National Instruments AutoCode NI MATRIX - Manual (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