Xilinx V2.1 manual Xilinx System Generator v2.1 Reference Guide, Xilinx Development System

Models: V2.1

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Parameters specific to the Gateway Out block are:

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 3-69: Gateway Out block parameters dialog box

Parameters specific to the Gateway Out block are:

IOB Timing Constraint: input/output buffers (IOBs). IOBs. They are None, Data Attribute.

In hardware, a Gateway Out is realized as a set of There are three ways to constrain the timing on Rate, and Data Rate, Set 'FAST'

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 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 = OUT constraints are generated for a Gateway Out named 'Dout' that is running at the system period of 10 ns:

# Offset out constraints

NET "Dout<0>" OFFSET = OUT : 10.0 : AFTER "clk";

NET "Dout<1>" OFFSET = OUT : 10.0 : AFTER "clk";

NET "Dout<2>" OFFSET = OUT : 10.0 : AFTER "clk";

NET "Dout_valid" OFFSET = OUT : 10.0 : AFTER "clk"; NET "Dout_valid" FAST;

It should be noted there is a valid bit that accompanies the data signal. It is constrained at the same rate. For more information concerning the valid bit, refer to the Hardware Handshaking section in Chapter 1 of this manual.

If Data Rate, Set 'FAST' Attribute is selected, the OFFSET = OUT constraints described above are produced. In addition, a FAST slew rate attribute is generated for each IOB. This reduces delay but increases noise and power consumption. For the previous example, the following additional attributes are added to the .ucf file

NET "Dout<0>" FAST;

NET "Dout<1>" FAST;

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Xilinx V2.1 manual Xilinx System Generator v2.1 Reference Guide, Parameters specific to the Gateway Out block are