SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
The following rules apply to the entire mapping description:
Each of the following sections gives a NAND page mapping example (per-sector spare mappings, pooled spare mapping, per-sector spare mapping, with ECC separated at the end of the page).
In the mapping diagrams, sections that belong to the same BCH codeword have the same color (blue or green); unprotected sections are not covered (orange) by the BCH scheme.
Below each mapping diagram, a write (encoding) and read (decoding: syndrome generation) sequence is given, with the number of the active buffers at each point in time (yellow). In the inactive zones (grey), no computing is taking place but the data counter is still active.
In Figure 12-2112 through Figure 12-2114, the tables on the left summarize the mode, size0, and size1 parameters to program for, respectively, write and read processing of a page, with the given mapping, where:
Each time the processing of a BCH block is complete (ECC calculation for write/encoding, syndrome generation for read/decoding, indicated by red arrows), the update pointer is pulsed. The processing for block 0 can be the first or the last to complete, depending on the NAND page mapping and operation (read or write). All examples show a page size of 1 KB + spares; that is, S = 2 sectors of 512 bytes. The same principles can be extended to larger pages by adding more sectors.
The actual BCH codeword size is used during the error location work to restrict the search range: by definition, errors can happen only in the codeword that was actually written to the NAND, not in the mathematical codeword of n = 213 – 1 = 8191 bits; that codeword (higher-order bits) is all-zero and implicit during computations.
The actual BCH codeword size depends on the mode, the programmed sizes, and the sector number (all sizes in nibbles):