User`s guide

The XMI
2.4.5 Locked Response Cycle (LOC)
The Locked Response indicates that the location specified in an Interlock
Read or Ownership Read transaction is not accessible at this time. Such a
location is either owned by another node or involved in an interlock pair of
transactions. Therefore, the LOC response is given by memory for one of
the following reasons:
• The command is an IREAD and the location is currently locked by
another node.
• The command is either an IREAD or an OREAD and the location is
within a hexword block currently owned by another node.
• The command is an OREAD and the location is either owned by
another node or is interlocked by another node.
During this cycle the responder drives 0100 on XMI F<3:0> L and the
commander’s ID on XMI ID<5:0> L. The value of the data bits, D<63:0> L,
is unspecified but must be consistent with P<2:0> L. A Locked Response
signals the termination of either an Interlock Read or Ownership Read
transaction. When issued, it is always the first and only read response
to the transaction. Nodes always reattempt a transaction that receives a
LOC response until timeout.
2.4.6 Read Error Response Cycle (RER)
The Read Error Response indicates that a Read, Interlock Read,
Ownership Read, or IDENT transaction completed unsuccessfully due
to an error condition at the responder node. The Read Error Response is
used for an uncorrectable memory error or a reference to a nonexistent
location on the VAXBI. During this cycle the responder drives 0101 on
XMI F<3:0> L and the commander’s ID on XMI ID<5:0> L. The value
of the data bits, D<63:0> L, is unspecified but must be consistent with
XMI P<2:0> L. A Read Error Response signals the termination of the
transaction, and no further read responses are provided.
2.4.7 The Null Cycle
A null cycle is an unused XMI cycle as no node has requested the bus. The
null cycle is ignored by all XMI responders.
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