The DBI pins need to be centered for the same
reason as the DQ pins. A small DBI margin affects the validity of the entire byte
line.
This is accomplished as follows:
- A toggling data pattern is written that will create a 101010 pattern on the DBI pin. Delay the DBI if the toggling pattern is not observed.
- After the toggling pattern is detected, continue to shift the DBI until the noise region is found. This establishes the left margin.
- Remove the left margin taps, and increment the clock strobe until the noise region is found. This esablishes the right margin.
- Revert the clock strobe delays, and compare left and right margins to determine the ideal centering.