User`s guide

The XMI
2.1.5 Wraparound Reads
Read data is returned in a specific pattern referred to as "wraparound
read" for octaword or hexword read operations. In a wraparound read,
the specifically addressed quadword is returned first, independent of
alignment. The remaining data in the naturally aligned block of data
containing the addressed quadword is returned in subsequent transfers.
A naturally aligned octaword is pointed to by an address that ends in 0,
10, 20, 30, and so forth. A naturally aligned hexword is pointed to by an
address that ends in 0, 20, 40, 60, and so forth.
XMI protocol requires that all octaword and hexword reads, both normal
and interlocked, be treated as wraparound reads.
2.1.5.1 Octaword Wraparound Read
The following is an example of an octaword wraparound read at VAX byte
address 00000018 (hex):
Notice that the natural octaword boundary is addressed by 00000010, but
the first quadword returned is that addressed by 00000018.
2.1.5.2 Hexword Wraparound Read
A hexword read is decomposed into two octaword reads, with the
addressed octaword read data returned first. Within each of the octawords,
the wrapping order is the same as described for the octaword. Return data
for the second octaword maintains the same wrapping order used in the
first octaword.
The following is an example of a hexword wraparound read at VAX byte
address 00000018 (hex):
The following is an example of a hexword wraparound read at VAX byte
address 00000074 (hex):
In this case the addressed byte is located in the first quadword of the
second octaword of the naturally aligned hexword pointed to by address
00000060 (hex).
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