Appeal No. 2001-2164
Application No. 09/024,620
with system memory. One and only one of these shared-modified
cache lines is uniquely identified to enable intervention (i.e.,
a process whereby a cache can source a requested value in lieu of
the system memory sourcing the value) using the uniquely
identified cache line. The identification is accomplished by
expanding the prior art MESI cache coherency protocol to include
a new cache coherency state, the “tagged” state.
This “tagged” state indicates:
1. That the value contained in the “tagged” cache-line is
shared, i.e., the same value is also present in the
horizontally-oriented cache lines of other processing units.
2. That the value in the “tagged” cache line is in a
modified state, i.e., the value is not consistent with
system memory, so that if the value is to be supplied to any
other processing units, it must come from one of the cache
lines sharing the value, and not from system memory.
3. That the specific “tagged” cache in this “tagged” cache
coherency state will be responsible for intervening the
value, as well as writing the value, to system memory
should a flush of the value from that particular cache
occur.
The instant claims are directed to a particular
implementation of the T-MESI cache coherency protocol in which
different priorities are associated with cache coherency
responses, including the tagged intervention response.
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