Conserving power by reducing voltage supplied to an instructions-processing portion of a processor

Abstract

One embodiment of the present invention provides a system that facilitates reducing static power consumption of a processor. During operation, the system receives a signal indicating that instruction execution within the processor is to be temporarily halted. In response to this signal, the system halts an instruction-processing portion of the processor, and reduces the voltage supplied to the instruction-processing portion of the processor. Full voltage is maintained to a remaining portion of the processor, so that the remaining portion of the processor can continue to operate while the instruction-processing portion of the processor is in reduced power mode.

What is claimed is: 
     
         1 . A processor, comprising:
 a first power area that comprises an instruction-processing portion of the processor and operates responsive to a first voltage and a first clock signal that are supplied to the first power area; and   a second power area that comprises a second portion of the processor and operates responsive to a second voltage that is supplied to the second power area;   wherein the first power area of the processor operates in one of a normal operation mode when the first voltage is at a first level, a first power-saving mode when the first voltage is at a second level, and a second power-saving mode when the first voltage is at a third level; and   wherein the first power area of the processor is configured to transition from the normal operation mode to the first or second power saving mode based, at least in part, on a comparison of a cost of entering and exiting from the first or second power saving mode with a cost of remaining in the normal operation mode.   
     
     
         2 . The processor of  claim 1 , wherein in the normal operation mode:
 the first clock signal is active;   the first voltage is sufficient for the instruction-processing portion of the processor to process instructions; and   the second voltage is sufficient for the second portion of the processor to operate.   
     
     
         3 . The processor of  claim 2 , wherein in the first power-saving mode:
 the first clock signal is inactive;   the first voltage is sufficient to maintain a state of the instruction-processing portion of the processor; and   the second voltage is sufficient for the second portion of the processor to operate.   
     
     
         4 . The processor of  claim 3 , wherein the processor transitions from the first power-saving mode to the normal operation mode responsive to an interrupt signal. 
     
     
         5 . The processor of  claim 3 , wherein in the second power-saving mode:
 the first clock signal is inactive;   the first voltage is reduced; and   the second voltage is sufficient for the second portion of the processor to operate.   
     
     
         6 . The processor of  claim 5 , wherein the processor transitions from the second power-saving mode to the normal operation mode responsive to a signal that is at least one of an interrupt signal and a signal indicating that processing is to resume. 
     
     
         7 . The processor of  claim 5 , wherein the first voltage is reduced to zero. 
     
     
         8 . The processor of  claim 5 , wherein the state of the instruction-processing portion of the processor is saved to a memory before the first voltage is reduced to a level that is not sufficient to maintain the state. 
     
     
         9 . The processor of  claim 8 , wherein the memory is external to the processor. 
     
     
         10 . The processor of  claim 1 , wherein the second power area comprises an interrupt processor. 
     
     
         11 . The processor of  claim 1 , wherein the second power area comprises snoop circuitry. 
     
     
         12 . The processor of  claim 1 , wherein the second power area comprises a cache memory. 
     
     
         13 . The processor of  claim 1 , wherein the processor transitions to the first power-saving mode responsive to a determination that the instruction-processing portion is not needed soon. 
     
     
         14 . The processor of  claim 1 , wherein the processor transitions to the second power-saving mode responsive to a determination that the instruction-processing portion is not needed soon and the instruction-processing portion has been taking long naps recently. 
     
     
         15 . A method, comprising:
 in a processor that comprises a first power area that comprises an instruction-processing portion of the processor and operates responsive to a first voltage and a first clock signal that are supplied to the first power area, and a second power area that comprises a second portion of the processor and operates responsive to a second voltage that is supplied to the second power area, operating the first power area of the processor in one of a normal operation mode when the first voltage is at a first level, a first power-saving mode when the first voltage is at a second level, and a second power-saving mode when the first voltage is at a third level.   
     
     
         16 . The method of  claim 15 , wherein operating the processor in the normal operation mode comprises:
 providing, for the first clock signal, an active clock signal;   providing, for the first voltage, a voltage sufficient for the instruction-processing portion of the processor to process instructions; and   providing, for the second voltage, a voltage sufficient for the second portion of the processor to operate.   
     
     
         17 . The method of  claim 16 , wherein operating the processor in the first power-saving mode comprises:
 providing, for the first clock signal, an inactive clock signal;   providing, for the first voltage, a voltage sufficient to maintain a state of the instruction-processing portion of the processor; and   providing, for the second voltage, a voltage sufficient for the second portion of the processor to operate.   
     
     
         18 . The method of  claim 17 , further comprising:
 transitioning the processor from the first power-saving mode to the normal operation mode responsive to an interrupt signal.   
     
     
         19 . The method of  claim 17 , wherein operating the processor in the second power-saving mode comprises:
 providing, for the first clock signal, an inactive clock signal;   providing, for the first voltage, a reduced voltage; and   providing, for the second voltage, a voltage sufficient for the second portion of the processor to operate.   
     
     
         20 . The method of  claim 19 , further comprising:
 transitioning the processor from the second power-saving mode to the normal operation mode responsive to a signal that is not an interrupt signal.   
     
     
         21 . The method of  claim 19 , wherein providing, in the second power saving mode, for the first voltage, a reduced voltage comprises providing zero volts. 
     
     
         22 . The method of  claim 19 , further comprising:
 saving the state of the instruction-processing portion of the processor to a memory before the first voltage is reduced to a level that is not sufficient to maintain the state.   
     
     
         23 . The method of  claim 22 , wherein the memory is external to the processor. 
     
     
         24 . The method of  claim 15 , wherein the second power area comprises an interrupt processor. 
     
     
         25 . The method of  claim 15 , wherein the second power area comprises snoop circuitry. 
     
     
         26 . The method of  claim 15 , wherein the second power area comprises a cache memory. 
     
     
         27 . The method of  claim 15 , further comprising:
 transitioning the processor to the first power-saving mode responsive to a determination that the instruction-processing portion is not needed soon.   
     
     
         28 . The method of  claim 15 , further comprising:
 transitioning the processor to the second power-saving mode responsive to a determination that the instruction-processing portion is not needed soon and the instruction-processing portion has been taking long naps recently.