Preamble acquisition without second order timing loops

1. A method of performing timing acquisition, including:

sampling a first portion of a preamble having an end;

using a processor to determine a first phase value based on the sampled first portion;

sampling a second portion of the preamble;

using the processor to determine a second phase value based on the sampled second portion;

using the processor to extrapolate a future end phase value, corresponding to a future end sample of the preamble that has not yet been sampled, based at least in part the first phase value and the second phase value where the first phase value, the second phase value, and the future end phase value all correspond to the same preamble; and

adjusting a clock using the extrapolated end phase value.

2. A method as recited in claim 1 , wherein the preamble is associated with a segment stored on a magnetic disk.

3. A method as recited in claim 1 , wherein at least one of the first phase value, the second phase value, the end phase value, and the end frequency value is an offset.

4. A method as recited in claim 1 , wherein the first portion and the second portion do not overlap.

5. A method as recited in claim 1 , wherein the first portion has a length that is a positive integer multiple of 4T.

6. A method as recited in claim 1 , wherein the number of portions of the preamble for which a phase value is determined and is used in extrapolating is based on the length of the preamble.

7. A method as recited in claim 1 , wherein the number of portions of the preamble for which a phase value is determined and is used in extrapolating is based on the length of the preamble, and this is described in a lookup table (LUT).

8. A method as recited in claim 1 , wherein determining the first phase value includes performing at least one of the following: estimating the first phase value, using a lookup table (LUT), or using an arctangent.

9. A method as recited in claim 1 , wherein extrapolating includes performing at least one of the following: using linear regression, using precomputed coefficients, or using precomputed coefficients that account for a priori information.

10. A method as recited in claim 1 , wherein a shared processor is used and the end phase value is extrapolated first and the end frequency value is extrapolated next, or vice versa.

11. A method as recited in claim 1 , wherein the first, second, and future end phase values are phase offset values and extrapolating a future end phase offset value includes:

determining a line based at least in part on: (1) a first data point comprising: (a) a first sample number corresponding to the first sampled portion of the preamble and (b) the first phase offset value and (2) a second data point comprising: (a) a second sample number corresponding to the second sampled portion of the preamble and (b) the second phase offset value; and

setting the future end phase offset value to be the value of the line at the future end sample of the preamble.

12. A method as recited in claim 11 further comprising:

determining a frequency offset based at least in part on the slope of the line; and

adjusting the clock using the frequency offset.

13. A system for performing timing acquisition, including:

a sampler configured to sample a first portion of a preamble having an end and sample a second portion of the preamble;

a processor configured to:

determine a first phase value based on the sampled first portion;

determine a second phase value based on the sampled second portion; and

extrapolate a future end phase value, corresponding to a future end sample of the preamble that has not yet been sampled, based at least in part the first phase value and the second phase value where the first phase value, the second phase value, and the future end phase value all correspond to the same preamble; and

a controller configured to adjust a clock using the extrapolated end phase value.

14. A system as recited in claim 13 , wherein the first, second, and future end phase values are phase offset values and extrapolating a future end phase offset value includes:

determining a line based at least in part on: (1) a first data point comprising: (a) a first sample number corresponding to the first sampled portion of the preamble and (b) the first phase offset value and (2) a second data point comprising: (a) a second sample number corresponding to the second sampled portion of the preamble and (b) the second phase offset value; and

setting the future end phase offset value to be the value of the line at the future end sample of the preamble.

15. A method as recited in claim 14 , wherein:

the processor is further configured to determine a frequency offset based at least in part on the slope of the line; and

the controller is further configured to adjust the clock using the frequency offset.

16. A computer program product for performing timing acquisition, the computer program product being embodied in a computer readable medium and comprising computer instructions for:

sampling a first portion of a preamble having an end;

determining a first phase value based on the sampled first portion;

sampling a second portion of the preamble;

determining a second phase value based on the sampled second portion;

extrapolating a future end phase value, corresponding to a future end sample of the preamble that has not yet been sampled, based at least in part the first phase value and the second phase value where the first phase value, the second phase value, and the future end phase value all correspond to the same preamble; and

adjusting a clock using the extrapolated end phase value.

17. A computer program product as recited in claim 16 , wherein the first, second, and future end phase values are phase offset values and extrapolating a future end phase offset value includes:

determining a line based at least in part on: (1) a first data point comprising: (a) a first sample number corresponding to the first sampled portion of the preamble and (b) the first phase offset value and (2) a second data point comprising: (a) a second sample number corresponding to the second sampled portion of the preamble and (b) the second phase offset value; and

setting the future end phase offset value to be the value of the line at the future end sample of the preamble.

18. A method as recited in claim 17 further comprising computer instructions for:

determining a frequency offset based at least in part on the slope of the line; and

adjusting the clock using the frequency offset.

19. A method of performing timing acquisition, including:

using a processor to determine a first phase value based on a first portion of a preamble;

gradually adjusting a clock based at least in part on the first phase value, wherein gradually adjusting includes changing a setting of the clock at least two times;

using a processor to determine a second phase value based a second portion of the preamble, wherein the second portion includes the first portion;

determining, at a point in time after the gradual adjustment of the clock based at least in part on the first phase value has started, how much gradual clock adjustment has been accomplished; and

gradually adjusting the clock based at least in part on the second phase value and taking into consideration how much gradual clock adjustment has been accomplished, wherein gradually adjusting includes changing a setting of the clock at least two times.

20. A method as recited in claim 19 , further including:

determining an end frequency value based at least in part the first phase value and the second phase value; and

adjusting the clock using the extrapolated end frequency value.

21. A method as recited in claim 19 , wherein the preamble is associated with a segment stored on a magnetic disk.

22. A method as recited in claim 19 , wherein at least one of the first phase value and the second phase value is an offset.

23. A method as recited in claim 19 , wherein the first portion and the second portion have lengths that are a positive integer multiple of 4T.

24. A method as recited in claim 19 , wherein the number of portions of the preamble for which a phase value is determined and is used in gradually adjusting is based on the length of the preamble.

25. A method as recited in claim 19 , wherein the number of portions of the preamble for which a phase value is determined and is used in gradually adjusting is based on the length of the preamble, and this is described in a lookup table (LUT).

26. A method as recited in claim 19 , wherein determining the first phase value includes performing at least one of the following: estimating the first phase value using a lookup table (LUT), using an arctangent, using linear regression, using precomputed coefficients, or using precomputed coefficients that account for a priori information.

27. A method as recited in claim 20 , wherein a shared processor is used and the second phase value is determined first and the end frequency value is determined next, or vice versa.

28. A method as recited in claim 19 , wherein:

gradually adjusting a clock based at least in part on the first phase value includes adjusting the clock a fixed amount at fixed intervals; and

determining an amount of the gradual clock adjustment that has been accomplished is based at least in part on (1) an amount of time that has elapsed since the gradual adjustment of the clock based at least in part on the first phase value started, (2) the fixed amount the clock is adjusted by, and (3) the fixed intervals the clock is adjusted at.

29. A system for performing timing acquisition, including:

a processor configured to:

determine a first phase value based on a first portion of a preamble;

determine a second phase value based a second portion of the preamble, wherein the second portion includes the first portion; and

determine, at a point in time after the gradual adjustment of the clock based at least in part on the first phase value has started, how much gradual clock adjustment has been accomplished; and

a controller configured to:

gradually adjust a clock based at least in part on the first phase value, wherein gradually adjusting includes changing a setting of the clock at least two times; and

gradually adjust the clock based at least in part on the second phase value and taking into consideration how much gradual clock adjustment has been accomplished, wherein gradually adjusting includes changing a setting of the clock at least two times.

30. A system as recited in claim 29 , wherein:

the controller is configured to gradually adjust a clock based at least in part on the first phase value by adjusting the clock a fixed amount at fixed intervals; and

the processor is configured to determine an amount of the gradual clock adjustment that has been accomplished is based at least in part on (1) an amount of time that has elapsed since the gradual adjustment of the clock based at least in part on the first phase value started, (2) the fixed amount the clock is adjusted by, and (3) the fixed intervals the clock is adjusted at.

31. A computer program product for performing timing acquisition, the computer program product being embodied in a computer readable medium and comprising computer instructions for:

determining a first phase value based on a first portion of a preamble;

gradually adjusting a clock based at least in part on the first phase value, wherein gradually adjusting includes changing a setting of the clock at least two times;

determining a second phase value based a second portion of the preamble, wherein the second portion includes the first portion;

determining, at a point in time after the gradual adjustment of the clock based at least in part on the first phase value has started, how much gradual clock adjustment has been accomplished; and

gradually adjusting the clock based at least in part on the second phase value and taking into consideration how much gradual clock adjustment has been accomplished, wherein gradually adjusting includes changing a setting of the clock at least two times.

32. A computer program product as recited in claim 31 , wherein:

gradually adjusting a clock based at least in part on the first phase value includes adjusting the clock a fixed amount at fixed intervals; and

determining an amount of the gradual clock adjustment that has been accomplished is based at least in part on (1) an amount of time that has elapsed since the gradual adjustment of the clock based at least in part on the first phase value started, (2) the fixed amount the clock is adjusted by, and (3) the fixed intervals the clock is adjusted at.