Glossary

acknowledge:

An acknowledge packet.

acknowledge gap:

The period of idle bus between the end of a packet and the start of an acknowledge.

acknowledge packet:

A linklayer packet returned by a destination node back to a source node in response to most primary packets. An acknowledge is always exactly 8 bits long.

application environment:

The physical environment of a backplane serial bus. This includes the bus itself, the modules, and the system that contains them. This environment may be a standardized host backplane (e.g., a Futurebus+ profile) that describes signal requirements, transceivers, mechanical arrangement of the modules, and temperature range over which operation is guaranteed.

arbitration:

The process by which nodes compete for ownership of the bus. The cable environment uses a hierarchical pointtopoint algorithm, while the backplane environment uses the bitserial process of transmitting an arbitration sequence. At the completion of an arbitration contest only one node will be able to transmit a data packet.

arbitration clock rate:

The rate used to define a number of timing requirements within the backplane physical layer. It is 49.152 MHz ± 100 ppm, regardless of the backplane interface technology.

arbitration reset gap:

The minimum period of idle bus time that must occur after a source using the fairness protocol has won an arbitration contest before it can once again compete for bus mastership. This is longer than a normal subaction gap.

arbitration sequence:

For the backplane environment, a set of bits transmitted by nodes that wish to transmit packets that is used to determine which will be able to transmit next.

arbitration signal:

Bidirectional signal exchanged between nodes during arbitration one of the PDUs for the physical layer (the other is the data bit).

asynchronous packet:

A primary packet that contains the bus_ID of the destination in the first quadlet, and is sent as the request subaction and/or response subaction of a transaction.

attached peer PHY:

Peer cable PHY at the other end of a particular physical connection from the local PHY.

backplane physical layer:

The version of the physical layer applicable to the Serial Bus backplane environment.

backplane PHY:

Abbreviation for the backplane physical layer.

base rate:

The lowest data rate used by the Serial Bus in a particular cable environment. In multiple speed environments, all nodes must be able to receive and transmit at the base rate. The base rate for the cable environment is98.304 MHz ± 100 ppm.

broadcast_physical_ID:

A physical_ID with a value of 1111112.

bus_ID:

A 10bit number uniquely specifying a particular bus within a system of multiple interconnected buses.

bus manager:

The node that provides advanced power management, optimizes Serial Bus performance, describes the topology of the bus, and crossreferences the maximum speed for data transmission between any two nodes on the bus. The bus manager node may also be the isochronous resource manager node.

byte:

Eight bits of data.

cable physical layer:

The version of the physical layer applicable to the Serial Bus cable environment.

cable PHY:

Abbreviation for the cable physical layer.

concatenated transaction:

A transaction in which the request and response subactions are directly concatenated without a gap between the acknowledge of the request and the response packet.

connected PHY:

Peer cable PHY at the other end of a particular physical connection from the local PHY.

CSR Architecture:

Refers to ISO/IEC 13213: 1994 [ANSI/IEEE Std 1212, 1994 Edition], Information Technology Microprocessor SystemsControl and Status Register (CSR) Architecture for Microcomputer Buses.

cycle master:

The node that generates the periodic cycle start.

cycle start:

A primary packet sent by the cycle master that indicates the start of an isochronous cycle.

data bit:

The smallest signaling element used by the physical layer for transmission of packet data on the medium one of the PDUs for the physical layer (the other is the arbitration signal).

destination:

A node that is addressed by a packet. If the destination is individually addressed by a source, then it must return an acknowledge packet.

doublet:

Two bytes of data.

dribble bits:

Extra bits added to the end of a packet that allow extra synchronization in implementations.

fairness interval:

A group of backtoback transfers during which each competing source using the fairness protocol gets a single transfer. The delimiters of the fairness interval are arbitration reset gaps.

gap:

A period of idle bus.

initial register space:

The address space reserved for resources accessible immediately after a reset. This includes the registers defined by the CSR Architecture as well as those defined by this specification.

IRM:

Abbreviation for the isochronous resource manager.

isochronous:

The term isochronous indicates the essential characteristic of a timescale or a signal such that the time intervals between consecutive significant instances either have the same duration or durations that are integral multiples of the shortest duration.

isochronous channel:

A relationship between a talker and one or more listeners, identified by a channel number. One packet for each channel is sent during each isochronous cycle. Channel numbers are assigned using the isochronous resource management facilities.

isochronous cycle:

An operating mode of the bus that begins after a cycle start is sent, and ends when a subaction gap is detected. During an isochronous cycle, only isochronous subactions may occur. An isochronous cycle begins every 125 microseconds, on average.

isochronous gap:

The period of idle bus before the start of arbitration for an isochronous subaction.

isochronous resource manager:

The node that contains the facilities needed to manage isochronous resources. In particular, the isochronous resource manager includes the BUS_MANAGER_ID, BANDWIDTH_AVAILABLE, and CHANNELS_AVAILABLE registers. In addition, if there is no bus manager on the local bus, the isochronous resource manager may also perform limited power management and select a node to be the cycle master.

isochronous subaction:

A complete link layer operation (arbitration and isochronous packet) that is sent only during an isochronous cycle.

link layer:

The layer, in a stack of three protocol layers defined for the Serial Bus, that provides the service to the transaction layer of oneway data transfer with confirmation of reception. The link layer also provides addressing, data checking, and data framing, and also an isochronous data transfer service directly to the application.

LINK:

Abbreviation for the link layer.

listener:

A node that receives an isochronous subaction for an isochronous channel. There may be zero, one, or more listeners for any given isochronous channel.

local_bus_ID:

A bus_ID with a value of 11111111112.

lockrequest packet:

The packet transmitted during the request subaction portion of a lock transaction.

lockresponse packet:

The packet transmitted during the response subaction portion of a lock transaction.

lock transaction:

A transaction that passes an address, subcommand, and data parameter(s) from the requester to the responder and returns a data value from the responder to the requester. The subcommand specifies which indivisible update is performed at the responder; the returned data value is the previous value of the updated data.

module:

The smallest component of physical management; i.e., a replaceable device.

natural priority:

The order of packet transmission of a node given that all nodes start arbitration at the same instant using the same priority level. For the cable environment, the closer a node is to the root, the higher is its natural priority. For the backplane environment, the priority level and node_offset are concatenated to give its natural priority.

node:

An addressable device attached to the Serial Bus with at least the minimum set of control registers. Changing the control registers on one node does not affect the state of control registers on another node.

node controller:

A component within a node that provides a coordination point for management functions exclusively local to a given node and involving the application, transaction, link, and physical elements located at that node.

node_ID:

This is a unique 16bit number that distinguishes the node from other nodes in the system. The 10 most significant bits of node_ID are the same for all nodes on the same bus (this is the bus_ID). The six leastsignificant bits of node_ID are unique for each node on the same bus (this is called the physical_ID).

non return to zero (NRZ):

A signalling technique in which a polarity level high represents a logical 1 (one) and a polarity level low represents a logical level 0 (zero).

octlet:

Eight bytes of data.

packet:

A serial stream of clocked data bits. A packet is normally the PDU for the link layer, although the cable physical layer can also generate and receive special short packets for management purposes.

path:

The concatenation of all the physical links between the link layers of two nodes.

payload:

The portion of a primary packet that contains data defined by an application layer.

PCB:

Printed circuit board.

PDU:

Abbreviation for protocol data unit.

peer:

Service layer on a remote node at the same level. For instance a peer link layer is the link layer on a different node.

PHY:

Abbreviation for the physical layer.

PHY packet:

A packet either generated or received by the cable physical layer. These packets are always exactly 64 bits long and the last 32 bits are the bit complement of the first 32 bits.

physical connection:

The fullduplex physical layer association between directly connected nodes. In the case of the cable physical layer, this is a pair of physical links running in opposite directions.

physical_ID:

The leastsignificant 6 bits of the node_ID. This number is unique on a particular bus and is chosen by the physical layer during initialization.

physical layer:

The layer, in a stack of three protocol layers defined for the Serial Bus, that translates the logical symbols used by the link layer into electrical signals on the different Serial Bus media. The physical layer guarantees that only one node at a time is sending data and defines the mechanical interfaces for the Serial Bus. There is a different physical layer for the backplane and for the cable environment.

physical link:

In the cable physical layer, the simplex path from the transmit function of one node's port to the receive function of another directly connected node's port.

port:

A physical layer entity in a node that connects to either a cable or backplane and provides one end of a physical connection with another node.

primary packet:

A packet made up of whole quadlets that contains a transaction code in the first quadlet any packet that is not an acknowledge or a PHY packet.

protocol data unit:

Information delivered as a unit between peer entities that may contain control information, address information and data.

quadlet:

Four bytes of data.

quadlet aligned address:

An address with zeros in the least significant two bits.

request:

A subaction sent by a node (the requester) with a transaction code and optional data to another node (the responder).

response:

A subaction sent by a node (the responder) that sends a response code and optional data back to a requester.

SBM:

Abbreviation for Serial Bus management.

selfID packet:

A special packet sent by a cable PHY during the selfID phase following a reset. One to four selfID packets are sent by a given node depending on the maximum number of ports it has.

Serial Bus management:

The set of protocols, services and operating procedures that monitors and controls the various Serial Bus layers: physical, link, and transaction.

services:

A set of capabilities provided by one protocol layer entity for use by a higher layer or by management entities.

service primitive:

A specific service provided by a particular protocol layer entity.

source:

A node that initiates a bus transfer.

speed code:

The code used to indicate various bit rates for Serial Bus: S25 indicates 24.576 Mbit/sec for TTL backplanes; S50 indicates 49.152 Mbit/sec for BTL and ECL backplanes; S100 indicates 98.304 Mbit/sec base rate for cable; S200 and S400 indicate 196.608 Mbit/sec and 393.216 Mbit/sec for the cable.

split transaction:

A transaction in which the responder releases control of the bus after sending the acknowledge, and then some time later starts arbitrating for the bus so it can start the response subaction. Other subactions may take place on the bus between the request and response subactions for the transaction.

subaction gap:

The period of idle bus between subactions. There is no gap between the request and response subaction of a concatenated split transaction.

subaction:

A complete link layer operation: arbitration, packet transmission and acknowledgment. The arbitration may be missing when a node already controls the bus, and the acknowledge is not present for subactions with broadcast addresses or for isochronous subactions.

talker:

A node that sends an isochronous subaction for an isochronous channel.

transaction layer:

The layer, in a stack of three protocol layers defined for the Serial Bus, that defines a requestresponse protocol to perform bus operations of type read, write, and lock.

transaction:

A request and the corresponding response. The response may be null for transactions with broadcast destination addresses. The PDU for the transaction layer.

unified transaction:

A transaction that is completed in a single subaction.

unit architecture:

The specification document describing the format and function of the unit's softwarevisible resources.