Xilinx V2.1 Uživatelský manuál stáhnout pdf (Strana 98)

98 Xilinx Development System

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:

• 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

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.

Data Rate

is selected, the IOBs are constrained at the data rate at which the

IOBs operate. The rateis determined by theSystem ClockPeriod 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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Xilinx V2.1 Uživatelský manuál Strana 98