Unified time base for storage device data channel
A method of clocking a data channel of a storage device includes generating a single time-base frequency signal, deriving from the single time-base frequency signal, using a plurality of frequency-modification techniques, a plurality of individual clock signals, each respective one of the individual clock signals being for clocking a respective one of reading, writing and servo functions of the data channel. When the storage device is a disk storage device having a rotational frequency, generating a single time-base frequency signal may include generating a time-base frequency signal based on the rotational frequency. Deviation of the single time-base frequency from the rotational frequency may be detected, and the deviation may be compensated for. Each technique of the frequency-modification techniques may be a digital frequency-modification technique, such as a digital timing recovery technique or a digital frequency division technique.
1. A method of clocking a data channel of a disk storage device having a rotational frequency, the method comprising:
generating a single time-base frequency signal based on the rotational frequency;
deriving from the single time-base frequency signal, using a plurality of digital frequency-modification techniques, a plurality of individual clock signals, each respective one of the individual clock signals being for clocking a respective one of reading, writing and servo functions of the data channel, wherein:
one of the digital frequency-modification techniques is a write pattern frequency modification technique requiring bit repetition for modification of a write phase; the method further comprising:
oversampling the time-base frequency in portions of the data channel to provide the bit repetition.
2. The method of clocking a data channel according to claim 1 further comprising:
detecting a deviation of the single time-base frequency from the rotational frequency; and
compensating for the deviation.
3. The method of clocking a data channel according to claim 2 wherein:
detecting the deviation of the single time-base frequency from the rotational frequency comprises detecting a time interval between servo wedges; and
compensating for the deviation comprises:
determining a scale factor based on a relationship of the deviation to a period of the single time-base frequency, and
applying the scale factor to each individual clock signal in the plurality of clock signals.
4. The method of clocking a data channel according to claim 2 wherein:
detecting a deviation of the single time-base frequency from the rotational frequency comprises detecting a servo sync mark at a time other than a time expected based on the rotational frequency; and
compensating for the deviation comprises deriving a phase differential from the deviation and applying the phase differential to the single time-base frequency.
5. The method of clocking a data channel according to claim 2 wherein:
detecting a deviation of the single time-base frequency from the rotational frequency comprises detecting a skipped clock using digital timing recovery; and
compensating for the deviation comprises deriving a phase differential from the deviation and applying the phase differential to the single time-base frequency.
6. The method of clocking a data channel according to claim 1 further comprising adjusting a write pattern frequency on a per-sector basis to account for variations in disk surface quality.
7. The method of clocking a data channel according to claim 1 wherein one of the digital frequency-modification techniques is a digital timing recovery technique.
8. The method of clocking a data channel according to claim 1 wherein one of the digital frequency-modification techniques is a digital frequency division technique.
9. A storage device, comprising:
a storage disk, having a rotational frequency, on which data is written; and
a data channel including clock circuitry, the clock circuitry comprising:
circuitry configured to generate a single time-base frequency signal based on the rotational frequency, and
digital frequency-modification circuitry configured to derive from the single time-base frequency signal, using a plurality of digital frequency-modification techniques, a plurality of individual clock signals, each respective one of the individual clock signals being for clocking a respective one of reading, writing and servo functions of the data channel, wherein the digital frequency-modification circuitry comprises:
oversampling circuitry to provide bit repetition in the time-base frequency in portions of the data channel, and
write pattern frequency modification circuitry configured to operate on repetitive bits to modify a write phase.
10. The storage device of claim 9 wherein the circuitry configured to generate a single time-base frequency signal comprises a phase-locked loop.
11. The storage device of claim 9 further comprising:
circuitry configured to detect a deviation of the single time-base frequency from the rotational frequency; and
circuitry configured to compensate for the deviation.
12. The storage device of claim 11 wherein:
the circuitry configured to detect the deviation of the single time-base frequency from the rotational frequency comprises circuitry configured to detect a time interval between servo wedges; and
the circuitry configured to compensate for the deviation comprises:
circuitry configured to determine a scale factor based on a relationship of the deviation to a period of the single time-base frequency, and
circuitry configured to apply the scale factor to each individual clock signal in the plurality of clock signals.
13. The storage device of claim 11 wherein:
the circuitry configured to detect the deviation of the single time-base frequency from the rotational frequency comprises circuitry configured to detect a servo sync mark at a time other than a time expected based on the rotational frequency; and
the circuitry configured to compensate for the deviation comprises circuitry configured to derive a phase differential from the deviation and to apply the phase differential to the single time-base frequency.
14. The storage device of claim 11 wherein:
the circuitry configured to detect the deviation of the single time-base frequency from the rotational frequency comprises circuitry configured to detect a skipped clock using digital timing recovery; and
the circuitry configured to compensate for the deviation comprises circuitry configured to derive a phase differential from the deviation and to apply the phase differential to the single time-base frequency.
15. The storage device of claim 9 wherein the write pattern frequency modification circuitry is further configured to adjust a write pattern frequency on a per-sector basis to account for variations in disk surface quality.
16. The storage device of claim 9 wherein the digital frequency-modification circuitry comprises digital timing recovery circuitry.
17. The storage device of claim 9 wherein the digital frequency-modification circuitry comprises digital frequency division circuitry.