Read Centering (Complex) - 1.0 English

Calibration Overview

Complex data patterns are used for advanced read DQS centering for memory systems to improve read timing margin. Long and complex data patterns on both the victim and aggressor DQ lanes impact the size and location of the data eye. The objective of the complex calibration step is to generate the worst case data eye on each DQ lane so that the DQS signal can be aligned, resulting in good setup/hold margin during normal operation with any workload.

There are two long data patterns stored in a block RAM, one for a victim DQ lane, and an aggressor pattern for all other DQ lanes. These patterns are used to generate write data, as well as expected data on reads for comparison and error logging. Each pattern consists of 157 8-bit chunks or BL8 bursts.

Each DQ lane of 1-byte takes a turn at being the victim. An RTL state machine automatically selects each DQ lane in turn, MUXing the victim or aggressor patterns to the appropriate DQ lanes, issues the read/write transactions, and records errors. The victim pattern is only walked across the DQ lanes of the selected byte to be calibrated, and all other DQ lanes carry the aggressor pattern, including all lanes in unselected bytes if there is more than 1-byte lane.

Similar steps to those described in Read DQS Centering are performed, with the PQTR/NQTR starting out at the left edge of the simple window found previously. The complex pattern is written and read back. All bits in a nibble are checked to find the left edge of the window, incrementing the bits together as needed or the PQTR/NQTR to find the aggregate left edge. After the left and right edges are found, it steps through the entire data eye.

CAL_ERROR Decode for Read DQS to DQ/DBI Centering Complex Calibration

The status of Read DQS to DQ/DBI Centering Complex can also be determined by decoding the CAL_ERROR result according to the table below.