This training is to center align the Write MDQS in the Write MDQ window at the DRAM. In this training mode, host pre-programs the DB MPR registers with the expected pattern, issues the write commands to load the data into memory, and issues the reads to the memory. Data buffer would compare the read data with the expected data and feeds the result on to the DQ bus. Calibration finds the left and right edges of the valid window and centers it.