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The ECC algorithm is a multiple parity bit accumulation computed on the odd and even bit streams extracted from the byte or Word16 streams. The parity accumulation is split into row and column accumulations, as shown in Figure 12-1641 and Figure 12-1642. The intermediate row and column parities are used to compute the upper level row and column parities. Only the final computation of each parity bit is used for ECC comparison and correction.
P1o = bit7 XOR bit5 XOR bit3 XOR bit1 on each byte of the data stream
P1e = bit6 XOR bit4 XOR bit2 XOR bit0 on each byte of the data stream
P2o = bit7 XOR bit6 XOR bit3 XOR bit2 on each byte of the data stream
P2e = bit5 XOR bit4 XOR bit1 XOR bit0 on each byte of the data stream
P4o = bit7 XOR bit6 XOR bit5 XOR bit4 on each byte of the data stream
P4e = bit3 XOR bit2 XOR bit1 XOR bit0 on each byte of the data stream
Each column parity bit is XORed with the previous accumulated value.
For line parities, the bits of each new data are XORed together, and line parity bits are computed as described below:
P8e = row0 XOR row2 XOR row4 XOR ... XOR row254
P8o = row1 XOR row3 XOR row5 XOR ... XOR row255
P16e = row0 XOR row1 XOR row4 XOR row5 XOR ... XOR row252 XOR row 253
P16o = row2 XOR row3 XOR row6 XOR row7 XOR ... XOR row254 XOR row 255
Unused parity bits in the result registers are set to 0.
Figure 12-1643 shows ECC computation for a 256-byte data stream (read or write). The result includes six column parity bits (P1o-P2o-P4o for odd parities, and P1e-P2e-P4e for even parities) and sixteen row parity bits (P8o-P16o-P32o--P1024o for odd parities, and P8e-P16e-P32e--P1024e for even parities).
Figure 12-1644 shows ECC computation for a 512-byte data stream (read or write). The result includes six column parity bits (P1o-P2o-P4o for odd parities, and P1e-P2e-P4e for even parities) and eighteen row parity bits (P8o-P16o-P32o--P1024o- - P2048o for odd parities, and P8e-P16e-P32e--P1024e- P2048e for even parities).
For a 2-KB page, four 512 bytes ECC calculations plus 1 for the spare area are required. Results are stored in the GPMC_ECCj_RESULT registers (where j = 1 to 9).