Disk drive adjusting rotational position optimization (RPO) algorithm to compensate for repeatable runout (RRO)

1. A disk drive comprising:

a first disk surface comprising a plurality of tracks, wherein each track comprises a number of data sectors and a number of servo sectors;

a second disk surface comprising a plurality of tracks, wherein each track comprises a number of data sectors and a number of servo sectors;

a head actuated over each disk surface; and

control circuitry operable to:

generate a first repeatable runout (RRO) sinusoid representing an RRO of the first disk surface;

generate a second RRO sinusoid representing an RRO of the second disk surface;

receive a plurality of access commands from a host;

store the access commands in a command queue; and

select one of the access commands to execute in response to the first and second RRO sinusoids.

2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

compute a difference between the first and second RRO sinusoids; and

select one of the access commands to execute in response to the difference.

3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

generate the first RRO sinusoid according to:

a1 cos(2πk/N)+b1 sin(2πk/N);

generate the second RRO sinusoid according to:

a2 cos(2πk/N)+b2 sin(2πk/N);

where:

a1, b1, a2, b2 are coefficients;

k represents a servo sector index; and

N is the number of servo sectors.

4. The disk drive as recited in claim 3 , wherein the control circuitry is further operable to compute a difference between the first and second RRO sinusoids according to:

[a1 cos(2πi/N)+b1 sin(2πi/N)]−[a2 cos(2πi/N)+b2 sin(2πi/N)]

where i represents a starting servo sector of a seek operation.

5. The disk drive as recited in claim 3 , wherein the control circuitry is further operable to compute a difference between the first and second RRO sinusoids according to:

[a1 cos(2πj/N)+b1 sin(2πj/N)]−[a2 cos(2πj/N)+b2 sin(2πj/N)]

where j represents an ending servo sector of a seek operation.

6. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to compute a difference between the first and second RRO sinusoids according to:

[a1 cos(2π(i−Δ 1 )/N)+b1 sin(2π(i−Δ 1 )/N)]−[a2 cos(2π(i−Δ 2 )/N)+b2 sin(2π(i−Δ 2 )/N)]

where Δ 1 and Δ 2 represent a skew between the servo sectors of the first and second disk surfaces.

7. The disk drive as recited in claim 5 , wherein the control circuitry is further operable to compute a difference between the first and second RRO sinusoids according to:

[a1 cos(2π(j−Δ 1 )/N)+b1 sin(2π(j−Δ 1 )/N)]−[a2 cos(2π(j−Δ 2 )/N)+b2 sin(2π(j−Δ 2 )/N)]

where Δ 1 and Δ 2 represent a skew between the servo sectors of the first and second disk surfaces.

8. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to select one of the access commands to execute in response to the first and second RRO sinusoids and a skew between the servo sectors of the first and second disk surfaces.

9. A method of operating a disk drive, the disk drive comprising a first disk surface comprising a plurality of tracks, wherein each track comprises a number of data sectors and a number of servo sectors, a second disk surface comprising a plurality of tracks, wherein each track comprises a number of data sectors and a number of servo sectors, and a head actuated over each disk surface, the method comprising:

generating a first repeatable runout (RRO) sinusoid representing an RRO of the first disk surface;

generating a second RRO sinusoid representing an RRO of the second disk surface;

receiving a plurality of access commands from a host;

storing the access commands in a command queue; and

selecting one of the access commands to execute in response to the first and second RRO sinusoids.

10. The method as recited in claim 9 , further comprising:

computing a difference between the first and second RRO sinusoids; and

selecting one of the access commands to execute in response to the difference.

11. The method as recited in claim 9 , further comprising:

generating the first RRO sinusoid according to:

a1 cos(2πk/N)+b1 sin(2πk/N);

generating the second RRO sinusoid according to:

a2 cos(2πk/N)+b2 sin(2πk/N);

where:

a1, b1, a2, b2 are coefficients;

k represents a servo sector index; and

N is the number of servo sectors.

12. The method as recited in claim 11 , further comprising computing a difference between the first and second RRO sinusoids according to:

[a1 cos(2πi/N)+b1 sin(2πi/N)]−[a2 cos(2πi/N)+b2 sin(2πi/N)]

where i represents a starting servo sector of a seek operation.

13. The method as recited in claim 11 , further comprising computing a difference between the first and second RRO sinusoids according to:

[a1 cos(2πj/N)+b1 sin(2πj/N)]−[a2 cos(2πj/N)+b2 sin(2πj/N)]

where j represents an ending servo sector of a seek operation.

14. The method as recited in claim 12 , further comprising computing a difference between the first and second RRO sinusoids according to:

[a1 cos(2π(i−Δ 1 )/N)+b1 sin(2π(i−Δ 1 )/N)]−[a2 cos(2π(i−Δ 2 )/N)+b2 sin(2π(i−Δ 2 )/N)]

where Δ 1 and Δ 2 represent a skew between the servo sectors of the first and second disk surfaces.

15. The method as recited in claim 13 , further comprising computing a difference between the first and second RRO sinusoids according to:

[a1 cos(2π(j−Δ 1 )/N)+b1 sin(2π(j−Δ 1 )/N)]−[a2 cos(2π(j−Δ 2 )/N)+b2 sin(2π(j−Δ 2 )/N)]

where Δ 1 and Δ 2 represent a skew between the servo sectors of the first and second disk surfaces.

16. The method as recited in claim 9 , further comprising selecting one of the access commands to execute in response to the first and second RRO sinusoids and a skew between the servo sectors of the first and second disk surfaces.