MATLAB DESIGN HDL CODER RELEASE NOTES User's Guide download pdf (Page 37)

System Generator for DSP User Guide www.xilinx.com 37

UG640 (v 12.2) July 23, 2010

System-Level Modeling in System Generator

NaNs that drive a Gateway In become indeterminate values. System Generator provides

an Indeterminate Probe block that allows for the detection of indeterminate values. This

probe cannot be translated into hardware.

In System Generator, any arithmetic signal can be indeterminate, but Boolean signals

cannot be. If a simulation reaches a condition that would force a Boolean to become

indeterminate, the simulation is halted and an error is reported. Many Xilinx blocks have

control ports that only allow Boolean signals as inputs. The rule concerning indeterminate

Booleans means that such blocks never see an indeterminate on a control port

A UFix_1_0 is a type that is equivalent to Boolean except for the above restriction

concerning indeterminate data.

Block Masks and Parameter Passing

The same scoping and parameter passing rules that apply to ordinary Simulink blocks

apply to System Generator blocks. Consequently, blocks in the Xilinx Blockset can be

parameterized using MATLAB variables and expressions. This capability makes possible

highly parametric designs that take advantage of the expressive and computational power

of the MATLAB language.

Block Masks

In Simulink, blocks are parameterized through a mechanism called masking. In essence, a

block can be assigned mask variables whose values can be specified by a user through dialog

box prompts or can be calculated in mask initialization commands. Variables are stored in

a mask workspace. A mask workspace is local to the blocks under the mask and cannot be

accessed by external blocks.

Note:

It is possible for a mask to access global variables and variables in the base workspace. To

access a base workspace variable, use the MATLAB evalin function. For more information on the

MATLAB and Simulink scoping rules, refer to the manuals titled Using MATLAB and Using Simulink

from The MathWorks, Inc.

Parameter Passing

It is often desirable to pass variables to blocks inside a masked subsystem. Doing so allows

the block’s configuration to be determined by parameters on the enclosing subsystem. This

technique can be applied to parameters on blocks in the Xilinx blockset whose values are

set using a listbox, radio button, or checkbox. For example, when building a subsystem

that consists of a multiply and accumulate block, you can create a parameter on the

subsystem that allows you to specify whether to truncate or round the result. This

parameter will be called trunc_round as shown in the figure below.

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MATLAB DESIGN HDL CODER RELEASE NOTES User's Guide Page 37