In the Quartus® II software version 12.1, when the UniPHY DDR3 IP configuration is for a single rank interface and meets these requirements, DQS tracking is enabled :
Stratix V, Arria V GZ. Memory clock frequency >= 750MHz
Arria V (GX, GT, SX, ST) : Memory clock frequency >= 534 MHz. For a -5 speed grade device when the memory clock frequency >= 450MHz.
During DQS tracking, the user's application will see a delay in obtaining DDR3 memory access.
There are two different types of delays :
1) DQS tracking samples : These occur after every memory refresh cycle and are memory reads. For a quarter rate interface this typically takes around 800ns.
2) DQS tracking updates : Once sufficient DQS tracking samples have been accumulated, an update to the DDR3 data path I/O delay settings occurs which results in a longer delay. DQS tracking updates take at least 4us and increase with the number of DQS groups in the interface.
If these delays do not affect your application, no change is required.
If these delays do affect your application, use the workaround below.