In this stage, bursts of complex pattern
are written to the memory and read back. The comparison results of the read data with
the expected data is recorded in a cal comparison status register. The rise and fall
nibble wise comparison results are available to the calibration algorithm. Based on
these comparison results the algorithm decides on which taps to manipulate.
The complex read calibration steps are listed as follows:
- Revert PQTR and NQTR delays to 0 for all read clocks and its inverse clocks.
- Check whether the read clock and its inverse clock samples the noise region of the data.
- If either of the clocks samples the valid region of the data, then DQ and DM IDELAY taps are incremented together until both clocks start sampling the noise region.
- The read clock and its inverse are moved using PQTR and NQTR taps to traverse the data window from noise to valid region and then valid region to noise. The delays taps difference between the noise to valid crossing point and the valid to noise crossing point is called the valid window. The read clock and its inverse is centered in their respective valid windows thereby completing complex read calibration.