Abstract:
A first physical layer device of a first network device includes a sense circuit that senses activity on a medium and with the first physical layer device. An autonegotiation circuit attempts to establish a connection with a second physical layer device of a second network device within a first period after the sense circuit senses activity. An energy saving circuit selectively provides power to the first physical layer device based on the sensed activity and connection with the second physical layer device, and that while attempting to establish the connection resets a timer associated with the first period when the sense circuit senses activity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a divisional of application Ser. No. 09/990,137 filed on Nov. 21, 2001 now U.S. Pat. No. 6,993,667 which claims priority from U.S. Provisional Application Ser. No. 60/256,117, filed on Dec. 15, 2000 which are both hereby incorporated by reference in their entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to network devices, and more particularly to energy saving circuits that are associated with the physical layer of network devices. 
   BACKGROUND OF THE INVENTION 
   Servers, storage devices, computers, printers, switches and other electronic devices are often connected together to form a network to allow the exchange of data. The network devices include a physical layer that usually includes network cards and cables that establish and maintain the connection between the network devices. In 10BASE-T, 100 BASE-TX, and 1000BASE-T networks, the physical layer executes autonegotiation protocols that initiate the data link between the network devices. Once the data link is lost, the physical layer notifies the network device. The cable usually provides the physical connection between the physical layers of network devices. 
   During autonegotiation, bursts of pulses called fast link pulse (FLP) bursts are transmitted and received periodically by the physical layer. The purpose of the FLP bursts is to detect the presence of another network device and to initiate the exchange of data between the network devices. The initialization information typically includes configuration information such as the communication speed(s) that are available and other information that will be necessary for subsequent communications between the network devices. 
   When a physical layer of a network device is not connected to another network device, the physical layer still periodically transmits FLP bursts in an attempt to initiate connections to other network devices. FLP bursts usually include 17 to 33 link pulses that are generated every 16 ms. The physical layer remains powered up while attempting to connect to another network device. 
   Laptop computers are sensitive to the use of power due to the limited power that is available from the batteries. Continuously powering the physical layer when the laptop computer is not already connected to another network device is not an efficient use of the laptop computer&#39;s battery power. One way to reduce power consumption is for the laptop computer to completely power down the physical layer when the laptop computer is not connected to another network device. However, if another network device is attempting to establish a data link with the laptop computer, there is no way for the powered-down physical layer to detect the presence of the other network device. Even when the network device is not battery powered, reducing power consumption reduces heat that is generated by the network device. 
   SUMMARY OF THE INVENTION 
   A physical layer device comprises a sense circuit that senses activity on a medium. An autonegotiation circuit attempts to negotiate a link with a second physical layer device of a second network device after the sense circuit senses activity. An energy saving circuit selectively provides power to the physical layer device based on the sensed activity, times a first period which is reset when the sense circuit senses activity, and powers down the physical layer device when the autonegotiation circuit fails to establish the link with the second physical layer device within the first period. 
   In other features, a link circuit communicates with the autonegotiation circuit and triggers the link state when autonegotiation is complete and a link with the second physical layer device is established. The link circuit generates a link lost signal when the link is lost. 
   A physical layer device comprises a transmitter and a receiver. A sense circuit communicates with the transmitter and the receiver, senses activity on a medium and times a second period which is reset when activity is sensed. An autonegotiation circuit attempts to negotiate a link with a second physical layer device of a second network device after the sense circuit senses activity. An energy saving circuit selectively provides power to the physical layer device based on the sensed activity. The sense circuit turns on the transmitter after the second period, the transmitter generates a signal on the medium, and the sense circuit turns off the transmitter. 
   In other features, the second period is longer than a period of fast link pulse bursts. 
   A physical layer device comprises a sense circuit that senses activity on a medium. A autonegotiation circuit attempts to negotiate a link with a second physical layer device of a second network device after the sense circuit senses activity. An energy saving circuit selectively provides power to the physical layer device based on the sensed activity. A switching circuit senses a connection configuration of the second physical layer device and that adjusts an MDI/MDIX connection configuration of the physical layer device to complement the MDI/MDIX connection configuration of the second physical layer device. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  illustrates a plurality of network devices according to the prior art that include physical layers; 
       FIG. 2  illustrates a network device according to the present invention including a physical layer with an energy saving circuit; 
       FIG. 3  illustrates the energy saving circuit, other physical layer circuits, a receiver and a transmitter; 
       FIG. 4  illustrates the operation of the energy saving circuit of  FIG. 2  in further detail; 
       FIG. 5  is a flowchart illustrating steps that are performed in a first energy saving mode; 
       FIG. 6  illustrates two network devices according to the present invention that are connected to a network; 
       FIG. 7  is a flowchart illustrating steps that are performed in a second energy saving mode; 
       FIG. 8  illustrates the interconnection between a MDIX configuration switch and a MDI configuration end station; 
       FIG. 9  illustrates a crossover interconnection between a MDIX configuration end station and a MDIX configuration switch; 
       FIG. 10  illustrates a crossover interconnection selector that may be implemented in a physical layer; and 
       FIG. 11  illustrates an embodiment of an energy saving scheme with crossover capability. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   Referring now to  FIG. 1 , a network  10  according to the prior art is connected to a plurality of network devices  12 - 1 ,  12 - 2 , . . . , and  12 - n . Each of the network devices  12 - 1 ,  12 - 2 , . . . , and  12 - n  includes a physical layer  14 - 1 ,  14 - 2 , . . . , and  14 - n , respectively, that is responsible for establishing and maintaining a communications link between the communicating network devices  12 . In situations where a single network device, such as network device  12 - 1 , is not connected to any other network devices, the network device  12 - 1  provides power to the physical layer  14 - 1  even though it is not presently communicating with any other network devices  12 . 
   Referring now to  FIG. 2 , a network device  20  according to the present invention includes a physical layer  22  and an energy saving circuit  24 . The energy saving circuit  24  can be implemented as a digital circuit, an analog circuit, a processor and software, an application specific integrated circuit (ASIC) or any other suitable circuit. In situations where the network device  20  is not connected to any other network devices, the energy saving circuit  24  reduces power consumption of the physical layer  22  as will be described more fully below. 
   Referring now to  FIGS. 3 ,  4  and  5 , the energy saving circuit  24  is connected to one or more physical layer circuits  26 , a receiver  28  and a transmitter  30 . The physical layer circuits  26  perform conventional functions of the physical layer other than the energy saving modes of the present invention. The energy saving circuit  24  enters a SENSE state when reset (steps  50  and  52 ). In the SENSE state, the physical layer  22  is powered down (step  52 ) except for the energy saving circuit  24  and the receiver  28 . The receiver  28  is preferably an Ethernet receiver such as a 10BASE-T receiver that draws very little power. 
   When connection activity exceeding a receiver threshold that is set by the receiver  28  or the sense circuit is detected (step  54 ), the energy saving circuit  24  moves into an ANEG state. In the ANEG state, the physical layer  22  is powered up (step  56 ) and a first timer (TIMER  1 ) is started (step  58 ). During autonegotiation, the physical layer  22  attempts to establish a connection (step  60 ) with other network devices  12 . The first timer TIMER 1  times out after a first predetermined period unless reset (step  62 ). While in the ANEG state, the first timer TIMER 1  is reset every time additional connection activity exceeding the receiver threshold is detected by the receiver  28  (step  64 ). 
   If the connection activity that was detected by the receiver  28  was a noise hit and there are no active network devices  12  that are connected to the network device  20 , the first timer TIMER 1  will eventually time out. In a preferred embodiment, the first predetermined period of the first timer TIMER 1  is set to approximately 1-5 seconds. When the first timer TIMER 1  times out, the energy saving circuit  24  returns to the SENSE state (step  52 ). If there is an active network device  12  attempting to establish communications, autonegotiation will complete (step  66 ) and the energy saving circuit  24  will enter a LINK state (step  70 ). In the LINK state, the physical layer  22  is powered up and operates normally. 
   If the physical layer  22  loses the connection (step  72 ), the physical layer  22  will move from the LINK state to the ANEG state and try to re-establish the connection (step  58 ). This method of control allows the physical layer  22  to automatically power up and down based on whether connection activity is present. As can be appreciated, energy is saved by powering down the physical layer  22  as described above. 
   Referring to  FIGS. 6 and 7 , a second energy saving mode of the energy saving circuit  24 - 1  of  FIG. 2  is shown. In the second energy saving mode, the physical layer  22 - 1  periodically transmits a single link pulse. A physical layer  22 - 1  with the second energy saving mode enabled can detect a link pulse from another physical layer  22 - 2  that has the second energy saving mode enabled. 
   The second power saving mode is initially enabled (step  100 ). A second timer TIMER 2  is started (steps  102  and  104 ). The second timer TIMER 2  times out after a second predetermined period. If the second energy saving mode is enabled and the second timer TIMER 2  times out (step  106 ), the energy saving circuit  24  moves into the PULSE state (step  108 ). In the PULSE state, the transmitter  30  is powered on and a link pulse is generated. Preferably a single link pulse is generated (step  110 ). After the single link pulse is generated, the energy saving circuit  24  returns to the SENSE state and the transmitter is shut down (step  112 ). 
   More power is consumed in the second energy saving mode than in the first energy saving mode because the transmitter link pulses are generated periodically. However, the link pulse transmission is preferably much less frequent than FLP bursts that are generated every 16 ms and that typically include 17 to 33 link pulses. For example, in the second energy saving mode a single link pulse can be generated once per second or at other intervals. 
   Some physical layers implement crossover functions. The first and second energy saving modes can be modified to work in conjunction with these crossover functions.  FIG. 8  shows the connection of transmit and receive pairs using an RJ-45 connector  120 . In a MDI configuration, an end station  122  is configured with pins  1  and  2  as a transmitter  126  and pins  3  and  6  as a receiver  128 . A switch  130  is configured with pins  1  and  2  as a receiver  132  and pins  3  and  6  as a transmitter  134 . A connection between the switch  130  and the end station  122  requires the connector  120  that provides a straight cable connection. However, the two switches in  FIG. 9  require a connection  140  that provides a crossover. Some physical layers employ a crossover interconnection selector inside of the physical layer as shown in  FIG. 10 . Depending on the cable that is used, the physical layer automatically detects and selects the correct pins to use by toggling switches  150 . The crossover function is defined more fully in IEEE 802.3, which is hereby incorporated by reference. In particular, Section 40.4.4-40.4.6 of IEEE 802.3 address the crossover capability. 
   Referring now to  FIG. 11 , an energy saving circuit  24 ′ with crossover capability is illustrated. The energy saving circuit  24 ′ is able to distinguish the source of the connection activity. In other words the energy saving circuit  24 ′ determines whether the connection activity is transmitted by the MDI receiver (pins  3  and  6 ) or by the MDIX receiver (pins  1  and  2 ). The energy saving circuit  24 ′ is operated in a manner that is similar to the energy saving circuit  24  that is illustrated in  FIG. 4 . However, the ANEG_MDI state or the ANEG_MDIX state are selected depending on the source of the connection activity. In the case of ANEG_MDI and LINK_MDI, the physical layer  22 ′ operates in the MDI configuration. In the case of ANEG_MDIX and LINK_MDIX, the physical layer  22 ′ operates in the MDIX configuration. 
   In the second energy savings mode, the physical layer  22 ′ randomly selects the MDI or MDIX configuration and transmits the link pulse on the appropriate ports. If the MDI configuration is selected, the energy saving circuit  24 ′ enters a PULSE_MDI state and generates a link pulse on the MDI transmitter (pins  1 ,  2 ). If the MDIX configuration is selected, the energy saving circuit  24 ′ enters a PULSE_MDIX state and generates a link pulse on the MDIX transmitter (pins  1 ,  2 ). If two devices implement the auto crossover function and the second energy saving mode, the random generation of link pulses in the MDI and MDIX configurations will eventually allow each device to recognize the activity of the other device. 
   Preferably an interrupt signal is generated whenever the physical layer  22 ′ transitions between the SENSE and ANEG states. The interrupt signal is used to shut down additional circuitry, such as an Ethernet controller, while the physical layer  22 ′ is in the SENSE state. Shutting down the additional circuitry permits the energy saving circuit  24 ′ to save additional power. Once the physical layer  22 ′ goes into the ANEG state, the interrupt signal is generated to let the energy saving circuit  24 ′ know that it needs to power up. Similarly, when the physical layer  22 ′ transitions from the ANEG state to the SENSE state, an interrupt signal is generated to let the physical layer  22 ′ know that it should power down. 
   Thus it will be appreciated from the above, the present invention discloses an energy saving circuit and method for providing energy savings for Ethernet transceivers. It will be equally apparent and is contemplated that modification and/or changes may be made in the illustrated embodiment without departure from the invention. Accordingly, it is expressly intended that the foregoing description and accompanying drawings are illustrative of preferred embodiments only, not limiting, and that the true spirit and scope of the present invention will be determined by reference to the appended claims and their legal equivalent.