Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
449
UG586 November 30, 2016
Chapter 3:
RLDRAM II and RLDRAM 3 Memory Interface Solutions
If performing write calibration for RLDRAM 3, you can calibrate reads first by using the
Read-Training Register (RTR) of the DRAM. This provides a clock-like pattern from the
DRAM that does not require writing in a pattern first. All other times a pattern of
"0F0F_0FF0" is used to calibrate read clock and data capture.
If performing write calibration for RLDRAM II, this stage of calibration is continually
restarted based on the requirements on the write calibration algorithm.
The calibration logic reads data out of the IN_FIFO and records it for comparison. The
calibration logic checks for the sequence of the data pattern read, to determine the
alignment of the clock with respect to the data. No assumption is made about the initial
relationship between the capture clock and the data window at tap 0 of the fine delay line.
The algorithm tries to align the clock to the left edge of the data window, by delaying the
read data through the IDELAY element.
Next, the clock is delayed using the PHASER taps and centered within the corresponding
data window. The PHASER_TAP resolution is based on the FREQ_REF_CLK period, and the
per-tap resolution is equal to (FREQ_REFCLK_PERIOD/2)/64 ps. For memory interface
frequencies
≥
400 MHz, using the maximum of 64 PHASER taps can provide a delay of one
data period or one-half the clock period. This enables the calibration logic to accurately
center the clock within the data window.
shows this example.