Sun Microsystems, Inc.

Meera Kasinathan

Ricky C Hetherington

Thomas M Wicki

Rajasekhar Cherabuddi

Kevin B Normoyle

Fong Pong

Anup K Sharma

Brian McGee

Sandeep A Aji

Sutikshan Bhutani

A multiple-way cache memory having a plurality of cache blocks and associated tag arrays includes a select circuit that stores way select values for each cache block. The way select values selectively disable one or more cache blocks from participating in cache operations by forcing tag comparisons associated with the disabled cache blocks to a mismatch condition so that the disabled cache blocks will not be selected to provide output data. The remaining enabled cache blocks may be operated as a less-associative cache memory without requiring cache addressing modifications.

Yield improvement through probe-based cache size reduction

A multiprocessor system includes a plurality of central processing units (CPUs) connected to one another by a system bus. Each CPU includes a cache controller to communicate with its cache, and a primary memory controller to communicate with its primary memory. When there is a cache miss in a CPU, the cache controller routes an address request for primary memory directly to the primary memory via the CPU as a speculative request without access the system bus, and also issues the address request to the system bus to facilitate data coherency. The speculative request is queued in the primary memory controller, which in turn retrieves speculative data from a specified primary memory address. The CPU monitors the system bus for a subsequent transaction that requests the specified data in the primary memory. If the subsequent transaction requesting the specified data is a read transaction that corresponds to the speculative address request, the speculative request is validated and becomes non-speculative. If, on the other hand, the subsequent transaction requesting the specified data is a write transaction, the speculative request is canceled.

Method to reduce memory latencies by performing two levels of speculation

The main cache of a processor in a multiprocessor computing system is coupled to receive writeback data during writeback operations. In one embodiment, during writeback operations, e.g., for a cache miss, dirty data in the main cache is merged with modified data from an associated write cache, and the resultant writeback data line is loaded into a writeback buffer. The writeback data is also written back into the main cache, and is maintained in the main cache until replaced by new data. Subsequent requests (i.e., snoops) for the data are then serviced from the main cache, rather than from the writeback buffer. In some embodiments, further modifications of the writeback data in the main cache are prevented. The writeback data line in the main cache remains valid until read data for the cache miss is returned, thereby ensuring that the read address reaches the system interface for proper bus ordering before the writeback line is lost. In one embodiment, the writeback operation is paired with the read operation for the cache miss to ensure that upon completion of the read operation, the writeback address has reached the system interface for bus ordering, thereby maintaining cache coherency while allowing requests to be serviced from the main cache.

Simplified writeback handling

A cache memory system having a cache and a cache tag. A cache tag cache is provided to store a subset of the most recently or frequently used cache tags. The cache tag cache is accessed during tag inquires in a manner similar to conventional cache tag inquires. Hits in the cache tag cache have a lower access latency than the tag lookups that miss and require access to the cache tag.

Cache tag caching

A cache memory system including a cache memory having a plurality of cache lines. An index portion of a tag array includes an n-bit pointer entry for every cache line. A shared tag portion of a tag array includes a number of entries, where each entry includes shared tag information that is shared among a plurality of the cache lines. Each n-bit pointer in the index portion of the tag array points into an entry in the shared tag portion.

Cache with reduced tag information storage

A cache system including a data cache memory comprising a plurality of cache lines. A tag store has an entry representing each line in the cache memory where each entry comprises tag information for accessing the data cache. The tag information includes state information indicating whether the represented cache line includes dirty data. A speculative write back unit monitors the state information and is operative to initiate a write back of a cache line having more than a preselected amount of dirty data.

Speculative cache line write backs to avoid hotspots

An automated method and system for detecting electromigration violations in signal lines of an integrated circuit design to be fabricated is disclosed. The automated method and system checks conductive traces, vias and/or contacts that are used to route signals to and from various functional cells within the integrated circuit design against predetermined process rules to detect electromigration violations. The operation and effectiveness of the automated method and system are far superior to conventional manual approaches.

Growing community of inventors

Sunnyvale, CA, United States of America

Meera Kasinathan