Detection of fuse re-growth in a microprocessor

A method for operating a microprocessor, the method comprising:

• providing control values from a first plurality of fuses to circuits of the microprocessor to control operation of the microprocessor, wherein a predetermined number of the first plurality of fuses are selectively blown;
• reading the predetermined number and a Boolean complement of the predetermined number from a second plurality of fuses, wherein the second plurality of fuses is blown with the predetermined number of the first plurality of fuses that are blown and the Boolean complement of the predetermined number;
• Boolean complementing the predetermined number read from the second plurality of fuses to generate a result;
• comparing the result with the Boolean complement of the predetermined number read from the second plurality of fuses;
• and
• preventing the microprocessor from fetching and executing user program instructions if the result does not equal the Boolean complement of the predetermined number read from the second plurality of fuses.

A method for manufacturing a microprocessor having a capability to detect an incorrect control value provided by a first plurality of fuses of the microprocessor to circuits of the microprocessor during operation of the microprocessor to control operation thereof, the control value being incorrect because a blown one or more of the first plurality of fuses is providing its non-blown value rather than its blown value, the method comprising:

• determining the control value;
• counting a number of the first plurality of fuses to be blown to create the control value in the first plurality of fuses;
• blowing the control value into the first plurality of fuses;
• blowing into a second plurality of fuses of the microprocessor the number of the first plurality of fuses blown to create the control value;
• and
• blowing into the second plurality of fuses a Boolean complement of the number.

A computer program product encoded in at least one computer readable medium for use with a computing device, the computer program product comprising:

• computer readable program code embodied in said medium, for specifying a microprocessor, the computer readable program code comprising:
• first program code for specifying a first plurality of fuses, a predetermined number of which are selectively blown, wherein control values are provided from the first plurality of fuses to circuits of the microprocessor to control operation of the microprocessor;
• and
• second program code for specifying a second plurality of fuses, blown with the predetermined number of the first plurality of fuses that are blown and a Boolean complement of the predetermined number;
• wherein, in response to being reset, the microprocessor is configured to:
• read the predetermined number and the Boolean complement of the predetermined number from the second plurality of fuses;
• Boolean complement the predetermined number read from the second plurality of fuses to generate a result;
• compare the result with the Boolean complement of the predetermined number read from the second plurality of fuses;
• and
• prevent itself from fetching and executing user program instructions if the result does not equal the Boolean complement of the predetermined number read from the second plurality of fuses.