Controlling the state of a node connected to a bus during...

Details Controlling the state of a node connected to a bus during... Controlling the state of a node connected to a bus during...

2000-10-19

2004-10-12

Chin, Wellington (Department: 2664)

Multiplex communications

Communication techniques for information carried in plural...

Combining or distributing information via frequency channels

C710S100000

Reexamination Certificate

active

06804263

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technique for controlling the state of a node connected to a bus during bus arbitration, and is particularly related to controlling the self identification phase of a device connected to an IEEE 1394 bus. The invention is particularly useful in preventing a given node from transmitting a SELF_ID packet to a parent node when the parent is not yet ready to receive that packet.
2. Description of Related Art
A protocol has been developed for transmitting data at high speeds over a high performance serial bus to which several devices (referred to as “nodes”) are connected, wherein each device may be electrically connected to or disconnected from the bus while the bus is in a “powered on” state. This protocol, known as the IEEE 1394 standard, provides for high speed data transmission and real-time transfer of data between multimedia devices. Consistent with this standard, data transfer speeds of 100 Mbps (the actual data speed is 98.304 Mbps), 200 Mbps (the actual data speed is 196.60 Mbps) and 400 Mbps (the actual data speed is 393.216 Mbps) all may be accommodated on the bus. One device, or node, is connected to another device, or node, by a port; and a port that is operable at a higher data transfer speed also is compatible with a lower data transfer speed. Consequently, devices operable at 100 Mbps, 200 Mbps and 400 Mbps all may be connected in the same data network.
The IEEE 1394 protocol adopts the format known as the data/strobe link (DS-Link) in which data is transferred by using two signals on, for example, two different sets of connectors, with one signal representing the data and the other representing the strobe, such as shown in FIG.
1
. It will be appreciated that the strobe signal is a two-level signal whose state changes when the data level remains the same for consecutive bit cells. By using this DS-Link method, a data clock may be readily recovered by “exclusive-OR-ing” the data and strobe signals.
The cable that is used in the network employing the IEEE 1394 protocol is schematically illustrated in
FIG. 2
as cable
200
, wherein a first twisted pair cable
202
(sometimes referred to as TP A) and a second twisted pair cable
202
′ (sometimes referred to as TP B) are disposed in respective shield layers
201
and
201
′, and these shielded twisted pair cables are further disposed within a second shield layer
204
in which power supply lines
203
also are located. Each twisted pair cable provides data and strobe signals to the nodes that are connected thereto. A more detailed description of the electrical interface between the twisted pair cables and the nodes which are connected by these cables is found in Fire Wire System Architecture IEEE 1394, MindShare, Inc., Don Anderson (1998), which is incorporated herein by reference.
As described in the aforementioned text, signaling between nodes is effected by using both TP A and TP B to which strobe and data drivers are connected. Three signal states are used: 1, 0 and Z, wherein the Z state is represented when a driver is disabled. Before signaling commences, arbitration must be conducted among the nodes to select the proper node that is permitted to acquire the bus. Similarly, when devices are connected to or disconnected from the bus, bus topology reconfiguration automatically is conducted; and this bus topology reconfiguration is analogous to bus arbitration. The states 1, 0 and Z are used to represent control signals, such as shown in Tables 1, 2 and 3; and the transmission of arbitration signals are interpreted in the manner represented by Tables 4 and 5.
TABLE 1
Transmit
arbitration
signal A
Drivers
(Arb_A-Tx)
Strb_Tx
Strb_Enable
Comment
Z
—
0
TPA driver is disabled
0
0
1
TPA driver is enabled,
strobe is low
1
1
1
TPA driver is enabled,
strobe is high
TABLE 2
Transmit
arbitration
signal A
Drivers
(Arb_A-Tx)
Strb_Tx
Strb_Enable
Comment
Z
—
0
TPA driver is disabled
0
0
1
TPB driver is enabled,
data is low
1
1
1
TPB driver is enabled,
data is high
TABLE 3
Received
Transmitted
arbitration
arbitration
Interpreted
comparator
signal for
arbitration
Value
this port
signal
(Arb_n
a
—
(Arb_n
a
—
(Arb
—
Rx)
Tx)
n
a
)
Comment
Z
Z
Z
If this port is transmitting a Z,
0
Z
0
then the received signal will be
1
Z
1
the same as transmitted by the
port on the other end of
the cable.
Z
0
1
If the comparator is receiving a
Z while this port is sending a 0,
then the other port must be
sending a 1. This is the first
half of the 1's dominance
rule.
0
0
0
The other port is sending a
0 or a Z.
Z
1
1
The other port must be
sending a 0.
This is the other half of
the 1's dominance rule.
1
1
1
The other port is sending
a 1 or a Z.
TABLE 4
arbitration transmit
(Arb
—
(Arb_B
—
A-Tx)
Tx)
Line state name
Comment
Z
Z
IDLE
sent to indicate a gap
Z
0
TX_REQUEST
sent to parent to
request the bus
TX_GRANT
sent to child when bus
is granted
0
Z
TX_PARENT
—
sent to parent candi-
NOTIFY
date during tree-ID
0
1
TX_DATA
—
sent before any packet
PREFIX
data and between
blocks of packet data
in the case of
concatenated
subactions
1
Z
TX-CHILD-
sent to child to
NOTIFY
acknowledge the
parent_notify
TX_IDENT
—
sent to parent to indi-
DONE
cate that self-ID is
complete
1
0
TX_DATA
—
sent at the end of
END
packet transmission
1
1
BUS_RESET
sent to force a bus
reconfiguration
TABLE 5
Interpreted
arbitration
signals
Arb_A
Arb_B
Line state name
Comment
Z
Z
IDLE
the attached peer PHY is inactive
Z
0
RX
—
the attached peer PHY wants
PARENT
—
to be a child
NOTIFY
RX
—
attached peer PHY has abandoned a
REQUEST
—
request (this PHY is sending a grant)
CANCEL
Z
1
RX_IDENT
—
the child PHY has completed
DONE
its self-ID
0
Z
RX_SELF
—
the parent PHY is granting the
ID_GRANT
bus for self-ID
RX
—
a child PHY is requesting the bus
REQUEST
0
0
RX_ROOT
—
the attached peer PHY and
CONTEN-
this PHY both want to be a child
TION
RX_GRANT
the parent PHY is granting
control of the bus
0
1
RX
—
attached peer PHY acknowledges
PARENT
—
parent_notify
HANDSHAKE
RX
—
the attached peer PHY has finished
DATA
—
sending a block of data
END
is about to release the bus
1
Z
RX_CHILD
—
attached peer PHY acknowledges
HANDSHAKE
TX_CHILD_NOTIFY
(the peer PHY is a child of this PHY)
1
0
RX_DATA
—
the attached peer PHY is about to
PREFIX
send packet data or has finished
sending a block of packet data
and is about to send more
1
1
BUS_RESET
send to force a bus reconfiguration
Device configuration occurs locally on the bus without the intervention of a host processor. Each time a new device, or node, is connected to or disconnected from the bus, the entire bus is reset and reconfigured. This is what has been mentioned above as automatic topology reconfiguration. Bus reconfiguration is executed by first performing bus initialization, then performing tree identification and finally performing self identification. In the bus initialization phase, all the nodes return to their initialized states regardless of their prior configurations. That is, all topology information is cleared from the nodes. The only information known to a node is whether that node is a branch (that is, whether the node is connected to two or more nodes) or a leaf (that is, whether the node is connected to only one other node) or is isolated.
FIG. 3A
schematically illustrates a network consisting of branch and leaf nodes at the bus initialization phase.
In the tree identification phase, the entire network topology is viewed as a single tree. The aforementioned Fire Wire System Architecture text describes that after tree identification, one node has the status of the root node; and all connections to the root node are identified as “root” directions toward the root node. Nodes are connected by connecting one port to another; and the port closest to the root node is referred to as the “parent” port. Parent ports are connected to “child” ports; and the node that is connected only to “child” nodes, that is, the node whose ports are connected only to parent ports, is the root node.
FIG. 3B
illustrates the network after completing the

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