# Patent

## Title
Low power mode for a network interface

## Abstract

A network interface including: a medium access control device configured to operate at a first power state during an inactive power mode, and operate at a second power state during an active power mode; a physical layer device including (i) an energy detect module configured to detect energy on a medium during the inactive power mode, and (ii) an energy save module configured to time a first pre-determined period subsequent to the energy detect module detecting energy on the medium. The medium access control device is further configured to, subsequent to the energy detect module detecting energy on the medium, transition to the second power state of the active power mode, and communication with the medium access control device via the medium is enabled subsequent to expiration of the first pre-determined period.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 12/157,239 (Now U.S. Pat. No. 7,937,600), filed Jun. 9, 2008, which is a continuation of U.S. application Ser. No. 11/114,402 (Now U.S. Pat. No. 7,392,412), filed Apr. 26, 2005, which is a continuation-in-part of U.S. application Ser. No. 09/990,137 (Now U.S. Pat. No. 6,993,667), filed Nov. 21, 2001, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/256,117, filed Dec. 15, 2000. The disclosures of the above applications are incorporated herein by reference in their entirety.


TECHNICAL FIELD
The present invention relates to network devices, and more particularly to energy saving modules for network devices.
BACKGROUND
Referring now to FIG. 1, host devices 10, such as computers, personal digital assistants (PDA's) and/or network enabled devices and/or appliances, commonly include a network interface 12 for communicating with other hosts or link partners over a medium. The network interface 12 draws power from a power source associated with the host device 10.
Referring now to FIG. 2, the network interface 12 typically includes a host interface 14 that provides an interface to the host device 10. A MAC device/buffer 18 includes logic that bridges a physical layer (PHY) device 20 and the host interface 14. The PHY device 20 communicates with a wired or wireless medium 21. In some implementations, the host interface 14 is compatible with a peripheral component interconnect (PCI) and/or PCI-Express (PCI-E) protocols. A regulator module 22 may be provided that receives a first voltage level from the host device 10 and converts the first voltage level to a second voltage level for use in the network interface 12.
The power that is dissipated by the network interface 12 tends to cause undesirable heat generation. For portable host devices 10, the power consumption of the network interface 12 also tends to reduce battery life of the host device 10.
SUMMARY
In general, in one aspect, this specification describes a network interface including: a medium access control device configured to operate at a first power state during an inactive power mode, and operate at a second power state during an active power mode; a physical layer device including (i) an energy detect module configured to detect energy on a medium during the inactive power mode, and (ii) an energy save module configured to time a first pre-determined period subsequent to the energy detect module detecting energy on the medium. The medium access control device is further configured to, subsequent to the energy detect module detecting energy on the medium, transition to the second power state of the active power mode, and communication with the medium access control device via the medium is enabled subsequent to expiration of the first pre-determined period.
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 is a functional block diagram of host device and network interface according to the prior art;
FIG. 2 is a functional block diagram of the network interface of FIG. 1 in further detail;
FIG. 3 is a functional block diagram of a network interface;
FIG. 4 is a functional block diagram of a network interface according to the present invention;
FIG. 5 is a state diagram of power management for a physical layer (PHY) device; and
FIG. 6 is a state diagram of power management for a medium access control (MAC) device and a host interface.



DETAILED DESCRIPTION
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. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module and/or device refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. For purposes of clarity, the same reference numerals will be used to identify similar elements. References to logical one, true, and on are equivalent to each other, and references to logical zero, false, and off are equivalent to each other, unless otherwise noted. Parts or all of the invention may also be implemented with equivalent embodiments using logic that is inverted from that disclosed.
Referring now to FIG. 3, a block diagram of a network interface 23 is shown. A regulator module 24 has a power input 26 that receives power from the host device 10. A plurality of regulator module outputs 28-1, 28-2, 28-3, and 28-4 (collectively regulator module outputs 28) provide power to other modules of the network interface 12. A host interface 30 provides bidirectional communication with the host device 10.
A physical layer (PHY) device 34 includes an energy savings module (ESM) 36 and other PHY device modules 38. The ESM 36 has an output 40 that switches at least some of the PHY device modules 38 between active and inactive power modes depending upon link status and activity. A medium access control (MAC) device 44 communicates with the host device 10 through the host interface 30. The MAC device 44 also communicates with the PHY device 34 and receives a link status signal 46 indicating the presence or absence of a link.
Referring now to FIG. 4, an improved network interface 50 is shown connected to the host device 10. A regulator module 52 has a power input 54 that receives power from the host device 10. A clock module 55 generates at least first and second clock signals. The first or lower clock signal may be used to supply low voltage logic running during the inactive mode. The second or higher clock signal may be used during the active mode for higher speed logic. The clock module 55 may include a clock generator, a phase-locked loop (PLL), an oscillator and/or any other circuit to generate the two clock signals. To simplify FIG. 4, skilled artisans will appreciate that individual connections from the clock module 55 to components in the network interface are present but not shown.
The regulator module 52 has a plurality of regulator module outputs 56-1, 56-2, 56-3, and 56-4 that are referred to collectively as the regulator module outputs 56. The regulator module outputs 56-1, 56-2, 56-3 and 56-4 provide power to a PHY device 66, a MAC device 62, and a host interface 64, respectively.
The PHY device 66, the MAC device 62, and the host interface 64 include one or more analog and/or digital modules. Analog modules can be powered during the active mode and either powered or not powered (0 volts) during the inactive mode. Analog modules that are not powered typically require settling time when transitioning back to the active mode. Digital modules can be powered at a second or higher voltage level during the active mode. Digital modules can be powered at a first or lower voltage level during the inactive mode to maintain logic states. Digital modules can receive a higher clock signal during the active mode and a lower clock signal (for logic that runs during the inactive mode) or no clock signal during the inactive mode.
One or more of the regulator module outputs 56 are individually switchable between two or more output voltages. In a some implementations, the regulator module outputs 56 are switchable between two non-zero voltages. The first voltage is selected to be sufficient to place the host interface 64 and the MAC device 62 in a standby condition to retain data. The second voltage is greater than the first voltage and is selected to allow the host interface 64, the MAC device 62, and a PHY device 66 to be fully operational. The PHY device 66 communicates with a medium 67. For analog modules that are not powered, a third voltage or ground can be provided and/or a switched ground connection. A voltage selection signal 68 determines whether the first voltage or the second voltage is applied by each of the regulator module outputs 56 as will be described below.
The MAC device 62, which may contain a data buffer, is in bidirectional communication with the host interface 64 and the PHY device 66. The PHY device 66 selectively negotiates link parameters of a link. A link status signal 78 from the PHY device 66 provides the MAC device 62 with an indication of whether the PHY device 66 has established a link.
The ESM 58 includes one or more timers 82 and generates an energy signal that is used to indicate operational states of the network interface 50. A first timer TMR1 is reset when energy exceeding a predetermined threshold is detected by an energy detect module 76. TMR1 is used to limit the amount of time that the PHY device 66 attempts to establish a link after activity is detected and is subsequently not detected. When the link is lost, the PHY device 66 is powered down and the ESM 58 and the energy detect module 76 remain powered and monitor the medium for activity. When activity is detected, the PHY device 66 is powered up, TMR1 is reset and the PHY device 66 attempts to establish a link. If the TMR1 times out before a link is established, the PHY device 66 returns to the inactive mode.
The energy detect module 76 may be implemented by a low power comparator, which compares signals on the medium 67 to a threshold. The energy detect module 76 may alternatively include a digital input that is driven by an optics module that determines when a sufficient amount of optical energy is received. In some implementations, the PHY device 66 indicates link status. In some implementations, the PHY device 66 may include an autonegotiation module that negotiates link parameters and indicates link status, although the PHY device 66 need not include an autonegotiation module and/or be capable of autonegotiation.
A second timer TMR2 is used by the PHY device 66 to periodically transition the inactive PHY device to active mode and transmit pulses such as link pulses. If two network devices or link partners have power save functionality, both devices may remain inactive for an indefinite period while listening for activity. Therefore, even if activity is not detected, the PHY device 66 is periodically powered up when TMR2 times out and link pulses are sent. Upon receiving the link pulses, a link partner will detect activity, exit the inactive mode and attempt to establish a link.
Additional timers TMR3 and TMR4 are used to track time after state changes, which are described later herein, to provide settling times between selected state changes and/or sufficient time to complete processes. An energy signal provides an indication that a receive signal exceeds a threshold. The ESM 58 also generates the voltage selection signal 68.
Referring now to FIG. 5, a state diagram 90 of the PHY device 66 is shown. Upon receiving a reset signal 92, the regulator module outputs 56 are set to the first voltage and the PHY device 66 enters an ENERGY_DETECT state 94. The ESM 58 sets the energy signal to false, thereby indicating that the PHY device 66 is waiting for activity on the medium. The PHY device 66 remains in a low power condition. TMR2 is started. When TMR2 expires, the PHY device 66 changes to a PULSE state 95. In the PULSE states, TMR5 is started, energy=0 and the PHY sends a pulse. If a signal is not detected, the PHY device transitions to a LINE_ACTIVE state 96. Alternatively, if TMR5 expires, the PHY returns to the ENERGY_DETECT state 94. TMR5 expires when the pulse is detected. When the energy detect module 76 detects activity as described above, the PHY device 66 changes to a LINE_ACTIVE state 96.
In the LINE_ACTIVE state 96, the ESM 58 changes the energy signal from false to true, indicating that activity has been detected. The receive signal starts TMR1. The false to true transition of the energy signal causes the ESM 58 to switch the regulator module outputs 56 to the second voltage. The PHY device 66 also attempts to establish a communication link. When the PHY device 66 establishes the communication link, as indicated by the link status signal 78, it leaves the LINE_ACTIVE state 96 and enters a LINK_UP state 98.
In the LINK_UP state 98, the energy signal remains true. The PHY device 66 remains in the LINK_UP state 98 until it loses the communication link as indicated by the link status signal 78 changing from true to false. Upon losing the communication link the PHY device 66 leaves the LINK_UP state 98 and enters a POWERING_DOWN state 100.
In the POWERING_DOWN state 100, the PHY device 66 starts TMR4 and changes the energy signal from true to false. The MAC device 62 responds to the link status signal 78 becoming false by preparing for the regulator module output 56-3 to return to the first voltage. TMR4 expires after a predetermined time, which may be different from the predetermined time the PHY device returns to the ENERGY_DETECT state.
Discussion will now return to the LINE_ACTIVE state 96. If the receive signal activity ceases and TMR1 expires before the PHY device 66 establishes the communication link, the PHY device 66 will change to the POWERING_DOWN state 100.
Referring now to FIG. 6, a state diagram 102 of the MAC device 62 and the host interface 64 is shown. Upon receiving the reset signal 92, the regulator module outputs 56 are set to the first voltage and the MAC device 62 and the host interface 64 enter a LOW_VOLTAGE state 104. The LOW_VOLTAGE state 104 allows the MAC device 62 and the host interface 64 to have lower leakage currents than when the regulator module outputs 56 are at the second voltage. When the energy signal 88 changes from false to true and/or link status changes to false, the ESM 58 increases the regulator module outputs 56-3 and 56-4 to the second voltage, thereby changing the MAC device 62 and the host interface 64 to a NORMAL_VOLTAGE state 106.
Upon entering the NORMAL_VOLTAGE state 106, the MAC device 62 and the host interface 64 are provided time to stabilize from the voltage increase TMR3 is also started. When TMR3 expires, the MAC device 62 and the host interface 64 change to a POWER_UP state 108.
In the POWER_UP state 108, the MAC device 62 and the host interface 64 are fully operational and the regulator module outputs 56 are at the second voltage. The MAC device 62 and the host interface 64 remain in the POWER_UP state 108 until the link status signal 78 changes from true to false. Upon link status signal 78 being changed, the MAC device 62 and the host interface 64 change to a POWER_DOWN state 110.
Upon entering the POWER_DOWN state 110, the MAC device 62 and the host interface 64 begin preparing for the regulator module lines 56-3 and 56-4 to return to the first voltage. For example, the MAC device 62 may prepare by emptying its buffer if so equipped, or by preparing other internal registers for the voltage change. TMR6 is started. Upon expiration of TMR6, the ESM 58 switches the regulator module outputs 56, thereby returning the MAC device 62 and the host interface 64 to the LOW_VOLTAGE state 104.
Returning now to the NORMAL_VOLTAGE state 94. If the PHY device 66 changes the energy signal 88 from true to false, then the MAC device 62 and the host interface 64 will transition to from the NORMAL_VOLTAGE state 106 directly to the POWER_DOWN state 110.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.

## Claims

1. A network interface, comprising:
a medium access control device configured to
operate at a first power state during an inactive power mode, and
operate at a second power state during an active power mode;

a physical layer device in communication with each of the medium access control device and a medium, wherein the physical layer device includes
an energy detect module configured to detect energy on the medium during the inactive power mode; and

an energy save module configured to time a first pre-determined period subsequent to the energy detect module detecting energy on the medium,
wherein the medium access control device is further configured to, subsequent to the energy detect module detecting energy on the medium, transition to the second power state of the active power mode, and
wherein communication with the medium access control device via the medium is enabled subsequent to expiration of the first pre-determined period.

2. The network interface of claim 1, wherein, in response to a link being lost on the medium:
the medium access control device is configured to transition from the second power state of the active power mode to the first power state of the inactive mode;
the energy save module is configured to time a second pre-determined period; and
the energy detect module is configured to detect activity on the medium subsequent to expiration of the second pre-determined period.

3. The network interface of claim 1, further comprising:
a clock module configured to generate a clock signal,
wherein the medium access control device includes a digital module configured to (i) receive the clock signal during the active power mode and (ii) not receive the clock signal during the inactive power mode.

4. The network interface of claim 1, further comprising:
a clock module configured to generate a clock signal,
wherein the physical layer device includes a digital module configured to (i) receive the clock signal during the active power mode and (ii) not receive the clock signal during the inactive power mode.

5. The network interface of claim 1, further comprising a host interface in communication with the medium access control device.

6. The network interface of claim 5, wherein the host interface is compatible with a peripheral component interconnect (PCI) protocol.

7. The network interface of claim 5, wherein the host interface is compatible with a peripheral component interconnect express (PCI-Express) protocol.

8. A host device comprising the network interface of claim 1.

9. The host device of claim 8, wherein the host device comprises a computer or a personal digital assistant.