United States Patent
`
`[19]
`
`Patel et al.
`
`[11] Patent Number:
`
`5,883,894
`
`[45] Date of Patent:
`
`Mar. 16, 1999
`
`[54]
`
`SHARED AUTO-NEGO'l‘lA'l‘l()N LOGIC FOR
`
`OTHER PUBLICATIONS
`
`US005883894/\
`
`[75]
`
`MULTIPLE PORT NET“ ORK DEVICES
`Inventors; Sandeep A. Patel, Cupertino; Claude
`G. Hayek, Mountain View, both of
`Ca11f_
`
`[73] Assignee: 3Com Corporation, Santa Clara, Calif.
`
`[21] Appl. No.: 774,480
`
`[22]
`
`Filed:
`
`Dec. 30, 1996
`
`I"t- Cl-6 --------------------------------------------------- H041‘ 12/413
`[51]
`[52] U-S- CL .......................... 370/433; 370/447; 370/449;
`370/492
`370/465, 466,
`[58] Field of Search
`370/401, 437, 438, 439, 445, 447, 449,
`458, 461, 462
`
`[561
`
`Referenees Cited
`
`5/1994 samba_u1u111,y .... .
`5,311,114
`7/1995 Cmyford ,,
`5,432,775
`8/1996 Caspi et al.
`5,546,385
`5,586,117 12/1996 Edem et al
`5,610,903
`3/1997 Crayford
`5,617,418
`4/1997 Shirani et al.
`
`.... ..
`
`
`
`, , , , , I . U 370/296
`.370/248
`. 370/412
`. 370/466
`. 370/213
`
`“Physical Layer Link Signaling for 10 Mb/s and 100 Mb/s
`?1L;t§g)N°g°tiati°n 0“ Twistcd Pair”: IEEE,
`1313- 235—280
`e
`'
`‘
`Primary Examiner—Alpus H. Hsu
`Attorney, Agent, or Firm—Wilsoii Sonsini Goodrich &
`Rosati
`[57]
`
`ABSTRACT
`.
`1
`1
`.
`.
`A device interconnects across links, a plurality of terminals
`having respective modes of operation. The device includes
`a plurality of ports [or connection to respective links, and
`1Og1c ¢0up1ed to 1113 p1u[a111y of P0115 10 gxgfcjsc an auto-
`negotiation protocol with terminals coupled to the respective
`links to resolve modes of operation. The logic includes a
`shared unit for executing the auto-negotiation protocol, and
`an arbiter unit for arbitrating among the plurality ofports for
`use of the shared unit. The arbiter connects ports in the
`plurality of ports to the shared unit
`in a round robin
`. M
`f
`'
`l
`f
`-
`Tilufififi Th°§§§£l1§§i2‘§i§§§i1§th?fli§$‘f§7i§r$Jf§§ZZt
`f.t(t..'
`1.’.
`,(d'
`.
`.
`ibl..
`f
`
`operation resolved by the shared auto-negotiation uiiit
`include LAN technology supported by terminals on the
`corresponding links, such as IEEE 802.3 Local Area Net-
`work technologies,
`
`12 Claims, 4 Drawing Sheets
`
`(‘107—o
`END STA.
`(1OBASE-T)
`
`
`
`107-1
`(E3§A:lEA‘l’
`FULL‘
`DUPLEX)
`
`END STA.
`(1ODBASE-
`
`
`
`I——————————————————————————————— — -1
`:
`
`MANAGEMENT
`PR0CESS0|:o4
`T
`REPEATER
`CORE
`M
`
`SHARED AUTo-
`NEGOTIATE
`LOGIC UNIT.”
`-—
`
`FRAME BUFFER
`E
`
`I 5
`
`‘
`E
`:
`E
`i
`3
`‘
`
`1
`.
`
`} 3
`
`4:}
`
`<—>
`
`102-2
`
`
`
`<—>
`END STA.
`
`(1ODBASE-
`TX FULL
`
`DUPLEX)
`
`Aerohive - Exhibit 1034
`
`
`
`END STA.
`
`(100BASE-
`T4)
`
`Aerohive - Exhibit 1034
`
`

`
`U.S. Patent
`
`Mar. 16,1999
`
`Sheet 1 014
`
`5,883,894
`
`1 07-0
`
`
`
`MANAGEMENT
`PROCESSOR
`
`104
`
`101
`
`REPEATER
`CORE
`
`END STA.
`
`(1 OBASE-T)
`
`106-1
`
`107"
`
`END STA.
`
`(103/*5E‘T
`FULL
`
`DUPLEX)
`
`II
`
`1
`‘
`
`PORTO
`
`102-0
`
`mm
`
`END STA.
`(100BASE—
`TX)
`
`E ;
`
`1
`
`PORT 1
`
`SHARED AUTO-
`
`NEGOTIATE
`
`
`LOGIC UNIT1 1
`
`
`
`
`FRAME BUFFER
`
`351
`
`DUPLEX)
`
`END STA.
`(100BASE-
`TX FULL
`
`PORT n-1
`
`T4)
`
`(1 O0BASE-
`
`END STA.
`
`

`
`U.S. Patent
`
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`

`
`U.S. Patent
`
`Mar. 16,1999
`
`Sheet 3 of4
`
`5,883,894
`
`RESET
`
`301
`
`IDLE
`Set x = o
`
`302
`
`300
`
`303
`
`Round-Robin_State
`
`Poll Status of Port X 304
`
`AN Status Reg_X = 1
`
`306
`
`AN Status Reg_X = 0
`OR
`
`Management__Renegotiate
`
`305
`
`Start 200ms
`Timer
`
`
`
`200ms Timer
`
`Expired
`
`308
`
`309
`
`
`AN_Port_X
`(set Port X
`Selector, and
`assert
`
`310
`
`
`
`Renegotiate)
`
`AN Done for Port X
`
`313
`
`311
`
`Write_AN Status
`
`Reg_X 312
`
`FIG. 3
`
`

`
`U.S. Patent
`
`Mar. 16,1999
`
`Sheet 4 of 4
`
`5,883,894
`
`401
`
`AN-
`STATUS
`
`REG_X
`
`400
`
`402 T)
`
`DONE_X
`
`CLK
`
`
`
`RESET
`
`UNK_OK_X
`
`403
`
`407
`
`FIG. 4
`
`

`
`5,883,894
`
`1
`SHARED AUTO-NEGOTIATION LOGIC FOR
`MULTIPLE PORT NETVVORK DEVICES
`
`BACKGROUND OF THE INVENTION
`
`I. Field of the Invention
`Present invention relates to network intermediate devices
`for interconnecting terminals in a network across commu-
`nication links; and more particularly to techniques used to
`resolve modes of operation for the links.
`2. Description of Related Art
`Communication networks consist of terminals that are
`interconnected by links to network intermediate devices
`such as repeaters, switches, bridges and the like. The inter-
`mediate devices are used to interconnect the terminals to
`establish paths of communication among the terminals.
`As network technologies have developed, a wide variety
`of techniques have evolved for operating links between
`terminals and intermediate devices. For example, the ether-
`net network standard according to the IEEE Standard 802.3,
`published by the Institute of Electrical and Electronic
`Engineers, supports a variety of local area network (LAN)
`technologies. These technologies include the 10 BASE-T
`standard which specifies a 10 megabit per second carrier
`sense multiple access with collision detection (CSMA/CD)
`LAN over two pairs of twisted pair telephone wire, the 10
`BASE-F standard which specifies a 10 megabit per second
`CSMA/CD LAN over fiber optic cable; the 100 BASE-TX
`standard specifies a 100 megabit per second CSMA/CD
`LAN over two pairs of category live UTP or shielded twisted
`pair wire, and a number of other current and emerging
`technologies. Typically data terminals in a network are
`designed to support a specific LAN technology. However,
`network intermediate devices which are designed to inter-
`connect a wide variety of terminals, need a technique for
`resolving the particular technology used across a link
`coupled to a particular port of the device.
`To meet this need for resolving the LAN technology of a
`particular link the IEEE standards commissions have devel-
`oped an auto—negotiation function which specifies physical
`layer signaling for 10 megabit per second and 100 megabit
`per second LAN technologies which utilize twisted pair
`wiring. These technologies include 10 BASE-T, 10 BASE-T
`f11ll duplex, 100 BASE-TX, 100 BASE-TX full duplex, and
`100 BASE-T4. The specified a11to-negotiation function is
`designed to support other technologies and new LAN tech-
`nologies as they evolve.
`'I'he auto—negotiatioi1 function
`according to the standard allows a device to advertise
`enhanced modes of operation that it possesses to a device at
`the remote end of a link, and to detect corresponding
`enhanced modes of operation that the other device may be
`advertising. The auto—negotiation function automatically
`configures both devices to take maximum advantage of their
`abilities. The auto—negotiation function is performed at the
`physical layer relying on link integrity test pulse sequences
`(including normal link pulses NLPs and fast link pulses
`FI.Ps), so that no packet or upper layer protocol overhead is
`added to network devices for the purposes of this function.
`The auto—negotiation function is specified in clause 28 of
`IEEE Standard 802.3u-I995, Institute of Electrical and
`Electronic Engineers, Inc., pages 235-280, and associated
`annexes. Clause 28 is incorporated by reference as if fully
`set forth herein.
`
`The auto—negotiation function is designed for i1nplemen-
`tation in the physical layer of each port on the network
`intermediate devices which utilize the standard. See Clause
`
`2
`28, supra, figure 28-2 “Location ofA11to-Negotiation Func-
`tion within the ISO Reference Model” on page 237. Thus, a
`twelve port repeater or other intermediate device, will have
`twelve iiistaiitiatioiis of the auto—negotiation state machine.
`The auto—negotiation state machine is quite complicated,
`encompassing thousands of logic gates. Thus,
`the auto-
`negotiation function significantly increases the cost of net-
`work intermediate devices.
`
`10
`
`Accordingly, it is desirable to provide an auto—negotiation
`function for network intermediate systems, with a more
`efficient architecture, so that expensive space on integrated
`circuits implementing the ports can be saved.
`SUMMARY OF THE INVENTION
`
`According to the present invention a device having an
`improved auto—negotiation function architecture is provided
`that
`interconnects across links, a plurality of terminals
`having respective modes of operation. The device includes
`a plurality of ports for connection to respective links, and
`logic coupled to the plurality of ports to exercise an auto-
`negotiation protocol with terminals coupled to the respective
`links to resolve modes of operation. The logic includes a
`shared unit for executing the auto—negotiation protocol, and
`an arbiter unit for arbitrating among the plurality of ports for
`use of the shared unit. In one preferred embodiment, the
`arbiter includes logic which connects ports in the plurality of
`ports to the shared unit in a round robin sequence.
`According to another aspect of the invention, the device
`includes memory storing a set of status signals for respective
`ports. The status signals indicate one of a resolved state and
`an unresolved state for
`the corresponding ports. The
`resolved state indicates that a mode of operation has been
`resolved for the link on the corresponding port. The unre-
`solved state indicates that the mode of operation has not
`been resolved for the link on the corresponding port. The
`arbiter logic polls the memory to read the set of status
`signals in sequence, and in response enables use of the
`shared auto—negotiation unit by the ports.
`According to another aspect of the invention, the shared
`a11to-negotiation 1Init generates a signal upon successful
`resolution of a mode of operation for a corresponding port.
`Logic is responsive to said signal to write the status signals
`in the memory.
`the
`According to a preferred aspect of the invention,
`modes of operation resolved by the shared auto—negotiation
`unit include LAN technology supported by terminals on the
`corresponding links. More preferably, the LAN technologies
`comprise IEEE 802.3 Local Area Network technologies.
`According to yet another embodiment, the shared auto-
`negotiation 11nit comprises an auto—negotiation function
`specified according to IEEE Standard 802.3u, clause 28.
`The present invention can also be characterized as a
`method for automatically negotiating a mode of operation
`for a set ofports on a network device. The method comprises
`the steps of:
`monitoring status of ports in the set of ports according to
`a sequence to determine whether a mode of operation
`is resolved or unresolved for selected ports in the
`sequence;
`for a selected port in the sequence, if the status indicates
`that a mode of operation is unresolved, then connecting
`the selected port to a shared auto—negotiation unit and
`executing an auto—negotiation protocol for the selected
`port to resolve a mode of operation; and
`changing the status of the selected port from unresolved
`to resolved, and returning to the step of monitoring.
`
`30
`
`40
`
`45
`
`50
`
`60
`
`

`
`5,883,894
`
`U1
`
`10
`
`30
`
`40
`
`45
`
`50
`
`3
`In accordance with the techniques discussed above, the
`method of the present
`invention includes storing status
`signals for the ports indicating whether the mode of opera-
`tion is resolved or unresolved, and the status of ports is
`monitored by polling the stored status signals.
`According to another aspect of the invention, the network
`intermediate device which includes the shared a11to-
`negotiation unit according to the present invention, com-
`prises a repeater. In alternative syster11s, the intermediate
`device comprises a switch or a bridge.
`According to one embodiment of the present invention, a
`master state machine is coupled with a shared auto-
`negotiation state machine to be used by multiple ports in a
`network device. The master state machine operates at net-
`work device power up to connect the auto—negotiation state
`machine to one port at a time. The master state machine
`connects the shared auto—negotiation state machine to a next
`port when auto—negotiation is complete for the current port,
`or a timer has expired. During normal operation, after the
`power up sequence is complete, the master state machine
`checks each port for link status. If the link status is OK for
`the port being checked, then the master state machine moves
`to a next port. If the link status is not OK, then the master
`state machine connects the auto—negotiation state machine to
`the port, and waits for auto—negotiation to successfully '
`complete, or a timer to expire. This sequence is repeated by
`the master state machine in a round robin sequence. Once
`auto—negotiation is complete on a particular port, the link
`integrity state machine on the port brings the status of the
`link up. The link status check allows the auto—negotiation
`state machine to move to the next port, and reduces the
`overall time required to bring up link status on all ports of
`the network device.
`Accordingly, a shared auto—negotiation state machine is
`provided for network intermediate devices, based on a
`realization that in multiple port network devices, it is not
`necessary that all links be brought up simultaneously or in
`parallel. Furthermore, the invention is useful in any network
`device which has multiple ports, such as repeaters, bridges
`and switches.
`In summary, the present invention allows network devices
`with multiple ports to be implemented with a shared auto-
`negotiation state machine and a simple master state machine
`which arbitrates use of the shared unit. This provides sub-
`stantial cost advantages over the prior art by red11cing the
`complexity of logic required on each port.
`Other aspects and advantages of the present invention can
`be seen upon review of the figures, the detailed description
`and the claims which follow.
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`FIG. 1 is a simplified block diagram of a network includ-
`ing an intermediate device with a shared auto—negotiation
`logic unit according to the present invention.
`FIG. 2 is a more detailed block diagram of a inultiport,
`shared auto—negotiation device according to the present
`invention.
`
`FIG. 3 is a state diagram illustrating operation of the
`master state machine of FIG. 2.
`
`60
`
`FIG. 4 is a simplified diagram of an auto—negotiation
`status register for use in the system of FIG. 2.
`DETAILED DESCRIPTION
`
`A detailed description of preferred embodiments of the
`present
`invention is provided with respect
`to FIGS. 1
`through 4, in which FIG. 1 illustrates a network intermediate
`
`4
`device 100 including a shared auto—negotiation function
`according to the present invention. In FIG. 1, the network
`intermediate device 100 comprises a repeater, and includes
`a repeater core state machine 101 and shared autonegotiate
`unit 110 according to the present invention. In alternative
`systems, the network intermediate device 100 consists of a
`switch or a bridge, or other technology used for intercon-
`necting network terminals.
`The device 100 includes a set of ports, including port (0)
`102-0 through port (n—1) 102—n—1. The set of ports 102-0
`through 102-n—I is coupled to the repeater core 101 and
`shared autonegotiate 11nit 110 across bus 103. In addition, a
`repeater management processor 104 and optionally a frame
`buller 105 are included, and coupled to the bus 103.
`In alternative architectures, the set of ports 102-0 through
`102-n—l
`is coupled directly to the repeater core in a star
`configuration. Also, other interconnection technologies can
`be used depending on the particular environment.
`Ports in the set of ports 102-0 through 102—n—1 are
`coupled to respective links 106-0 through 106-r1—1. A plu-
`rality of end stations 107-0 through 107—n—1 are coupled to
`the links 106-0 through 106-n—1 respectively. Each of the
`end stations (or other network terminals) has a respective
`mode of operation according to the LAN technology sup-
`ported by the terminal. In the example of FIG. 1, end station
`I07-0 supports 10 BASE-T technology. End station 107-1
`supports 10 BASE-T full duplex technology. End station
`107-2 supports 100 BASE-TX technology. End station
`107-3 supports 100 BASE-TX full duplex technology. End
`station 107—n—1 supports 100 BASE—'I'4 technology.
`According to the present invention, rather than imple-
`menting an auto—negotiation state machine in each of the
`ports 102-0 through 102—n—1, a shared auto—negotiation 11nit
`110 is coupled to the set of ports. The shared autonegotiate
`logic performs the IEEE 802.3u Clause 28 auto—negotiation
`function in a preferred system, to automatically resolve a
`mode of operation for each of the ports for the twisted pair
`wiring based technologies specified according to 802.3
`CSMA/CD networks.
`Implementation of the shared auto—negotiation unit 110 is
`illustrated in FIG. 2. In FIG. 2, the architecture is illustrated
`for an IEEE compliant 802.3 auto—negotiation function.
`Thus, a shared auto—negotiation function unit 200 is pro-
`vided. The set of ports 107-0 through 107—n—1 is shown.
`Coupled with each port is a link state machine 201-0 through
`201—n—1. The link pulses received and transmitted through
`the ports in the set of ports 107-0 through 107-n—1 are
`coupled to a selector 202 across lines 203-0 through 203-
`n—1. The selector comprises an n-to-1 port multiplexer
`which connects the received link pulses from a selected port
`across line 204 to the shared auto—negotiation function 200,
`and supplies the link pulses which are transmitted by the
`auto—negotiation function 200 across line 205 to the selected
`port. A shared auto—negotiation master state machine 206
`generates a PORT X SELECTOR signal on line 207, which
`controls the selector 202. Link status signals, including the
`I.INK_OK signal from the selected port are supplied on line
`208 to the master state machine 206. Also, when the auto-
`negotiation function 200 completes resolving the mode of
`operation for a select port, a DONE signal is supplied to the
`master state machine 206 on line 209. Other inputs to the
`master state machine 206 include a management renegotiate
`signal on line 210, and a RESET signal on line 211. The
`shared autonegotiate master state machine 206 selects a
`current port, and issues a RENEGOTIATE signal on line 212
`to the shared unit 200. After the RENEGOTIATE signal is
`
`

`
`5
`issued, and the master state machine 206 waits to receive a
`DONE signal on line 209, or until expiration of the timer as
`discussed below.
`
`5,883,894
`
`6
`register 401 is supplied on line 402, from the DONE line 209
`of FIG. 2. The clock signal 403 clocks the register 400 with
`appropriate timing under control of the state machine. The
`register 400 is reset by a signal oi1 line 404. 'l'he signal on
`line 404 is supplied at the output of OR gate 405. The inputs
`to OR gate 405 include the RESET signal 406 which
`corresponds to the RESET signal 301 in FIG. 3 (also the
`RESET signal 211 in FIG. 2). The other input to the OR gate
`405 comprises tl1e output of inverter 407. The input to the
`inverter 407 is the LINK OK X signal on line 408. This
`signal corresponds to the LINK_OK signal on the line 208
`of FIG. 2, for a selected port X. Thus, the register 400 is
`cleared at power on reset, or when the LINK_OK signal for
`port X is at logic 0, indicating that the link is down. The
`register is written by the master state machine when the port
`has been successfully autonegotiated as indicated by the
`DONE signal on line 402.
`In conclusion, the present invention provides for the use
`of shared auto-negotiation state machine on a network
`intermediate device. A master state machine arbitrates
`among the ports on the device for use of the shared auto-
`negotiation state machine. The invention is applicable to any
`network device which has multiple ports, such as repeaters,
`bridges and switches. According to the present invention,
`substantial savings in integrated circuit complexity are
`made, without compromising functionality of the device,
`because it
`is unnecessary that auto-negotiation state
`machines operate in parallel on a multiple ports in a single
`device. Rather, a shared a11to—negotiation state machine can
`effectively serve many ports in a single network intermedi-
`ate device.
`
`The foregoing description of a preferred embodiment of
`the invention has been presented for purposes of illustration
`and description. It is not intended to be exhaustive or to limit
`the invention to the precise forms disclosed. Obviously,
`many modifications and variations will be apparent to prac-
`titioners skilled in this art. It is intended that the scope of the
`invention be defined by the following claims and their
`equivalents.
`What is claimed is:
`1. Adevice which interconnects across links a plurality of
`terminals having respective modes of operation, comprising:
`a plurality of ports for connection to respective links;
`memory storing a set of status signals, status signals in the
`set
`indicating states of corresponding ports in the
`plurality of ports, wherein status signals in the set
`indicate one of a resolved state and an unresolved state,
`the resolved state indicating that a mode of operation
`has been resolved for the link on the corresponding
`port, and the unresolved state indicating that a mode of
`operation has been not resolved for the link on the
`corresponding port;
`a shared unit coupled to the plurality of ports to exercise
`an auto-negotiation protocol with terminals coupled the
`respective links to resolve modes of operation for the
`respective links, wherein the modes of operation
`resolved by the shared unit include local area network
`LAN technologies supported by terminals on the cor-
`responding links; and
`arbiter logic which polls the memory to read the set of
`status signals in a sequence, and in response to status
`signals in the set, enables use of the shared unit by the
`corresponding ports.
`2. The device of claim 1, wherein the arbiter logic
`comprises logic to poll
`the memory in a round robin
`sequence.
`
`The status signals for the individual ports are stored in the
`autonegotiate status registers 213 which are coupled with the
`master state machine 206 in this example. When the mode
`of operation for a particular port is successfully resolved,
`then the master state machine writes a resolved status to the
`corresponding status register. When,
`the status register
`stores a status signal indicating an unresolved state,
`the
`master state machine 206 periodically retries to resolve a
`mode of operation.
`the operation of the
`FIG. 3 illustrates in more detail,
`master state machine 206 in FIG. 2. The master state
`machine includes an idle state 300, in which a port selector
`parameter X is set to 0. The idle state 300 is entered by
`assertion of the RESET signal as indicated byline 301. Froi11
`the idle state, the state machine transitions on line 302 to a
`round robin state 303. In state 303, the status of port X is
`polled. If the status is resolved, indicated by a logic 1 stored
`in the corresponding status register, then the state machine
`transitions on line 304 to state 305, where the parameter X
`is incremented,
`i11odulo n—l, After the parameter X is
`incremented, the algorithm loops back to the round robin
`state 303 to test the next port so that the ports are polled in V
`a round robin fashion. Other polling sequences may also be
`used, including priority based sequences or user specified
`sequences as suit a particular environment.
`If in state 303, the corresponding status register indicates
`that the port is in an unresolved state, corresponding to a
`logic 0 in the corresponding register, or if a management
`renegotiate signal is received for port X, then the algorithm
`transitions on line 307 to state 308 where a 200 millisecond
`timer is started. Of course the length of the timer is deter-
`mined according to a number of factors such as auto-
`negotiation protocol used, and can be optimized to meet a
`particular situation.
`Next,
`the algorithm transitions from state 308 to the
`autonegotiate state 309, where the port X selector signal on
`line 207 is set to select port X, and the RENEGOTIATE
`signal is asserted on line 212. At state 309, the algorithm
`transitions on line 310 back to the increment state 305, if the
`timer expires before auto-negotiation is completed.
`If the DONE signal is received from line 209 before the
`timer expires, then the master state machine transitions on
`line 311 to state 312, where the status register for the
`corresponding port is written with a resolved status signal,
`corresponding to a logic 1 in this example. After writing
`status, then the algorithm transitions on line 313 back to the
`state 305 to increment the parameter X.
`Thus, initially, when the master state machine transitions
`from the idle to the round robin states, the port selector is set
`to port 0. The selector gets incremented one by one until it
`reaches n—l, for a total of 11 ports. X can also be set by the
`management entity, if the latter needs to renegotiate on a
`certain port. Atimer, in this example, 200 milliseconds starts
`for port X, when the master state machine enters the state
`309 to autonegotiate for port X. The timer gets reset upon
`entering the round robin state 303. The timer serves as a
`“move to next port” indicator, if the mode of operation of the
`port cannot be successfully renegotiated.
`FIG. 4 illustrates the auto-negotiation status register for
`an individual port, used as a memory 213 in system of FIG.
`2. Thus, a D-type register 400 in this example, stores an
`auto-negotiation status signal AN STATUS REG_X, and
`outputs the status signal on line 401. The D input for the
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`3. The device of claim 1, comprising:
`a selector responsive to the arbiter unit, having a plurality
`of inputs coupled to corresponding ports in the plurality
`of ports, and having an output coupled to the shared
`unit.
`4. The device of claim 1, wherein the shared unit gener-
`ates a signal upon successful resolution of a mode of
`operation for a corresponding port, and including logic
`responsive to said signal to write status signals in the set to
`the memory.
`5. The device of claim 1, wherein the modes of operation
`resolved by the shared unit include IEEE 8023 local area
`network LAN technologies supported by terminals on the
`corresponding links.
`6. The device of claim 5, wherein the auto-negotiation
`protocol executed by the shared unit comprises an auto-
`negotiation function specified according to IEEE Standard
`8023.
`7. Adevice which interconnects across links a plurality of
`terminals having respective modes of operation, comprising:
`a plurality of ports for connection to respective links;
`logic coupled to the plurality of ports to exercise a
`protocol with terminals coupled the respective links to
`resolve modes of operation for the respective links, the ,
`logic including a shared unit for executing the protocol;
`and
`
`an arbiter unit for arbitrating among the plurality of ports
`for use of the shared unit, the arbiter unit comprising:
`memory storing a set of status signals, status signals in
`the set indicating states of corresponding ports in the
`plurality of ports, and
`logic which polls the memory to read the set of status
`signals in a sequence, and in response to status
`signals in the set, enables use of the shared 11nit by
`the corresponding ports.
`8. The device of claitu 7, wherein status signals in the set
`indicate one of a resolved state and an unresolved state, the
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`resolved state indicating that a mode of operation has been
`resolved for the link on the corresponding port, and the
`unresolved state indicating that a mode of operation has
`been not resolved for the link on the corresponding port.
`9. The device of claim 8, wherein the shared unit gener-
`ates a signal upon successful resolution of a mode of
`operation for a corresponding port, and including logic
`responsive to said signal to write status signals in the set to
`the memory.
`10. A method for automatically negotiating a mode of
`operation for a set of ports on a network device, comprising:
`monitoring status of ports in the set of ports according to
`a sequence to determine whether a mode of operation
`is resolved or unresolved for selected ports in the
`sequence;
`for a selected port in the sequence, if the status indicates
`that a mode of operation is unresolved, then connecting
`the selected port to a shared auto-negotiation unit and
`executing an auto-negotiation protocol for the selected
`port to resolve a mode of operation for the selected
`port;
`storing status signals in memory for the set of ports
`indicating for ports in the set whether a mode of
`operation is resolved or unresolved; and
`changing the status of the selected port froi11 unresolved
`to resolved, and returning to the step of monitoring,
`said monitoring step includes polling the stored status
`signals.
`11. The method of claim 10, wherein the step of moni-
`toring includes polling the stored status signals according to
`a round robin sequence.
`12. The method of claim 10, including generating a signal
`upon successful resolution of a mode of operation for the
`selected port, and writing in response to said signal the status
`signals in the set to memory.
`X
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