User`s guide

The XMI
2.4.2.3 Length Field
The Length field is XMI D<31:30> L. The Length field is used to define
the number of words in the XMI data transfer. Table 2–11 shows the
Length field coding. Longword-length transactions are only used in
I/O space. Quadword-, octaword-, and hexword-length transactions are
only used in memory space. Hexword lengths are used for Read, Write,
Ownership Read, Disown Write Mask, Tag Bad Data, and Interlock Read
transactions.
Table 2–11 XMI Transaction Length Codes
XMI
D<31:30> L
Logic Levels
31 30 Size
0 0 Hexword
0 1 Longword
1 0 Quadword
1 1 Octaword
2.4.2.4 Address Field
The Address fields, XMI D<57:48> and XMI D<29:0> L, define the address
of an XMI read or write transaction. If the address of the transaction is
expressed as a 32-bit quantity, then:
• A<31> = D<32>
• A<30:29> = D<49:48>
• A<28:0> = D<28:0>
The number of significant bits in the address depends on the transaction
type and length, as shown in Figure 2–10.
Quadword, octaword, and hexword write transactions are assumed to be
naturally aligned, allowing the lower bits of the address to be "don’t care."
Reads require that the lower bits be significant because memory does
wraparound reads. All wrapped reads need to identify the quadword to be
transferred first.
For longword-length read transactions, A<1:0> are only significant for a
VAXBI word-mode or byte-mode transaction in I/O space. A<1> is required
for word mode, and A<1:0> are required for byte mode.
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