Advanced Computer Architecture Chapter 7.28
Remote
Read
Place Data
on Bus?
Snoop Cache Extensions
•Extensions:
Fourth State: Ownership
Remote
 Write
or  Miss due to
address conflict
Write back block
Remote Write or
Miss due to
address conflict
Invalid
Shared
(read/only)
Modified
(read/write)
CPU Read hit
CPU Read
CPU Write
Place Write
Miss on bus
CPU Write
CPU read hit
CPU write hit
Exclusive (read/only)
CPU Write
Place Write
Miss on Bus?
CPU Read hit
Remote Read
Write back
block
Shared-> Modified,
need invalidate only (upgrade request), don’t read memory
Berkeley Protocol
Clean exclusive state (no miss for private data on write)
MESI Protocol
Cache supplies data when shared state
(no memory access)
Illinois Protocol
 Place read miss
     on bus
Place Write
Miss on
Bus