Xilinx Zynq-7000 User Manual page 171

X-Ref Target - Figure 1-83
A user-refresh operation can be performed any time provided the handshake defined above
is followed. There are no additional interfacing requirements with respect to other
commands. However, pending requests affect when the operation goes out. The Memory
Controller fulfills all pending data requests before issuing the refresh command. Timing
parameters must be considered for each pending request when determining when to strobe
app_ref_req to avoid a tREFI violation. To account for the worst case, subtract tRCD, CL,
the data transit time, and tRP for each bank machine to ensure that all transactions can
complete before tREFI expires.
tREFI
(
A user REF should be issued immediately following calibration to establish a time baseline
for determining when to send subsequent requests.
User ZQ
For user-controlled ZQ calibration, the Memory Controller managed maintenance should
be disabled by setting the tZQI parameter to 0.
To request a ZQ command, app_zq_req is strobed for one cycle. When the Memory
Controller sends the command to the PHY, it strobes app_zq_ack for one cycle, after
which another request can be sent.
X-Ref Target - Figure 1-84
A user ZQ operation can be performed any time provided the handshake defined above is
followed. There are no additional interfacing requirements with respect to other commands.
However, pending requests affect when the operation goes out. The Memory Controller
fulfills all pending data requests before issuing the ZQ command. Timing parameters must
be considered for each pending request when determining when to strobe app_zq_req to
achieve the desired interval if precision timing is desired.
Zynq-7000 AP SoC and 7 Series FPGAs MIS v4.1
UG586 November 30, 2016
Chapter 1: DDR3 and DDR2 SDRAM Memory Interface Solution
Figure 1-83: User-Refresh Interface
Equation 1-1
tRCD CL 4 tCK
( ( ( ) ×
– + +
Figure 1-84
Figure 1-84: User ZQ Interface
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shows the REF request interval maximum.
tRP nBANK_MACHS
) ) ×
+
illustrates the interface.
)
Equation 1-1
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