Idle-element prediction circuitry and anti-thrashing logic

• US 20060259791A1
• Filed: 05/10/2005
• Published: 11/16/2006
• Est. Priority Date: 05/10/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Dockser, Kenneth Alan
• Granted Patent: US 7,386,747 B2
• Time in Patent Office: Days
• US Class Current: 713/300
• CPC Class Codes: G06F 1/3228 Monitoring task completion, e.g. by use of idle timers, stop commands or wait commands
• CPC Class Codes: G06F 1/3287 by switching off individual functional units in the computer system
• CPC Class Codes: G06F 9/3869 Implementation aspects, e.g. pipeline latches; pipeline synchronisation and clocking
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management
• CPC Class Codes: Y02D 30/50 in wire-line communication networks, e.g. low power modes or reduced link rate

Abstract

Control logic monitors use of a particular functional element (e.g., a divider, or multiplier or the like) in a programmable processor, and the control logic powers the unit down when it has not been used for a specified time period. A counter (local or central) and time threshold determine when the period has elapsed without use of the element. The control logic also monitors how soon the functional unit is woken up again, to determine if power control is causing thrashing. Upon the determination of such thrashing, the unit automatically adjusts its threshold period, to minimize thrashing. In an example of the logic, when it determines that it is being too conservative, it lowers the threshold. Mode bits may allow the programmer to override the power-down logic to either keep the logic always powered-up, or always powered-down.

Claims

1. A method of reducing power consumption of a programmable processor comprising:

monitoring time since a last call for an operation of one of a plurality of functional units of the programmable processor;

monitoring time since a last prior shut down of the one functional unit;

when the time since the last call exceeds a current threshold, shutting down the one functional unit, so as to reduce power consumed by the one functional unit;

reactivating the one functional unit in response to a later call for operation of the one functional unit; and

if at the time of reactivating the one functional unit, the time since the shutting down is less than a set value, increasing the current threshold to a new higher threshold.

2. The method of claim 1, wherein the set value equals the current value of the threshold.

3. The method of claim 1, wherein the new higher threshold is twice the current threshold.

4. The method of claim 1, further comprising adjusting the current threshold to optimize power reduction based on the time since the last call for operation of the one functional unit, upon shutting down the one functional.

5. The method of claim 4, wherein the adjusting of the current threshold to optimize power reduction comprises calculating an adjusted threshold value by performing steps comprising:

subtracting the time since the last call from the current threshold to obtain a difference;

shifting the difference by one or more bit positions; and

subtracting the shifted difference from the current threshold to obtain the adjusted threshold value.

6. The method of claim 5, wherein the calculating of the adjusted threshold value further comprises saturating the difference to no more than the current threshold and limiting the adjusted threshold value to no less than a set minimum threshold value.

7. The method of claim 1, wherein the functional unit comprises a logic element for execution of an arithmetic function.

8. The method of claim 7, wherein the arithmetic function comprises a multiply or a divide function.

9. A method of reducing power consumption of a programmable processor comprising:

monitoring calls for an operation of one of a plurality of functional units of the programmable processor;

shutting down the one functional unit in response to each detection of the time following a last preceding one of the calls reaching a current value of a threshold before a subsequent one of the calls;

activating the one functional unit in response to a call for operation of the one functional unit following each shutting down of the one functional unit;

monitoring time between each shutting down of the one functional unit and each subsequent activation of the one functional unit; and

increasing the threshold to a new current value, in response to any occurrence of time between a shutting down of the one functional unit and a subsequent activation of the one functional unit being less than a set period.

10. The method of claim 9, wherein the set period equals the current value of the threshold.

11. A power control for a programmable processor comprising a plurality of functional units, the power control comprising:

circuitry coupled to one of the functional units, for selectively activating and shutting down the one functional unit;

means for monitoring time since a last prior call for operation of the one functional unit and time since a last prior shutting down of the one functional unit;

means for controlling the circuitry, to shut down the one functional unit upon each occurrence of time since last call for operation of the one functional unit exceeding a current value of a threshold and for increasing the threshold over its current value if a call for the one functional unit occurs in a time since last prior shutting down of less than a set value.

12. The power control as in claim 12, wherein the set value equals the current value of the threshold.

14. The power control as in claim 12, further comprising means for adjusting the threshold as a function of time since last call for the one functional unit upon each shut down of the one functional unit.

13. The power control as in claim 13, wherein the increasing of the threshold comprises setting a new threshold value equal to double the current value of the threshold.

15. A programmable processor, comprising:

a plurality of functional units for processing data in accord with instructions;

circuitry coupled to one of the functional units, for selectively activating and shutting down the one functional unit;

a power controller, for monitoring calls for operation of the one functional unit during the processing of instructions and controlling the circuitry to shut down the one functional unit upon each passage of a time interval since a last prior one of the calls equal to an adjustable threshold and to reactivate the one functional unit in response to each new call for operation of the one functional unit following a shut down; and

means for adjusting the threshold.

16. The programmable processor as in claim 15, wherein the means control an increase of the threshold as a function of time between a shut down of the one functional unit and a subsequent call for the operation of the one functional unit.

17. The programmable processor as in claim 15, wherein the means control a decrease of the threshold as a function of time since last call for the operation of the one functional unit in response to a subsequent call for operation of the one functional unit.

18. The programmable processor as in claim 15, wherein:

the means increase the threshold if time between a shut down of the one functional unit and a subsequent call for the operation of the one functional unit is less than a set value;

otherwise

the means for adjusting adjust the threshold as a function of time since last call for the operation of the one functional unit.

19. The processor of claim 15, wherein the functional units form a plurality of processing stages of a pipeline, the stages include an execution stage, and the one functional unit comprises an element of the execution stage.

20. The processor of claim 19, wherein the element of the execution stage comprises a divider or a multiplier.