Locking a disk-locked clock using timestamps of successive servo address marks in a spiral servo track

A method for phase locking a system clock to servo address marks in a mass storage system having a rotating magnetic storage media and head over the media for reading data and servo information thereon, the rotating magnetic storage media having adjacent servo address marks written in a spiral pattern of servo address marks on the storage media, and a counter driven by a system clock, the method comprising the steps of:

• reading, by the head, a plurality of adjacent servo address marks each time the head encounters the spiral pattern of servo address marks;
• detecting each of adjacent servo address marks read by the head;
• sampling the counter, via a latch, to obtain a sampled count value each time a servo address mark is detected;
• calculating differences in value between successive sampled count values from the latch;
• averaging the differences in value to create an average difference value;
• normalizing a difference between the average difference value and a target value to create a phase error value;
• and updating a phase of the system clock in response to the phase error value.

A method for phase locking a system clock to servo address marks in a mass storage system having a rotating magnetic storage media and head over the media for reading data and servo information thereon, the rotating magnetic storage media having adjacent servo address marks written in a spiral pattern of servo address marks on the storage media, and a counter driven by a system clock, the method comprising the steps of:

• reading, by the head, a plurality of adjacent servo address marks each time the head encounters the spiral pattern of servo address marks;
• slicing signals from the head to generate sliced data;
• serially shifting the sliced data into a shift register;
• detecting a servo address mark when the sliced data in the shift register matches a pre-established bit pattern;
• sampling the counter, via a latch, to obtain a sampled count value each time a servo address mark is detected;
• calculating differences in value between successive sampled count values from the latch;
• averaging the differences in value to create an average difference value;
• normalizing a difference between the average difference value and a target value to create a phase error value;
• and
• updating a phase of the system clock in response to the phase error value;
• wherein the phase error is calculated in accordance with:
• (TARGET−AVE_SAMP DIFF)/TARGET;
• where TARGET is a desired average difference value when the system clock is locked to the servo address marks, and AVE_SAMP DIFF is an actual average difference count value.