Method and apparatus for duplicating tag systems to maintain add

Details Method and apparatus for duplicating tag systems to maintain add Method and apparatus for duplicating tag systems to maintain add

1997-01-17

1999-11-02

Gossage, Glenn

Electrical computers and digital processing systems: memory

Storage accessing and control

Hierarchical memories

711141, 711146, 711144, G06F 1300, G06F 1212

Patent

active

059788860

ABSTRACT:
An apparatus and method for duplicating tag addresses to maintain addresses of central processing unit (CPU) data stored in write buffers external to a cache are disclosed. Advance notification of write transactions is issued to allow a subsystem that maintains duplicate cache tags to know in advance which write transactions are present in the CPU's buffers. Such information is used to keep duplicate tags for both the cache and any buffers that contain writes that are to be removed from the cache. The cache is preferably a direct mapped cache and the CPU preferably resides within a multiprocessor architecture. In the preferred embodiment, all write transactions are indirectly caused by a read transaction that is about to bring a line into the cache. Thus, a read transaction is issued by the CPU before the write transaction is issued. A field is added to the read transaction that indicates whether or not the read transaction has a corresponding line that must be written out of the cache and into a buffer, such that the duplicate tags duplicate both the CPU cache and the CPU write buffers.

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