Electrical computers and digital processing systems: support – Computer power control – Power conservation
Reexamination Certificate
2000-07-31
2004-07-06
Lee, Thomas (Department: 2116)
Electrical computers and digital processing systems: support
Computer power control
Power conservation
C713S300000, C713S310000, C713S002000, C713S323000, C713S324000, C713S330000, C713S340000
Reexamination Certificate
active
06760850
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to remotely waking a computer that is in an off state. More particularly, it relates to power management methods for selectively enabling a computer wakeup device in response to the presence or removal of AC power.
2. Background of the Invention
Generally stated, the term “power management” refers to the ability of a computer system to conserve or otherwise manage the power that it consumes. Many personal computer systems conserve energy by operating in special low-power modes when the user is not actively using the system. Although used in desktop and portable systems alike, these reduced-power modes particularly benefit laptop and notebook computers by extending the battery life of these systems. Some computer systems automatically enter low-power mode when a user has not performed a certain action within a given period of time. For example, the computer might power down the monitor if the video display has not recently changed or may power down the hard drive if the user has not recently opened or saved any files onto the hard disk. If the computer detects a period of inactivity, the computer may enter a “deep sleep” mode in which power is completely cut off to all but a few devices within the computer. In addition, the user often can initiate the sleep mode through a menu in the operating system (OS) or by pressing a power button on the computer. Typically the memory contents are preserved so that the computer returns to the same state that it was in when the sleep mode began.
There are many ways that have been used to implement an energy-conserving, reduced-power mode. Examples include hard off (power is disconnected), soft off (power is supplied only to components which monitor activity external to the system), hibernated power state (contents of memory are stored on disk and current state of computer is preserved while power consumption is reduced to a minimum level), suspend mode (all central processor activities are halted, but power to memory is maintained and dynamic RAM is refreshed), and sleep mode (the clock signal is reduced or halted to some or all of the system components during periods of inactivity). The sleep and suspend modes may each be invoked at various levels, depending on the particular implementation of these modes, and recovery from these modes is implementation specific.
Although these reduced-power modes may render the computer temporarily or partially inoperable, the user can generally restore full-power, or “wake up” the computer, at any time. For example, the computer may automatically restore video power if the user moves the mouse or presses a key on the keyboard, or might power up the hard disk if the user attempts to open or save a file. The source of the triggering activity may come from a local mechanism (i.e. a switch or sensor of any kind such as a power switch, a reset switch, a pressable key, a pressure sensor, a mouse, a joystick, a touch pad, a microphone, or a motion sensor), or the trigger source may be remote. In addition, some computers have the capability to wake automatically in response to incoming phone calls detected by a modem or to wakeup messages received over a local area network (LAN). Sleep mode is often an attractive alternative to completely shutting the computer down, because the computer consumes little power during sleep mode and because waking up from sleep mode typically is much faster than rebooting the system.
Early implementations of the various power modes required the computer hardware itself to monitor user activity and determine the proper power state for each device in the computer system. These early computer systems included a read only memory (ROM) device that stored a set of instructions for the computer to follow in order to carry out power management functions. The set of instructions formed part of the Basic Input/Output System (BIOS) of the computer, which also included instructions for procedures such as accessing data on a hard or floppy disk drive and controlling the graphics display. The ROM device containing the BIOS is referred to as the “BIOS ROM”. Because hardware-based power management instructions usually are included in BIOS, such a management scheme is commonly known as “BIOS power management”. Under BIOS power management, conditions within the computer system that initiate power state transitions, such as button presses and periods of inactivity explained above, generate system management interrupt (SMI) signals to the central processing unit (CPU). Upon receiving an SMI, the CPU executes the BIOS power management instructions stored in ROM to change the power state.
More recently, the Advanced Configuration and Power Interface (ACPI) specification, written collaboratively by Intel, Microsoft, and Toshiba, has introduced the concept of managing power functions using the computer's operating system software (e.g., Windows® 98 and Windows® NT). Centralizing power management within the operating system, in contrast with earlier hardware-based power management techniques, allows computer manufacturers to make simpler, less expensive hardware components that do not have to manage their own power states. Instead, these devices need only to respond to power management commands from the operating system. In general, operating system-based power management enables the computer system to implement relatively complex power management procedures that may have been difficult, if not impossible, to realize using a more decentralized, hardware-based approach. In fact, implementing power control through ACPI instead of through traditional hardware methods can significantly reduce the power consumption of some computer systems. Operating system-based power management also provides the user with some level of power management control.
Under ACPI, a computer system can be placed in one of six graduated reduced-power system states, which do not necessarily correspond (in functionality or in name) to the power down modes recited above. The six system power states, S
0
, S
1
, S
2
, S
3
, S
4
, and S
5
encompass varying levels of system activity ranging from fully operational (S
0
) to “soft off” (S
5
). Power states S
1
-S
5
represent sleeping states in which the computer system is neither fully operational nor completely powered off. The sleep states generally encompass varying levels of system activity (or “context”) and require different lengths of time (or “wakeup latencies”) to return to full power. The S
1
, S
2
, and S
3
states may be referred to as Suspend states. In all three cases, the system DRAM retains valid information including application status, OS status, and hardware context that is lost during Suspend. Because sleep state S
5
represents the deepest sleep state, it may also be referred to equivalently as the “off” state or as the lowest-power state.
In both the S
4
and S
5
states, the CPU and its DRAM memory hold no valid information. Additionally, all power is expected to be removed from the system except for a small amount of logic that may respond to events such as actuation of a power button. The S
4
and S
5
states are electrically identical. The difference between these states lies in the source of CPU memory during wakeup. In S
4
, which may be referred to as the Hibernation state to distinguish it from the S
5
Off state, the previous state of the CPU's memory has been stored to the hard drive. A transition back the S
0
working state from the S
4
hibernation state causes the CPU to load this memory from the hard drive and the operating system will resume the state it was in prior to entering the S
4
hibernation state. The S
5
OFF state, on the other hand, presumes the user will load the operating system into CPU memory from a completely uninitialized state.
Transitioning between the system power states generally requires cooperat
Atkinson Lee W.
Dunn Loren S.
Lakdawala Rahul V.
Massey Paul G.
Hewlett--Packard Development Company, L.P.
Lee Thomas
Trujillo James K
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