Method and apparatus for setting VDD on a per chip basis

1. A test system comprising:

an integrated circuit coupled to a voltage source and a current monitor; and

a controller configured to:

cause the voltage source to supply a voltage to the integrated circuit;

receive an indication from the current monitor indicative of a power dissipation of the integrated circuit;

cause the voltage source to progressively reduce a voltage supplied to the integrated circuit;

identify a particular voltage which corresponds to an indication that a power dissipation of the integrated circuit is less than a predetermined threshold; and

store in the integrated circuit a value corresponding to a voltage supplied to the integrated circuit when the power dissipation of the integrated circuit is less than the predetermined threshold.

2. The system of claim 1 , wherein the integrated circuit comprises:

a plurality of access pins; and

a non-volatile storage register;

wherein the value is stored in at least a portion of the non-volatile storage register; and

wherein the non-volatile storage register is accessible via a subset of the access pins; and

wherein the subset of the access pins provides at least one function in addition to accessing the non-volatile storage register.

3. The system of claim 2 , wherein the plurality of access pins comprise a JTAG interface.

4. The system of claim 2 , wherein the at least a portion of the non-volatile storage register comprises one or more electrical fuses.

5. The system of claim 1 , wherein the controller is further configured to:

cause the integrated circuit to operate at a first clock speed;

test operation of the integrated circuit at the first clock speed; and

test operation of the integrated circuit at a second clock speed lower than the first clock speed, if the integrated circuit passes the operating test at the first clock speed and a power dissipation of the integrated circuit is greater than the predetermined threshold.

6. The system of claim 1 , wherein the controller is further configured to:

cause the integrated circuit to operate at a first clock speed;

test operation of the integrated circuit at the first clock speed; and

if the integrated circuit passes the operating test at the first clock speed and the power dissipation of the integrated circuit is less than the predetermined threshold:

cause the voltage source to increase the voltage;

cause the integrated circuit to operate at a second clock speed which is higher than the first clock speed; and

test operation of the integrated circuit at the second clock speed.

7. The system of claim 1 , wherein the value which is stored in the integrated circuit corresponds to the particular voltage.

8. The system of claim 1 , wherein the integrated circuit is marked with a nominal operating voltage and a value which indicates a difference between the nominal operating voltage and a voltage supplied to the integrated circuit when a power dissipation of the integrated circuit is less than the predetermined threshold.

9. An apparatus comprising:

an integrated circuit including:

a non-volatile storage register; and

a plurality of access pins, wherein at least a subset of the access pins provides at least one function in addition to providing access to the non-volatile storage register;

wherein the integrated circuit is:

operable at a level of power dissipation above a predetermined threshold, responsive to a first voltage; and

operable at a level of power dissipation below a predetermined threshold voltage, responsive to a second voltage;

wherein the non-volatile storage register is:

configured to store a value corresponding to the second voltage; and

accessible via a subset of the access pins while the integrated circuit is operating at the first voltage.

10. The apparatus of claim 9 , wherein the integrated circuit is one of a processor, a memory, a programmable logic device, an application specific integrated circuit, and a digital signal processor.

11. The apparatus of claim 9 , wherein the integrated circuit is marked with a nominal operating voltage and a value which indicates a difference between the nominal operating voltage and the second voltage.

12. The apparatus of claim 9 , wherein the integrated circuit is coupled to a voltage source and a controller,

wherein the controller is configured to:

cause the voltage source to supply a voltage to the integrated circuit;

retrieve a value from the integrated circuit; and

cause the voltage source to change the voltage responsive to the value retrieved from the integrated circuit.

13. The apparatus of claim 9 , wherein the plurality of access pins comprises a JTAG interface.

14. The apparatus of claim 9 , wherein the at least a portion of the non-volatile storage register comprises one or more electrical fuses.

15. A method of testing comprising:

supplying a first voltage to an integrated circuit;

supplying a clock to the integrated circuit at a first clock speed; and

if the integrated circuit fails an operating test at the first clock speed and the power dissipation of the integrated circuit is less than a predetermined threshold:

increasing the voltage supplied to the integrated circuit to a second voltage; and

storing in the integrated circuit a value corresponding to the second voltage if the integrated circuit passes an operating test at the second voltage and the power dissipated by the integrated circuit is less than the predetermined threshold.

16. The method of claim 15 , wherein if the integrated circuit passes an operating test at the first clock speed and a power dissipation of the integrated circuit is greater than the predetermined threshold, the method further comprises:

reducing the first voltage until a power dissipated by the integrated circuit is less than the predetermined threshold; and

storing in the integrated circuit a value corresponding to a voltage supplied to the integrated circuit when the power dissipated by the integrated circuit is less than the predetermined threshold.

17. The method of claim 16 , wherein the integrated circuit comprises a plurality of access pins and a non-volatile storage register, and wherein the method further comprises accessing the non-volatile storage register via a subset of the access pins, wherein the subset of the access pins provides at least one function in addition to providing access to the non-volatile storage register.

18. The method of claim 17 , wherein the plurality of access pins comprises a JTAG interface.

19. The method of claim 17 , wherein the at least a portion of the non-volatile storage register comprises one or more electrical fuses.

20. The method of claim 16 , wherein if the integrated circuit passes an operating test at the first clock speed and a power dissipation of the integrated circuit is greater than the predetermined threshold, the method further comprises:

supplying a clock to the integrated circuit at a second clock speed which is lower than the first clock speed; and

testing operation of the integrated circuit at the second clock speed.