Xilinx System Generator V2.1 Reference Manual page 98

Xilinx System Generator v2.1 Reference Guide
The block parameters dialog box can be invoked by double-clicking the icon in your
Simulink model.
Figure 3-68: Gateway In block parameters dialog box
Parameters specific to the Gateway In block are:
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IOB Timing Constraint: In hardware, a Gateway In is realized as a set of
input/output buffers (IOBs). There are three ways to constrain the timing on
IOBs. They are None , Data Rate , and Data Rate, Set 'FAST'
Attribute .
If None is selected, no timing constraints for the IOBs are put in the user
constraint file (.ucf) produced by System Generator. This means the paths from
the IOBs to synchronous elements are not constrained.
If Data Rate is selected, the IOBs are constrained at the data rate at which the
IOBs operate. The rate is determined by the System Clock Period provided on the
System Generator block and the sample rate of the Gateway relative to the other
sample periods in the design. For example, the following OFFSET = IN
constraints are generated for a Gateway In named 'Din' that is running at the
system period of 10 ns:
# Offset in constraints
NET "Din<0>" OFFSET = IN : 10.0 : BEFORE "clk";
NET "Din<1>" OFFSET = IN : 10.0 : BEFORE "clk";
NET "Din<2>" OFFSET = IN : 10.0 : BEFORE "clk";
NET "Din_valid" OFFSET = IN : 10.0 : BEFORE "clk";
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