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Memory system messages come in four basic varieties, as
conveyed by the s.type field:
- REQUEST
- Sent by a processor or cache to
request some action related to the data requirements of the processor;
may demand a data transfer.
- REPLY
- Sent by a cache or directory
in response to the demands of a REQUEST; may include
a data transfer.
- COHE
- Sent by a directory to other caches with
a demand to invalidate or change the state of a line; may demand
a data transfer.
- COHE_REPLY
- Sent by a cache in response to the demands
of a COHE, or a replacement message; may include a data
transfer.
Each of these four basic categories is further divided according to
the req_type field and, in some cases, the s.reply and
s.nack_st fields. These fields are described in the following
sections.
Vijay Sadananda Pai
Thu Aug 7 14:18:56 CDT 1997