User`s guide

The XMI
2.5.4 Ownership Read Transaction
The Ownership Read (OREAD) transaction (see Figure 2–15) is used with
the Disown Write Mask transaction for the block ownership writeback
protocol.
Figure 2–15 Ownership Read Command
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90
DON’T CARE ADDRESS<29:0>
LENGTH 00 = Hexword
msb−p188−89
0011 MBX
ADDRESS<39:30>
OWNERSHIP READ COMMAND
A writeback cache node issues an OREAD to a hexword memory
block whenever it has a cache miss for a location that is likely to
be subsequently written, either because the processor was actually
performing a write to the location or was performing a read with the
"modify intent flag" signal asserted. The memory node’s response to an
OREAD depends on the state of the ownership and interlock bits. The
XMI supports only hexword OREAD transactions. Nodes that work with
a vector module issue a two-cycle OREAD by following the OREAD with
a null cycle because the vector module cannot process invalidates in one
XMI cycle.
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