one of the plurality of processing units is selected. A determination is made whether the selected target lower level cache has provided more than a threshold number of retry responses to lateral castout (LCO) commands of the first lower level cache, and if so, a different target lower level cache is selected. The first processing unit thereafter issues a LCO command on the interconnect fabric. The LCO command identifies the victim cache line to be castout and indicates that the target lower level cache is an intended destination of the victim cache line. In response to a successful coherence response to the LCO command, the victim cache line is removed from the first lower level cache and held in the second lower level cache.

Abstract: In response to a data request of a first processing unit among a plurality of processing units, the first processing unit selects a victim cache line to be castout from the lower level cache of the first processing unit and selects the lower level cache of a second of the plurality of processing units as an intended destination of a lateral castout (LCO) command by randomized round-robin selection. The first processing unit issues on the interconnect fabric an LCO command identifying the victim cache line and the intended destination. In response to a coherence response to the LCO command indicating success of the LCO command, the first processing unit removes the victim cache line from its lower level cache, and the victim cache line is held in the lower level cache of one of the plurality of processing units other than the first processing unit.

Abstract: In response to a data request of a first of a plurality of processing units, the first processing unit selects a victim cache line to be castout from the lower level cache of the first processing unit and determines whether a mode is set. If not, the first processing unit issues on the interconnect fabric an LCO command identifying the victim cache line and indicating that a lower level cache is the intended destination. If the mode is set, the first processing unit issues a castout command with an alternative intended destination. In response to a coherence response to the LCO command indicating success of the LCO command, the first processing unit removes the victim cache line from its lower level cache, and the victim cache line is held elsewhere in the data processing system. The mode can be set to inhibit castouts to system memory, for example, for testing.

Abstract: A victim cache line having a data-invalid coherence state is selected for castout from a first lower level cache of a first processing unit. The first processing unit issues on an interconnect fabric a lateral castout (LCO) command identifying the victim cache line to be castout from the first lower level cache, indicating the data-invalid coherence state, and indicating that a lower level cache is an intended destination of the victim cache line. In response to a coherence response to the LCO command indicating success of the LCO command, the victim cache line is removed from the first lower level cache and held in a second lower level cache of a second processing unit in the data-invalid coherence state.

Abstract: A victim cache memory includes a cache array, a cache directory of contents of the cache array, and a cache controller that controls operation of the victim cache memory. The cache controller, responsive to receiving a castout command identifying a victim cache line castout from another cache memory, causes the victim cache line to be held in the cache array. If the other cache memory is a higher level cache in the cache hierarchy of the processor core, the cache controller marks the victim cache line in the cache directory so that it is less likely to be evicted by a replacement policy of the victim cache, and otherwise, marks the victim cache line in the cache directory so that it is more likely to be evicted by the replacement policy of the victim cache.

Abstract: A data processing system includes a first processing unit and a second processing unit coupled by an interconnect fabric. The first processing unit has a first processor core and associated first upper and first lower level caches, and the second processing unit has a second processor core and associated second upper and lower level caches. In response to a data request, a victim cache line is selected for castout from the first lower level cache. The first processing unit issues on the interconnect fabric a lateral castout (LCO) command that identifies the victim cache line to be castout from the first lower level cache and indicates that a lower level cache is an intended destination. In response to a coherence response indicating success of the LCO command, the victim cache line is removed from the first lower level cache and held in the second lower level cache.

Abstract: An LBIST captures pseudo-random values from a pseudo-random pattern generator. Next, the LBIST stabilizes an untimed logic path by inputting the captured pseudo-random value into the untimed logic path. In turn, the LBIST tests one or more timed signal transitions that are dependent upon the stabilized untimed logic path.

Abstract: A data processing system includes a processor core having an associated upper level cache and a lower level victim cache. In response to a memory access request of the processor core, the lower level cache victim determines whether the memory access request hits or misses in the directory of the lower level victim cache, and the upper level cache determines whether a castout from the upper level cache is to be performed and selects a victim coherency granule for eviction from the upper level cache. In response to determining that a castout from the upper level cache is to be performed, the upper level cache evicts the selected victim coherency granule. In the eviction, the upper level cache reads out the victim coherency granule from the data array of the upper level cache only in response to an indication that the memory access request misses in the directory of the lower level victim cache.

Abstract: A method and computer system for reducing the wiring congestion, required real estate, and access latency in a cache subsystem with a sectored and sliced lower cache by re-configuring sector-to-slice allocation and the lower cache addressing scheme. With this allocation, sectors having discontiguous addresses are placed within the same slice, and a reduced-wiring scheme is possible between two levels of lower caches based on this re-assignment of the addressable sectors within the cache slices. Additionally, the lower cache effective address tag is re-configured such that the address fields previously allocated to identifying the sector and the slice are switched relative to each other's location within the address tag. This re-allocation of the address bits enables direct slice addressing based on the indicated sector.

Abstract: A cache coherent data processing system includes a memory and at least first and second coherency domains that each include a respective one of first and second cache memories. A master in the first coherency domain selects a scope of an initial broadcast of an operation targeting a request address allocated to the memory from among a first scope including only the first coherency domain and a second scope including both the first and second coherency domains. The master selects the scope based, at least in part, upon whether the memory belongs to the first coherency domain and performs an initial broadcast of the operation within the cache coherent data processing system utilizing the selected scope.

Abstract: A multiprocessor data processing system includes at least first and second coherency domains, where the first coherency domain includes a system memory and a cache memory. According to a method of data processing, a cache line is buffered in a data array of the cache memory and a state field in a cache directory of the cache memory is set to a coherency state to indicate that the cache line is valid in the data array, that the cache line is held in the cache memory non-exclusively, and that another cache in said second coherency domain may hold a copy of the cache line.

Abstract: Private devices are implemented on the secondary interface of PCI bridge by re-routing the activation of device select signals (IDSEL) during the address phase of a Type 0 configuration operation on the secondary bus in response to a Type 1 configuration operation on its primary bus. Under control of a mask register and device select reroute circuit, if a configuration command on the primary interface attempts to activate the IDSEL line associated with one of the private, or reroute, devices on the secondary interface, a different IDSEL is activated to select a monitoring device on the secondary interface.

Abstract: To prevent data performance impacts when dealing with target devices that can only transfer data for a limited number of bytes before disconnecting, the invention implements a short term data cache on the bridge. Using this feature, the bridge will cache additional data beyond a predetermined quantity of data following a disconnect with the requesting device. As such, the bridge may continue to prefetch additional data up to an amount specified by a prefetch read byte count and return the additional data should the requesting device request additional data resuming at the point of disconnect. However, the bridge will discard the additional data when at least one of the following occurs: a) the requesting device disconnects data transfer, and b) a further READ request that resumes at the point of disconnect is not received within a predetermined time.