Portable computer with adaptive demand-driven power management

• US 5,954,820 A
• Filed: 09/26/1997
• Issued: 09/21/1999
• Est. Priority Date: 09/26/1997
• Status: Expired due to Fees

• Current Assignee: Lenovo Singapore Pte Limited (Lenovo Group Ltd.)
• Original Assignee: International Business Machines Corporation
• Inventors: Hetzler, Steven Robert
• Primary Examiner(s): AUVE, GLENN ALLEN
• Application Number:
  US08/939,110
• Time in Patent Office: 725 Days
• Field of Search: 395/750.03, 395/750.05, 395/750.06
• US Class Current: 713/323
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A method for managing power in a portable computer uses past access history of the various electrically-powered computer components and a prediction of future user demands to determine power-save mode entry and exit conditions. The component or the computer system keeps track of the access patterns. In the case of the display system component, such as the LCD display panel, because the access occurs when the user is watching the display panel and is thus not possible to measure directly, the accesses are measured indirectly from keyboard and/or pointing device activity. Each component access is detected and used to compute a current access frequency. The current access frequency is compared to a previously calculated and continuously updated threshold frequency. The threshold frequency is representative of the access pattern, e.g., uniform or sporadic, and is computed from equations that include adjustable gain factors. During operation of the component the appropriate power-save mode is entered when the current access frequency falls below the threshold frequency. The component can also adapt dynamically to varying workload situations, thereby saving more energy without degrading performance. This is accomplished by adjusting the gain factors parameters in response to tracking the actual performance of the system, thereby changing the threshold frequency. The component also determines when to exit a power-save mode without necessarily waiting for a user access.

Claims

1. A method of managing electrical power usage in a computer having a plurality of electrically powered components that are accessed for operation within the computer, the components including a central processing unit (CPU), a bus connecting the CPU to other components, memory accessible by the CPU, a keyboard and a keyboard controller that communicates keystrokes from the keyboard to the bus, at least one of the electrically powered components requiring a first level of electrical power when accessed for full operation and being capable of less than full operation in at least one reduced-power mode, and wherein an access to said at least one component when said at least one component is in said reduced-power mode requires recovery from said reduced-power mode, the method comprising:

determining the frequency of accesses to said at least one component that require full operation at said first level of electrical power;

storing a plurality of values representing a like plurality of previously determined access frequencies;

computing, from the stored values of previously determined access frequencies, an access threshold frequency; and

reducing electrical power to said at least one component when the determined access frequency falls below the computed access threshold frequency to cause said at least one component to enter said reduced-power mode.

2. The method according to claim 1 further comprising restoring power to the previously power-reduced component in response to an access.

3. The method according to claim 1 wherein determining the frequency of accesses comprises estimating the access frequency from the number of accesses occurring in a predetermined time window.

4. The method according to claim 1 wherein computing an access threshold frequency from previously determined access frequencies comprises first determining if the standard deviation of said plurality of stored values is less than a predetermined fraction of the mean of said plurality of stored values, and thereafter multiplying the standard deviation by a gain factor and subtracting the product of said multiplication from the mean.

5. The method according to claim 1 wherein computing an access threshold frequency from previously determined access frequencies comprises first determining if the standard deviation of said plurality of stored values is greater than a predetermined fraction of the mean of said plurality of stored values, and thereafter multiplying the stored value representing the minimum access frequency in the plurality of stored values by a gain factor.

6. The method according to claim 1 wherein computing an access threshold frequency comprises computing an access threshold frequency from the maximum and minimum access frequencies in a set of previously determined access frequencies.

7. The method according to claim 6 wherein computing an access threshold frequency includes multiplying the maximum and minimum access frequencies by a predetermined gain factor.

8. The method according to claim 7 further comprising adjusting the gain factor.

9. The method according to claim 1 further comprising determining if the accesses are a periodic pattern and thereafter restoring power to the power-reduced component prior to the next periodic access.

10. The method according to claim 1 wherein determining the frequency of accesses to said at least one electrically powered component comprises indirectly determining the frequency of accesses.

11. The method according to claim 1 wherein said at least one electrically powered component is a display, and wherein determining the frequency of accesses to the display comprises indirectly determining the frequency of accesses to the display by determining, from the keyboard controller, the frequency of accesses to the keyboard.

12. The method according to claim 11 wherein determining the frequency of accesses to the keyboard comprises using the keyboard controller to count the number of keystrokes occurring in a predetermined time window and wherein storing the plurality of values comprises storing the count in memory.

13. The method according to claim 11 wherein the display includes a panel and a backlight and wherein reducing electrical power to the display comprises removing power to the panel and backlight.

14. The method according to claim 1 wherein said at least one electrically powered component is a display having a display panel, wherein the computer includes a stylus for contacting the display panel and a stylus controller, and wherein determining the frequency of accesses to the display comprises indirectly determining the frequency of accesses to the display by determining, from the stylus controller, the frequency of accesses to the stylus.

15. The method according to claim 1 wherein said at least one electrically powered component is the CPU, and wherein reducing electrical power to the CPU comprises causing the CPU to operate at a clock rate slower than the clock rate at full operation of the CPU.

16. The method according to claim 1 wherein said at least one component is an optical disk drive that includes an optical disk, a spindle motor for rotating the disk, a head for reading data from the disk, an actuator connected to the head for moving the head to different tracks on the disk, and servo control electronics coupled to the actuator for maintaining the head on the tracks of the disk, and wherein determining the frequency of accesses comprises determining the frequency of accesses causing the head to read data from the disk, and wherein reducing power comprises moving the actuator to a parking location and reducing power to the servo control electronics.

17. The method according to claim 1 wherein said at least one component is an optical disk drive that includes an optical disk, a spindle motor for rotating the disk, a head for reading data from the disk, an actuator connected to the head for moving the head to different tracks on the disk, and servo control electronics coupled to the actuator for maintaining the head on the tracks of the disk, and wherein determining the frequency of accesses comprises determining the frequency of accesses causing the actuator to seek across the disk, and wherein reducing power comprises moving the actuator to a parking location and shutting off the spindle motor.

18. A method of managing electrical power usage in a portable computer having a display system including a display panel viewable by a computer user, a central processing unit (CPU), a memory accessible by the CPU, a bus connecting the CPU to the display system, a keyboard, and a keyboard controller that communicates keystrokes made by the computer user from the keyboard to the bus, the method comprising:

determining the frequency of keystrokes, said determined frequency representing the frequency at which the display panel is viewed by computer user;

storing in memory a plurality of values representing a like plurality of previously determined keystroke frequencies;

computing, from the stored values of previously determined keystroke frequencies, a display panel viewing threshold frequency; and

removing power to the display panel when the determined keystroke frequency falls below the computed display panel viewing threshold frequency.

19. The method according to claim 18 wherein determining the frequency of keystrokes comprises estimating the keystroke frequency from the number of keystrokes occurring in a predetermined time window.

20. The method according to claim 18 further comprising restoring power to the display panel in response to a keystroke.

21. The method according to claim 18 wherein the display system is a liquid crystal device (LCD) display system.

22. The method according to claim 21 wherein the LCD display system includes a LCD backlight, and further comprising removing power to the backlight when the determined keystroke frequency falls below the computed display panel access threshold frequency.

23. The method according to claim 18 wherein the computer includes a pointing device coupled to the keyboard controller for addressing the display panel, and wherein determining the frequency of keystrokes includes determining the frequency of uses of the pointing device.

24. A method of managing electrical power usage in a computer having a plurality of electrically powered components that are accessed for operation within the computer, the components including a central processing unit (CPU), a bus connecting the CPU to other components, memory accessible by the CPU, a keyboard and a keyboard controller that communicates keystrokes from the keyboard to the bus, at least one of the electrically powered components requiring a first level of electrical power when accessed for full operation and being capable of entering a power-save mode of operation and exiting said power-save mode to return to full operation, and wherein an access to said at least one component when said at least one component is in said power-save mode requires recovery from said power-save mode, the method comprising the steps of:

determining the frequency of accesses to said at least one component that require full operation at said first level of electrical power;

storing a plurality of values representing a like plurality of previously determined access frequencies;

computing, from the stored values of previously determined access frequencies, a first access threshold frequency;

entering the power-save mode when the determined access frequency is less than the computed first access threshold frequency;

selecting a performance factor having a range of values, one limit of the range representing maximum power savings for said at least one component and the other limit of the range representing maximum performance for said at least one component; and

using the selected performance factor to modify the first access threshold frequency computation, whereby the power-save mode entry behavior of said at least one component is adjusted by the selected performance factor.

25. The method according to claim 24 wherein the step of computing the first access threshold frequency includes use of a gain factor.

26. The method according to claim 25 wherein the step of using the selected performance factor to modify the first access threshold frequency computation comprises adjusting the gain factor by multiplying it by the selected performance factor.

27. The method according to claim 24 wherein said at least one component is capable of entering and exiting a second power-save mode of operation having power usage less than the first power-save mode, and further comprising the steps of:

computing from the stored values of previously determined access frequencies a second access threshold frequency different from said computed first access threshold freguency;

entering the second power-save mode when the determined access frequency is less than the computed second access threshold frequency; and

using the selected performance factor to modify the second access threshold frequency computation, whereby the second power-save mode entry behavior of said at least one component is adjusted by the selected performance factor.

28. The method according to claim 27 further comprising causing said at least one component to enter the second power-save mode without first entering the first power-save mode.

29. The method according to claim 24 further comprising determining if the stored values of access frequencies represent a pattern of periodic accesses and thereafter exiting the power-save mode prior to the next periodic access.

30. A method of managing electrical power usage in a computer having a plurality of electrically powered components that are accessed for operation within the computer, the components including a central processing unit (CPU), a bus connecting the CPU to other components, memory accessible by the CPU, a keyboard and a keyboard controller that communicates keystrokes from the keyboard to the bus, at least one of the electrically powered components requiring a first level of electrical power when accessed for full operation and being capable of entering a power-save mode of operation and exiting said power-save mode to return to full operation, and wherein an access to said at least one component when said at least one component is in said power-save mode requires recovery from said power-save mode, the method comprising the steps of:

determining the frequency of accesses to said at least one component that require full operation at said first level of electrical power;

storing a plurality of values representing a like plurality of previously determined access frequencies;

computing, from the stored values of previously determined access frequencies, an access threshold frequency;

when the access frequency is less than the access threshold frequency, entering the power-save mode of operation;

detecting the power-save mode entrances and exits;

computing the durations of power-save modes from the detected mode entrances and exits;

computing an energy penalty if a computed power-save mode duration is less than a predetermined energy break-even time, said break-even time being the power-save mode duration required for the energy savings of said at least one component to be generally equal to the energy required for said at least one component to exit the power-save mode;

accumulating the computed energy penalties; and

modifying the access threshold frequency when the accumulated energy penalties exceed a predetermined trip level, whereby the power-save mode entry behavior of said at least one component is dynamically adjusted from the accumulated computed energy penalties.

31. The method according to claim 30 wherein determining the freguency of accesses comprises detecting the accesses, and further comprising:

computing a missed opportunity penalty if the time interval between successive detected accesses without power-save mode entry is greater than said energy break-even time;

accumulating the computed missed opportunity penalties; and

modifying the access threshold frequency when the accumulated missed opportunity penalties exceed a predetermined trip level, whereby the power-save mode entry behavior of said at least one component is dynamically adjusted from the accumulated computed missed opportunity penalties.