User`s guide

The XMI
2.5.1 Memory Block State
A memory block (a hexword) can be in one of the following states at any
given time:
1 Free, indicating that the memory block is neither OWNED nor
INTERLOCKED.
2 Interlocked, indicating that the memory block is INTERLOCKED as
a result of a successful IREAD transaction.
3 Owned, indicating that the memory block is OWNED by a writeback
cache within the system as a result of a successful OREAD transaction.
4 Tagged Bad Data, indicating that the data was corrupted in one
of the nodes and was written back to memory and tagged as a bad
location. This allows the error to be associated with a particular
process since it causes the next read-type transaction to this location
to fail. (Writes, because of their disconnected nature, do not permit an
association with a particular process.)
5 Unknown, indicating that the state bits associated with the memory
block contain an uncorrectable error, and therefore the actual state
cannot be determined.
Table 2–15 shows the memory responses to various XMI transactions given
the state of the memory block.
Table 2–15 Memory Response
Command Free Interlocked Owned
Tagged
Bad Data Unknown
READ GRD GRD GRD RER RER
IREAD GRD (Interlocked)
1
LOC LOC RER RER
OREAD GRD (Owned)
1
LOC LOC RER RER
WMASK Write Write Write Write Write
UWMASK Write
2
Write (Free)
1
Write
2
Write
2
Write
DWMASK Write (Free)
2
N/A Write (Free)
1
Write
2
Write
TBDATA Write (Tagged Bad)
2
Write (Tagged Bad)
2
Write (Tagged Bad)
1
Write
2
Write
1
The "next state," when it is different from the current state.
2
The "next state," when it is different from the current state. This "next state" represents an error condition.
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