Chien-search system employing a clock-gating scheme to save power for error correction decoder and other applications
Chien search apparatus operative to evaluate an error locator polynomial having a known rank and including a sequence of terms for each element in a finite field whose elements correspond respectively to bits in each of a stream of data blocks to be decoded, the apparatus comprising a sequence of functional units each operative to compute a corresponding term in the sequence of terms included in the error locator polynomial, each term having a degree; and a power saving unit operative to de-activate at least one individual functional unit from among the sequence of functional units, the individual functional unit being operative, when active, to compute a term whose degree exceeds the rank.
1. A Chien search apparatus operative to evaluate an error locator polynomial having a known rank and including a sequence of terms for each element in a finite field whose elements correspond respectively to bits in each of a stream of data blocks to be decoded, the apparatus comprising:
a sequence of functional units each operative to compute a corresponding term in said sequence of terms included in the error locator polynomial, each term having a degree; and
a power saving unit operative to de-activate at least one individual functional unit from among said sequence of functional units, said individual functional unit being operative, when active, to compute a term whose degree exceeds said rank;
wherein said power saving unit comprises multiple power saving logics, each power saving logic is arranged to selectively deactivate an individual subset of said functional units if all functional units in said individual subset are operative to compute terms whose degree exceeds said rank;
wherein each subset of said functional units comprises functional units that are arranged to compute terms having degrees that form a continuous sequence of degrees.
2. The apparatus according to claim 1 wherein each power saving logic comprises a clock gating unit controlling a provision of a clock signal to an individual subset of said functional units that is associated with the power saving logic.
3. The apparatus according to claim 2 wherein said clock gating unit defines a plurality of clock domains, wherein each of said sequence of functional units belongs to at least one of said clock domains.
4. The apparatus according to claim 1 further comprising a single adder that is coupled to each functional unit of the sequence of functional units; wherein the single adder and the sequence of functional units are arranged to calculate a single value of an error locator polynomial.
5. The apparatus according to claim 1 wherein the multiple power saving logics consists of two power saving logics.
6. The apparatus according to claim 1 wherein the multiple power saving logics consists of three power saving logics.
7. The apparatus according to claim 1 wherein said data blocks are BCH-encoded.
8. The apparatus according to claim 1 wherein said data blocks are Reed-Solomon-encoded.
9. The apparatus according to claim 1 wherein said data blocks are stored in a flash memory device.
10. The apparatus according to claim 1 and also comprising an error locator polynomial generator operative to generate said error locator polynomial and output its rank to said power saving unit.
11. The apparatus according to claim 1 , wherein different subsets of functional units comprise different numbers of functional units.
12. The apparatus according to claim 1 , wherein the sequence of functional units comprises fifty nine functional units;
wherein the multiple power saving logics comprise a first power saving logic and a second power saving logic;
wherein the first power saving logic controls the first subset of functional units that comprises a first till nineteenth functional units arranged to compute terms of first till nineteenth degrees; and
wherein the second power saving logic controls the second subset of functional units that comprises a twentieth first fifty ninth functional units arranged to compute terms of twentieth first till fifty ninth degrees.
13. The apparatus according to claim 1 , wherein the sequence of functional units comprises fifty nine functional units;
wherein the multiple power saving logics comprise a first power saving logic, a second power saving logic and a third power saving logic;
wherein the first power saving logic controls the first subset of functional units that comprises a first till tenth functional units arranged to compute terms of first till tenth degrees; and
wherein the second power saving logic controls the second subset of functional units that comprises an eleventh till twentieth functional units arranged to compute terms of eleventh till twentieth degrees;
wherein the third power saving logic controls the third subset of functional units that comprises a twenty first till fifty ninth functional units arranged to compute terms of twenty first till fifty ninth degrees.
14. A Chien search method operative to evaluate an error locator polynomial having a known rank and including a sequence of terms for each element in a finite field whose elements correspond respectively to bits in each of a stream of data blocks to be decoded, the method comprising: providing a sequence of functional units each operative to compute a corresponding term in the error locator polynomial, each term having a degree; and de-activating an individual subset of said functional units, by a power saving logic associated with the individual subset, if all functional units in said individual subset are operative to compute terms whose degree exceeds said rank; wherein each subset of said functional units comprises functional units that are arranged to compute terms having degrees that form a continuous sequence of degrees; wherein the sequence of functional units comprises multiple subsets of said functional unit and each subset of said functional units is associated with a single power saving logic.
15. The method according to claim 14 wherein a histogram of the number of errors per data block in said stream is known, said method also comprising designing power saving logic operative to effect said de-activating, including selecting, for each predetermined subset, a cut-off point in said sequence of functional units above which all functional units belong to said predetermined subset, wherein said cut-off point is selected to maximize power saving achieved by said de-activating, given said histogram.
16. The method according to claim 14 , wherein different subsets of functional units comprise different numbers of functional units.
17. The method according to claim 14 , wherein the sequence of functional units comprises fifty nine functional units;
wherein the multiple power saving logics comprise a first power saving logic and a second power saving logic;
wherein the first power saving logic controls the first subset of functional units that comprises a first till nineteenth functional units arranged to compute terms of first till nineteenth degrees; and
wherein the second power saving logic controls the second subset of functional units that comprises a twentieth first fifty ninth functional units arranged to compute terms of twentieth first till fifty ninth degrees.
18. The method according to claim 14 , wherein the sequence of functional units comprises fifty nine functional units;
wherein the multiple power saving logics comprise a first power saving logic, a second power saving logic and a third power saving logic;
wherein the first power saving logic controls the first subset of functional units that comprises a first till tenth functional units arranged to compute terms of first till tenth degrees; and
wherein the second power saving logic controls the second subset of functional units that comprises an eleventh till twentieth functional units arranged to compute terms of eleventh till twentieth degrees;
wherein the third power saving logic controls the third subset of functional units that comprises a twenty first till fifty ninth functional units arranged to compute terms of twenty first till fifty ninth degrees.