Position determination using circular shift codes
View Patent ↗A shift code that consists of N-symbol code words is provided as an L-symbol “master sequence” in which no sub-sequence of N symbols repeats, where L≦S N and S is the number of code symbols. A decoder determines a location in the code from N decoded symbols. The code locations may, for example, correspond to radial positions, or other position, times, and so forth. In one embodiment, the master sequence is continuously written to a data storage disk during a spiral write operation and a reader on a given circular track reads at least N symbols from the portion of the spiral that crosses the track and determines a code word. The radial position of the reader is then determined based on the location of the code word in the code.
1. A method comprising utilizing a data writer to write a sequence that corresponds to a code with N-symbol code words, the sequence having L symbols with every N-symbol subsequence being non-repeating; and determining a location in the code by decoding an N-symbol code word.
2. The method of claim 1 wherein the code is circular and the step of providing includes providing at the end of the sequence at least one symbol from the beginning of the sequence.
3. The method of claim 1 wherein the location in the code corresponds to a radial position.
4. A method comprising: writing to respective radial positions portions of a master sequence that corresponds to a code with N-symbol code words, the sequence having L symbols in which every N-symbol subsequence is non-repeating; reading at least N symbols of the master sequence from a radial position and determining a code word; determining the radial position based on the location of the code word in the code, and wherein the step of writing portions of the master sequence is a spiral write operation from one diameter of a data storage disk to another diameter of the disk, in which the master sequence is repeatedly written.
5. The method of claim 4 wherein the step of reading is reading from a spiral at a constant radial position.
6. The method of claim 4 wherein the sequence corresponds to a code of length L with N-symbol code words in which the code words overlap by N−1 symbols, and any N symbols of the master sequence produce a code word.
7. The method of claim 6 wherein the code is circular.
8. The method of claim 4 wherein the radial position of the reader is relative to a range of tracks on the disk.
9. The method of claim 4 further including a step of detecting an error if the next symbol read is not the next expected symbol in the master sequence.
10. The method of claim 9 further including a step of correcting the error based on additional symbols read from the radial position.
11. The method of claim 5 further including a step of determining fine position information based on a location of a read envelope peak relative to the code word symbols.
12. A disk including a plurality of tracks; and a spiral write pattern consisting of a repeated master sequence of a shift code with code words written in spiral crossings of the respective tracks.
13. The disk of claim 12 wherein the code words of the shift code consist of N symbols; and there are no repeating patterns of N symbols in the master sequence.
14. The disk of claim 13 wherein the code words of the shift code overlap; and the master sequence consists of the non-overlapping symbols of a plurality of adjacent code words.
15. The disk of claim 14 wherein the code words overlap by N−1 symbols, and any N symbols of the master sequence produce a code word.
16. The disk of claim 12 wherein the radial position of the reader is relative to a range of tracks on the disk.
17. The disk of claim 12 wherein the shift code is circular.