System for controlling rotation of a disk drive

1. A disk drive system comprising:

a rotatable storage medium adapted to store data;

a spindle motor disposed to rotate the rotatable storage medium;

a control system operating to inductively sense spindown of the spindle motor by

executing an inductive sensing cycle through all states, S 1 through S total , of the spindle motor to determine a minimum current rise time value, T min1 , occurring at a spindle motor state, S min1 , and

executing a further inductive sensing cycle through all states, S 1 through S total , of the spindle motor to determine a further minimum current rise time value, T min2 , occurring at a spindle motor state S min2 ,

where the control system executes a braking operation of the spindle motor and re-executes the inductive sensing cycle and further inductive sensing cycle if S min1 is different from S min2 .

2. The system of claim 1 , where the rotatable storage medium comprises a hard disk.

3. The system of claim 1 , where the spindle motor control system compares a difference value to a threshold value to determine whether the spindle motor has substantially ceased rotating before executing the braking operation, where the difference value corresponds to T 2min −T 1min .

4. The system of claim 1 , where the spindle motor control system comprises:

a motor drive system disposed to provide PWM drive power to the spindle motor;

a current sense circuit disposed to monitor drive current provided to the spindle motor by the motor drive system;

a processing circuit disposed to control operation of the motor drive system and to receive one or more signals from the current sense circuit indicative of a value of the drive current;

firmware executable by the processing circuit to direct the motor drive system to brake rotation of the spindle motor in response to inductive sensing of the rotation of the spindle motor.

5. A disk drive system comprising:

rotatable storage means for storing data;

spindle motor means for rotating the rotatable storage means;

spindle motor control means for controlling the spindle motor means, where the spindle motor control means inductively senses spindown of the spindle motor means by

executing an inductive sensing cycle through all states, S 1 through S total , of the spindle motor means to determine a minimum current rise time value, T min1 , occurring at a state, S min1 , of the spindle motor means, and

executing a further inductive sensing cycle through all states, S 1 through S total , of the spindle motor means to determine a further minimum current rise time value, T min2 , occurring at a state S min2 of the spindle motor means,

where the spindle motor control means executes a braking operation of the spindle motor means and re-executes the inductive sensing cycle and further inductive sensing cycle if S min1 is different from S min2 .

6. The system of claim 5 , where the rotatable storage means comprises a hard disk.

7. The system of claim 5 , where the spindle motor control means compares a difference value to a threshold value to determine whether the spindle motor means has substantially ceased rotating before executing the braking operation, where the difference value corresponds to T 2min −T 1min .

8. The system of claim 5 , where the spindle motor control means comprises:

motor drive means for providing PWM drive power to the spindle motor means;

current sense means for monitoring drive current provided to the spindle motor means by the motor drive means;

processing means for controlling operation of the motor drive means and to receive one or more signals from the current sense means indicative of a value of the drive current;

firmware means for directing the motor drive system to brake rotation of the spindle motor means in response to inductive sensing of the rotation of the spindle motor means, where the firmware means is executable by the processing means.

9. A process for operating a disk drive system comprising:

storing data on a rotatable storage medium;

rotating the rotatable storage medium with a spindle motor;

inductively sensing spindown of the spindle motor by

executing an inductive sensing cycle through all states, S 1 through S total , of the spindle motor to determine a minimum current rise time value, T min1 , occurring at a state, S min1 , of the spindle motor, and

executing a further inductive sensing cycle through all states, S 1 through S total , of the spindle motor to determine a further minimum current rise time value, T min2 , occurring at a state S min2 of the spindle motor,

executing a braking operation of the spindle motor and re-executing the inductive sensing cycle and further inductive sensing cycle if S min1 is different from S min2 .

10. The process of claim 9 , where storing data comprises storing data on a hard disk.

11. The process of claim 9 , further comprising comparing a difference value to a threshold value to determine whether the spindle motor has substantially ceased rotating before executing the braking operation, where the difference value corresponds to T 2min −T 1min .