Two-level error correction encoder

Abstract

A two-level error correction encoder encodes m-bit data symbols in a first level of encoding in accordance with a distance d ECC over GF(2.sup.m+i) to produce (m+i)-bit ECC redundancy symbols and, during a second level of encoding, both modifies the set of ECC redundancy symbols, as necessary, to set i selected bits in each symbol in a predetermined truncation pattern and appends to the set of ECC symbols one or more pseudo redundancy symbols. The encoder includes d-1 Galois Field multipliers, and d-1 associated redundancy-symbol registers and an ECC symbol modifier lookup table that has stored therein information that the encoder uses during the second level of encoding. After the first level of encoding, the d-1 registers contain the (m+i)-bit ECC redundancy symbols. These symbols are used to enter the look-up table and select information that the encoder then encodes along with the ECC redundancy symbols, to produce the modified ECC redundancy symbols and append thereto one or more pseudo redundancy symbols. As the ECC redundancy symbols are modified, the encoding system removes them from the two-level encoder and appends them to the data. The last symbol(s) removed from the encoder and appended to the data are the one or more pseudo redundancy symbols. The system then truncates the i-bit pattern from each of the redundancy symbols to produce, at the end of the two-level encoding operation, a data code word that includes the m-bit data symbols, the m-bit modified ECC redundancy symbols and one or more m-bit pseudo redundancy symbols.