Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus access regulation
Reexamination Certificate
1999-01-29
2002-05-14
Shin, Christopher B. (Department: 2182)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus access regulation
C710S038000, C710S268000, C709S238000, C370S285000, C370S402000
Reexamination Certificate
active
06389496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bridge for performing a transmission/receiving of signals between mutually independent serial buses in a serial bus network constructed with a plurality of terminal devices connected through the serial buses and, particularly, an apparatus and method for initializing the network connected to the bridge and defining a topology and an apparatus and method for transferring packets in the network.
2. Description of Related Art
In response to the request of improvement of the data processing capability of a computer and the request of processing of a large amount of data in such a case of a motion picture, the request of transfer of a large amount of data between devices is being increased recently.
As a serial bus suitable for a transfer of a large amount of data, a high-speed serial bus standardized by IEEE (the Institute of Electrical and Electronics Engineers) 1394 is known. Such high-speed serial bus will be referred to as “IEEE 1394 Serial Bus”, hereinafter, and is disclosed in detail in “IEEE Standard for High Performance Serial Bus” IEEE, Inc., 96.8.
When the IEEE 1394 serial bus is used, it is possible to connect respective terminal devices in a daisy chain connection and to connect them in a star connection by branching a plurality of wiring from each device. Further, it is possible to construct a network in which the daisy chain connection and the star connection are provided in a mixed state.
FIG. 1
shows an example of the network using the IEEE 1394 serial bus.
The IEEE 1394 serial bus transmits data formed according to the CSR architecture defined by IEEE 1212. Data formed according to the CSR architecture forms an address space and upper 16 bits of this address space are used to specify a terminal device. 10 bits among the upper 16 bits represent a bus_ID specifying a serial bus, the remaining 6 bits represent a node_ID specifying the terminal device. Therefore, the network for transmitting data formed according to the CSR architecture can be provided with 1023 buses at maximum and 64 terminal devices at maximum can be connected to each of these buses. Data whose value of bus_ID is 1023 represents data to be transmitted to a local bus, that is, a bus directly connected to a terminal device from which the data is transmitted, and data whose node_ID is 63 represent data to be transmitted to all of the terminal devices in the network, that is, data in “broadcast address”. Therefore, the number of terminal devices which can be connected practically to the network for mutually connecting the terminal devices through a single bus is 63.
In
FIG. 1
, the terminal devices
291
a
to
291
g
are mutually connected through twisted pair lines
292
with feeder lines, each twisted line functioning as a transmission line as well as a feeder line, and the terminal devices apply a predetermined bias voltage to the twisted pair lines
292
.
In the network shown in
FIG. 1
, when an insertion of a new terminal device to the network or a separation of a terminal device connected to the twisted pair line
292
occurs, that is, when a new terminal device is connected to a twisted pair line
292
or a terminal device is disconnected from a twisted pair line
292
, the bias voltage applied thereto is changed. Therefore, an occurrence of the insertion or separation of a terminal device with respect to the twisted pair line can be detected by the terminal devices connected to the twisted pair line by detecting the change of the bias voltage of the twisted pair line.
A terminal device which detects the occurrence of the connection or disconnection of a terminal device with respect to the twisted pair line sends a bus reset signal for initializing the network to the twisted pair line. In response to the bus reset signal, the respective terminal devices cancel a network topology information thereof, that is, information indicative of the bus in the network and the terminal devices connected to the bus, stored therein, to allow the whole network to be initialized. Transmission and/or receiving of packets between the respective terminal devices become impossible during a time in which the network initialization is performed.
After the initialization of the network is completed, a re-definition of topology, that is, update of network topology information, is performed automatically and a route node of the network, that is, a terminal device which manages control rights of the respective buses in the network, is determined. Thereafter, node_ID's are re-assigned to the respective terminal devices. In this case, an isochronous resource manager (IRM) for managing a isochronous source, that is, an isochronous channel for performing an isochronous transmission and a bandwidth to be used, is also determined. Details of this matter is indicated in IEEE 1394.1995 Appendix E.3.1-E.3.4.
Since the initialization of the network and the setting of the terminal devices due to the insertion or separation of terminal devices with respect to the twisted pair lines are automatically performed, a user of the network is not required to be conscious of the state change of the network.
On the network using IEEE 1394 serial bus such as shown in
FIG. 1
, a communication of asynchronous data (data for asynchronous transmission) and isochronous data (data for isochronous transmission) are possible. In the network shown in
FIG. 1
, when a terminal device wishes to transfer a packet, an arbitration sequence defined by IEEE 1394-1995 is performed first. That is, the terminal device requests the root node a bus control right and, when the bus control right is given from the route node to the terminal device, it can transmit the packet. Details of the arbitration sequence is disclosed in IEEE 1394-1995.3.7.3.2.
Further, since it is possible to guarantee the isochronous data transmission in the network using IEEE 1394 serial bus, the isochronous data communication is possible. As mentioned above, in the network shown in
FIG. 1
, one of the terminal devices performs the IRM function of the serial bus network. The terminal device which transmits the isochronous data inquires the IRM of available isochronous resource by using an asynchronous packet before the transmission of the isochronous data. That is, the terminal device reads values of a BANDWIDTH_AVAILABLE register and a CHANNEL_AVAILABLE register which are provided in the IRM and store information indicative of isochronous resource which can be utilized by the network by performing a quadlet read transaction (data read) with using an asynchronous packet having a data structure shown in FIG.
2
.
The terminal device which inquired the available isochronous resource confirms whether or not it is possible to acquire an isochronous resource necessary for transmission of the isochronous data on the basis of the information obtained as a result of the inquiry and, when it is possible to acquire the isochronous resource, the terminal device performs a lock transaction with respect to the IRM by using an asynchronous packet having a data structure shown in FIG.
3
. That is, the terminal device transmits an asynchronous packet which is shown in FIG.
3
and has a value “0002” in its extended_tcode field
64
. Then, contents of the BANDWIDTH_AVAILABLE register and the CHANNEL_AVAILABLE register are compared and swapped with each other. That is, data stored in these registers are compared with data to be written in these registers and portions of the stored data which are different from the data to be written are updated. When the comparison and the swapping are completed, the terminal device becomes in a state in which it can transmit the isochronous data.
Further, in the network using the IEEE 1394 serial bus, one of the terminal devices becomes a route node, as mentioned previously. The terminal device as the route node sends a cycle start packet having a predetermined format to a bus with a predetermined time interval. A terminal device which acquired the isochronous resource of the
Dickstein , Shapiro, Morin & Oshinsky, LLP
NEC Corporation
Shin Christopher B.
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