User`s guide

The XMI
2.1.4 XMI Terms
The following terms are used to describe XMI transactions:
Term Definition
Node A hardware device that connects to the XMI backplane.
Transfer The smallest quantum of work that occurs on the XMI. An example of a transfer is the
command cycle of a read. Another example is the command cycle for a write, followed by
data cycles.
Cycle The complete execution of one XMI clock time period.
Transaction The logical task being performed (such as a read). A transaction is composed of one or
more transfers. As an example of a transaction, the read consists of a command transfer
followed, some time later, by a return data transfer.
Commander The node that initiated the transaction in progress. For example, the commander initiates
a read transaction while the responder (data source) initiates the read data transfer. The
responder is not the commander for the read data transfer because the transfer was
requested by the commander node.
Responder The node that responds to the commander in a transaction.
Transmitter The node that is sourcing the information on the bus. For example, during a read transaction
the commander is the transmitter during the command transfer but is the receiver during the
return data transfer.
Receiver The node that is the target during a transfer.
Naturally aligned Describes a data quantity whose address could be specified as an offset, from the beginning
of memory, of an integral number of data elements of the same size. The lower bits of a
naturally aligned data item are zero. All XMI writes transfer a naturally aligned block of data.
Wraparound read An octaword or hexword read where read data is returned with the specifically addressed
quadword first, independent of alignment. The remaining data in the naturally aligned
block of data containing the addressed quadword is returned in subsequent transfers. See
Section 2.1.5.
Byte A single 8-bit entity.
63 56 55 48 47 40 39 32 31 24 23 16 15 8 7 0
byte7 byte6 byte5 byte4 byte3 byte2 byte1 byte0
msb−p156−89
Word A single 16-bit entity.
63 48 47 32 31 16 15 0
word 3 word 2 word 1 word 0
msb−p157−89
2–7