Disk drive comprising a servo accelerator employing a dual state variable memory

1. A disk drive comprising:

a disk;

a head;

an actuator for actuating the head over the disk; and

control circuitry operable to generate an actuator control signal by:

assigning a memory address to a first state variable memory (SVM 1 );

using the memory address to read a first state k variable from the SVM 1 ;

storing the first state k variable in a second state variable memory (SVM 2 ) while processing the first state k variable to generate a first state k+1 variable;

storing the first state k+1 variable in the SVM 2 ;

assigning the memory address to the SVM 2 so that the first state k+1 variable becomes a second state k variable and the first state k variable becomes a first state k−1 variable;

using the memory address to read the second state k variable and the first state k−1 variable from the SVM 2 ;

storing the second state k variable in the SVM 1 while processing the second state k variable and the first state k−1 variable to generate a second state k+1 variable;

storing the second state k+1 variable in the SVM 1 ; and

assigning the memory address to the SVM 1 so that the second state k+1 variable becomes a third state k variable.

2. The disk drive as recited in claim 1 , wherein the control circuitry comprises a demultiplexer for assigning the memory address to one of the SVM 1 and the SVM 2 .

3. The disk drive as recited in claim 1 , wherein the control circuitry further comprises a multiply/accumulate circuit for processing the state k variables.

4. The disk drive as recited in claim 3 , wherein the multiply/accumulate circuit multiplies the first state k variable by a coefficient.

5. The disk drive as recited in claim 4 , wherein the control circuitry comprises a notch filter wherein the first state k variable is an input to the notch filter and the first state k+1 variable is an output of the notch filter.

6. The disk drive as recited in claim 5 , wherein the second state k variable is an input to the notch filter and the second state k+1 variable is an output of the notch filter.

7. The disk drive as recited in claim 1 , wherein the actuator comprises a voice coil motor.

8. The disk drive as recited in claim 7 , wherein the actuator comprises a piezoelectric actuator.

9. A method of generating an actuator control signal in a disk drive, the disk drive comprising a disk, a head, and an actuator for actuating the head over the disk, the method comprising:

assigning a memory address to a first state variable memory (SVM 1 );

using the memory address to read a first state k variable from the SVM 1 ;

storing the first state k variable in a second state variable memory (SVM 2 ) while processing the first state k variable to generate a first state k+1 variable;

storing the first state k+1 variable in the SVM 2 ;

assigning the memory address to the SVM 2 so that the first state k+1 variable becomes a second state k variable and the first state k variable becomes a first state k−1 variable;

using the memory address to read the second state k variable and the first state k−1 variable from the SVM 2 ;

storing the second state k variable in the SVM 1 while processing the second state k variable and the first state k−1 variable to generate a second state k+1 variable;

storing the second state k+1 variable in the SVM 1 ; and

assigning the memory address to the SVM 1 so that the second state k+1 variable becomes a third state k variable.

10. The method as recited in claim 9 , further comprising assigning the memory address to one of the SVM 1 and the SVM 2 using a demultiplexer.

11. The method as recited in claim 9 , further comprising processing the state k variables using a multiply/accumulate circuit.

12. The method as recited in claim 11 , further comprising multiplying the first state k variable by a coefficient using the multiply/accumulate circuit.

13. The method as recited in claim 12 , further comprising inputting the first state k variable into a notch filter and outputting the first state k+1 variable from the notch filter.

14. The method as recited in claim 13 , further comprising inputting the second state k variable into the notch filter and outputting the second state k+1 variable from the notch filter.

15. The method as recited in claim 9 , wherein the actuator comprises a voice coil motor.

16. The method as recited in claim 15 , wherein the actuator comprises a piezoelectric actuator.