Function secded_check_byte 

pub fn secded_check_byte(word: usize) -> usize

The ECC lane holding word w’s check byte: bus byte 64 + 7 − w. The controller’s 576-bit word is either the memory burst’s eight beats of 72 DQ pins each (bus bit i on pin i mod 72), or its eight beats of the 64 data pins beneath the eight beats of the eight ECC pins (data bit i on pin i mod 64, ECC bit e on pin 64 + e mod 8). Under either, word w‘s data bits and ECC lane 7 − w lie on 72 different pins, so a failing pin flips one bit of each codeword, which the code corrects; pairing word w with lane w holds only under the second. Were the bus word each group of eight pins’ beats in turn, no grouping of whole bytes would hold under all three.