National-instruments AutoCode NI MATRIX Manuel d'utilisateur télécharger pdf (Page 43)

Chapter 2 C Language Reference

AutoCode Reference 2-26 ni.com

data-typed variables reflecting each subsystem input signal and type.

The outputs to the subsystem are provided by the argument

Y, a pointer

to a structure named

_Subsys_

number

_out. This structure has mixed

data-typed variables reflecting each subsystem output signal and type.

The following overall steps need to be taken to invoke the subsystem

function:

1. Create an object of type

_Subsys_1_in (see generated subsystem

code) and copy in the inputs to the subsystem. A pointer to this object

will be passed as argument

U to the subsystem.

2. Create an object of type

_Subsys_1_out where the outputs of the

subsystem will be stored. A pointer to this object will be passed as

argument

Y to the subsystem.

3. Invoke the procedure using pointers to the objects created in steps 1

and 2.

C Fixed-Point Arithmetic

Fixed-point calculations provide significant advantages over floating-point

arithmetic. These include:

• Faster execution on most processors

• 8-bit, 16-bit, and 32-bit representations of fixed-point numbers

• Ability to interface to inexpensive processors that do not support

floating-point arithmetic

This section describes the implementation of fixed-point arithmetic in

AutoCode/C.

Note The SystemBuild User Guide has a fixed-point arithmetic chapter that explains the

basics of fixed-point arithmetic and the use of fixed-point arithmetic in SystemBuild

models.

Fixed-Point AutoCode/C Implementation

SystemBuild lets you represent vectors as fixed-point signals to which

fixed-point arithmetic will be applied. Refer to the SystemBuild User

Guide. Fixed-point signals and numbers are represented in AutoCode/C

as integer data types. An associated radix position—that is, the integer

marking the point that divides the integer and fractional part of the

1 2 ... 38 39 40 41 42 43 44 45 46 47 48 ... 249 250

Pas de commentaire

National-instruments AutoCode NI MATRIX Manuel d'utilisateur Page 43