Apparatus for reducing computer system power consumption

• US 6,029,249 A
• Filed: 12/13/1993
• Issued: 02/22/2000
• Est. Priority Date: 12/17/1991
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: Atkinson, Lee Warren
• Primary Examiner(s): Hafiz, Tariq R.
• Application Number:
  US08/166,609
• Time in Patent Office: 2,262 Days
• Field of Search: 395/750, 395/550, 364/200, 364/900, 364/707, 364/492, 365/226, 365/227
• 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: G06F 1/3215 Monitoring of peripheral devices
• CPC Class Codes: G06F 11/3409 for performance assessment
• CPC Class Codes: G06F 11/3423 where the assessed time is active or idle time
• CPC Class Codes: G06F 12/0802 Addressing of a memory level in which the access to the desired data or data block requires associative addressing means, e.g. caches
• CPC Class Codes: G06F 2201/86 Event-based monitoring
• CPC Class Codes: G06F 2201/88 Monitoring involving counting
• CPC Class Codes: G06F 2201/885 Monitoring specific for caches
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A battery powered computer system determines when the system is not in use by monitoring various events associated with the operation of the system. The system preferably monitors the number of cache read misses and write operations, i.e., the cache hit rate, and reduces the system clock frequency when the cache hit rate rises above a certain level. When the cache hit rate is above a certain level, then it can be assumed that the processor is executing a tight loop, such as when the processor is waiting for a key to be pressed and then the frequency can be reduced without affecting system performance. Alternatively, the apparatus monitors the occurrence of memory page misses, I/O write cycles or other events to determine the level of activity of the computer system.

Claims

1. An apparatus for use with a computer system for reducing power consumption of the computer system, comprising:

a processor having a clocking input;

memory coupled to said processor;

means for producing a clocking signal having a frequency;

a counter coupled to said processor for counting a number of events indicative of activity of the computer system during a preset period of activity of said processor;

means coupled to said counter for periodically reading the number of events counted by said counter;

means coupled to said periodic reading means and said clocking signal producing means for adjusting the frequency of the clocking signal based on the counted number of events; and

means coupled to said adjusting means for outputting the frequency adjusted clocking signal to said processor clocking input.

2. The apparatus of claim 1, further comprising:

means coupled to said adjusting means for determining the current operating frequency of said clocking signal; and

wherein said adjusting means further adjusts the frequency of said clocking signal based on said current operating frequency of said clocking signal.

3. The apparatus of claim 1, wherein said adjusting means includes:

means for determining if said clocking signal is operating at a higher or a lower frequency;

means coupled to said periodic reading means for determining if said counted number of events is greater than a first value if said clocking signal is operating at said lower frequency;

means coupled to said greater than determining means and said clocking signal producing means for increasing the frequency of said clocking signal if said counted number of events is greater than said first value and said clocking signal is operating at said lower frequency;

means coupled to said periodic reading means for determining if said counted number of events is less than a second value if said clocking signal is operating at said higher frequency; and

means coupled to said less than determining means and said clocking signal producing means for decreasing the frequency of said clocking signal if said counted number of events is less than said second value and said clocking signal is operating at said higher frequency.

4. The apparatus of claim 3, wherein said first value is equal to said second value.

5. The apparatus of claim 1, further comprising:

cache memory coupled to said processor; and

wherein said counter comprises means for counting cache read miss operations and memory write operations during a preset period of time of activity of said processor.

6. The apparatus of claim 1, wherein said memory is organized in pages, the apparatus further comprising:

cache memory coupled to said processor;

input/output devices coupled to said processor; and

wherein said counter comprises means for counting events selected from the group consisting of cache miss and memory write operations, memory page miss operations, and input/output write operations during a preset period of time of activity of said processor.

7. A method for reducing power consumption of a computer system, the system including a processor and a clocking signal producer having a clocking signal frequency, comprising the steps of:

counting a number of events indicative of the activity level of the computer system during a preset period;

periodically determining counted number of events;

adjusting the frequency of the clocking signal from the clocking signal producer based on the counted number of events; and

outputting the frequency adjusted clocking signal to the processor.

8. The method of claim 7, further comprising:

determining the current operating frequency of the clocking signal; and

wherein said step of adjusting further comprises adjusting the frequency of the clocking signal based on said current operating frequency of the clocking signal.

9. The method of claim 7, wherein said step of adjusting includes:

determining if the clocking signal is operating at a higher or lower frequency;

determining if said counted number of events is greater than a first value if the clocking signal is operating at said lower frequency;

increasing the frequency of the clocking signal if said counted number of events is greater than said first value and the clocking signal is operating at said lower frequency;

determining if said counted number of events is less than a second value if the clocking signal is operating at said higher frequency; and

decreasing the frequency of said clocking signal if said counted number of events is less than said second value and the clocking signal is operating at said higher frequency.

10. The method of claim 9, wherein said first value is equal to said second value.

11. The method of claim 7, wherein the computer system further includes cache memory and main memory coupled to the processor and wherein said step of counting events comprises the step of:

counting cache read miss operations and main memory write operations.

12. The method of claim 7, wherein the computer system further includes cache memory, paged memory and input/output devices, and wherein said step of counting events comprises the step of:

counting events selected from the group consisting of cache read miss and memory write operations, memory page miss operations, and input/output write operations.

13. An apparatus for use with a computer system for reducing power consumption of the computer system, comprising:

a processor having a clocking input;

means for producing a clocking signal having a frequency;

cache memory coupled to said processor;

main memory coupled to said processor, and having a main memory cycle is performed during write operations and cache read miss operations;

a counter coupled to said processor and said main memory for counting a number of main memory cycles;

means coupled to said counter and said processor for periodically reading said counter to determine the counted number of main memory cycles;

means coupled to said periodic reading means and said clocking signal producing means for adjusting the frequency of the clocking signal based on the counted number of main memory cycles from said periodic reading means; and

means coupled to said frequency adjusting means for outputting the frequency adjusted clocking signal to said processor clocking input.

14. The apparatus of claim 13, further comprising:

means coupled to said adjusting means for determining the current frequency of said clocking signal; and

wherein said adjusting means further adjusts the frequency of said clocking signal based on said current frequency of said clocking signal.

15. The apparatus of claim 13, wherein said adjusting means includes:

means for determining if said clocking signal is operating at a higher or lower frequency;

means coupled to said periodic reading means for determining if said counted number of events is greater than a first value if said clocking signal is operating at said lower frequency;

means coupled to said greater than determining means and said clocking signal producing means for increasing the frequency of said clocking signal if said counted number of events is greater than said first value and said clocking signal is operating at said lower frequency;

means coupled to said periodic reading means for determining if said counted number of events is less than a second value if said clocking signal is operating at said higher frequency; and

means coupled to said less than determining means and said clocking signal producing means for decreasing the frequency of said clocking signal if said counted number of events is less than said second value and said clocking signal is operating at said higher frequency.

16. The apparatus of claim 15, wherein said first value is equal to said second value.

17. The apparatus of claim 13, wherein said event comprises cache read miss operations and main memory write operations.

18. The apparatus of claim 13, further comprising:

input/output devices coupled to said processor;

wherein said main memory is organized as paged memory;

wherein said counter further counts the number of input/output write cycles and page miss operations; and

wherein said adjusting means adjusts the frequency of said clocking signal additionally based on main memory page miss operations and input/output write operations.

19. A method for reducing power consumption of a computer system including a processor, a producer of a clocking signal that is provided to the processor, the clocking signal having a frequency, cache memory coupled to the processor, and main memory coupled to the processor, wherein a main memory cycle is performed during write operations and cache read miss operations, the method comprising:

counting a number of main memory cycles in the computer system;

periodically determining counted number of main memory cycles;

adjusting the frequency of the clocking signal from the clocking signal producer based on the counted number of main memory cycles; and

outputting the frequency adjusted clocking signal to the processor.

20. The method of claim 19, further comprising:

determining current operating frequency of the clocking signal; and

wherein said step of adjusting further comprises adjusting the frequency of the clocking signal based on said current operating frequency of the clocking signal.

21. The method of claim 19, wherein said step of adjusting includes:

determining if the clocking signal is operating at a higher or lower frequency;

determining if said counted number of main memory cycles is greater than a first value if the clocking signal is operating at said lower frequency;

increasing the frequency of the clocking signal if said counted number of main memory cycles is greater than said first value and the clocking signal is operating at said lower frequency;

determining if said counted number of main memory cycles is less than a second value if the clocking signal is operating at said higher frequency; and

decreasing the frequency of said clocking signal if said counted number of main memory cycles is less than said second value and the clocking signal is operating at said higher frequency.

22. The method of claim 21, wherein said first value is equal to said second value.