Method and program for setting microprocessor power supply voltage

1. A method for setting a power supply voltage to be supplied to a microprocessor, the method comprising:

determining a state of the microprocessor; and

setting the power supply voltage according to the state determined by the determining,

wherein the determining and the setting are performed in a state where the microprocessor is mounted on an electronic device on which the microprocessor is finally installed, the determining includes measuring a cumulative operating time of the microprocessor, and the setting sets the power supply voltage according to the cumulative operating time measured by the measuring.

2. A method according to claim 1 , wherein the determining is performed repeatedly in predetermined timing, and

wherein whenever the determining is performed, the power supply voltage is reset by the setting.

3. A method according to claim 1 , wherein the determining executes a predetermined determination program using the microprocessor, and

wherein the setting is such that the power supply voltage is set based on a result of execution of the determination program in the determining.

4. A method according to claim 3 , wherein the determining is such that the power supply voltage supplied to the microprocessor is lowered successively as a predetermined processing is executed by the microprocessor, and

wherein the setting detects a lower limit voltage for an operation of the microprocessor and sets a voltage near the detected lower limit voltage as the power supply voltage, such that the voltage near the detected lower limit voltage is a latest power supply voltage at which the microprocessor could execute the pre determined processing.

5. A method according to claim 3 , further comprising updating the determination program after shipment of an electronic device equipped with the microprocessor.

6. A method according to claim 3 , wherein the determination program includes a processing code that sets a maximum power supply voltage necessary for the microprocessor.

7. A method according to claim 1 , wherein the determining measures a characteristic indicative of a lower limit of operating voltage of the microprocessor, and

wherein the setting sets the power supply voltage according to the measured characteristic indicative thereof.

8. A method according to claim 7 , wherein the characteristic indicative thereof is an oscillation frequency of a ring oscillator provided within the microprocessor, and

wherein the setting sets the power supply voltage based on the measured oscillation frequency.

9. An arithmetic processor, comprising:

a microprocessor;

a determining unit which determines a state of the microprocessor;

a setting unit which sets a power supply voltage to be supplied to the microprocessor according to the state of the microprocessor determined by the determining unit; and

a power supply circuit which supplies the power supply voltage set by the setting unit, to the microprocessor,

wherein the determining unit includes a measuring unit which measures a cumulative operating time of the microprocessor as the state of the microprocessor, and the settting unit sets the power supply voltage according to the cumulative operating time measured by the measuring unit.

10. An arithmetic processor according to claim 9 , wherein the determining unit determines the state of the microprocessor repeatedly in predetermined timing, and

wherein whenever the determination is performed by the determining unit, the setting unit resets the power supply voltage.

11. An arithmetic processor according to claim 9 , wherein the determining unit executes a predetermined determination program using the microprocessor, and

wherein the setting unit sets the power supply voltage based on a result of execution of the determination program.

12. An arithmetic processor according to claim 11 , wherein the setting unit and the power supply circuit successively lower the power supply voltage supplied to the microprocessor as a predetermined processing is executed by the microprocessor, and

wherein the setting unit detects a lower limit voltage for an operation of the microprocessor and sets a voltage near the detected lower limit voltage as the power supply voltage such that the voltage near the detected lower limit voltage is a voltage with a given margin added to the detected lower limit voltage.

13. An arithmetic processor according to claim 11 , further comprising an updating unit which updates the determination program after shipment of an electronic device equipped with the microprocessor.

14. An arithmetic processor according to claim 11 , wherein the determining unit causes the microprocessor to execute the determination program where the determination program includes a processing code that sets a maximum power supply voltage necessary for the microprocessor.

15. An arithmetic processor according to claim 9 , wherein the determining unit measures a characteristic indicative of a lower limit of operating voltage of the microprocessor, and

wherein the setting unit sets the power supply voltage according to the measured characteristic indicative thereof.

16. An arithmetic processor according to claim 15 , wherein the microprocessor includes a ring oscillator, and

wherein the determining unit includes a frequency measurement unit which measures an oscillation frequency of the ring oscillator as the characteristic indicative of a lower limit of operating voltage, and

wherein the setting unit sets the power supply voltage based on the oscillation frequency measured by the frequency measurement unit.