SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
The ECC (or remainder) is presented by the BCH module as a single 104-bit (or 52-bit), little-endian vector. Software must fetch those 13 bytes (or 6 bytes) from the module interface and then store them to the spare area (page write) in the NAND or to an intermediate buffer for comparison with the stored ECC (page read). There are no constraints on the ECC mapping inside the spare area: it is software-controlled.
It is advised, however, to maintain a coherence in the respective formats of the message or the ECC remainder once they have been read out of the NAND. The error correction algorithm works from the complete codeword (concatenated message and remainder) once an error is detected. The creation of this codeword must be made as straightforward as possible.
There are cases in which the same NAND access contains both data and the ECC protecting that data. This is the case when the data/ECC boundary (which can be on any nibble) does not coincide with an access boundary. The ECC is calculated on the fly following the write. In that case, the write must also contain part of the ECC because it is impossible to insert the ECC on the fly. Instead: