Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
158
UG586 November 30, 2016
Chapter 1:
DDR3 and DDR2 SDRAM Memory Interface Solution
IMPORTANT:
Customers using the PHY only design must include the periodic read logic within the
custom controller.
If the periodic reads are not included, two things can occur that might cause issues:
1. The free running PHASER_IN ICLK drifts away from
DQS
. This exposes the memory
system to issues when ICLK switches.
2. Read latency adjustments are not done within the phaser. This causes issues with the
switching logic in the PHASER_IN.
The periodic read was added in MIG core v1.5, released with ISE Design Suite 14.1. Further
characterization work proved the 1 µs periodic read was required to keep the PHASER_IN
aligned and ready for subsequent reads.
IMPORTANT:
The frequency of the periodic reads must be 1 µs and cannot be changed.
Temperature Monitor
The temperature monitor helps maintain
DQS
center alignment in the data valid window by
compensating for temperature drift.
The temperature monitor is comprised of two modules. The first module,
tempmon
,
instantiates the XADC module and periodically samples it for the current device
temperature. The tempmon configures the XADC for continuous looping on the XADC
calibration and temperature measurement, both with averaging. This generates an updated
temperature measurement every 116 µs. The
tempmon
module resides within the clocking
infrastructure. The module also synchronizes the parallel temperature bus to the Memory
Controller FPGA logic clock.
The XADC instantiation can be bypassed if the user design already instantiates the XADC.
This selection is configured by a selection in the MIG GUI. In this case, you must drive and
periodically update the device_temp_i[11:0]. It should be updated at a minimum of once
every 116 µs and there is no limit on the maximum update rate. Although updates are more
frequent, the REF rate is not affected. The
device_temp_i[11:0]
value is the raw value
as read from the DRP port defined by the XADC specification
XADC Wizard v2.4 LogiCORE
IP Product Guide
(PG091)
, without any conversion. XADC averaging must be turned
on for the temperature channel. Averaging can be turned on only for the temperature if
averaging is not desired for the other channels. Averaging should be set to 16, but 64 or
256 is acceptable if already set for other XADC channels.