In PS7 DDR configuration,
effective DRAM bus width selected with 16 bit
when ECC is enabled, DQ is [31:0] and DQS is 3 to 0.
when ECC is disabled, DQ is [15:0] and DQS is 1 to 0.
if it means ECC active four DDR chips but DRAM bus width still is 16 bit?
That is correct.