Altera Nios II Custom Uživatelský manuál stáhnout pdf (Strana 18)

2–2 Chapter 2: Software Interface

Built-in Functions and User-defined Macros

Nios II Custom Instruction User Guide January 2011 Altera Corporation

Example 2–2 illustrates how most applications use custom instructions. The macros

defined by the Nios II software build tools use C integer types only. Occasionally,

applications require input types other than integers. In those cases, you can use a

custom instruction macro to process non-integer return values.

1 You can define custom macros for Nios II custom instructions that allow other 32-bit

input types to interface with custom instructions.

Built-in Functions and User-defined Macros

The Nios II processor uses gcc built-in functions to map to custom instructions. By

default, the integer type custom instruction is defined in a system.h file. However, by

using built-in functions, software can use non-integer types with custom instructions.

Fifty-two built-in functions are available to accommodate the different combinations

of supported types.

Built-in function names have the following format:

__builtin_custom_

Table 2–1 lists the 32-bit types supported by custom instructions as parameters and

return types, as well as the abbreviations used in the built-in function names.

Example 2–3 shows the prototype definitions for two built-in functions.

The built-in function

__builtin_custom_nf

takes a

float

as an input, and does not

return a value. In contrast, the built-in function

__builtin_custom_fnp

takes a pointer

as input, and returns a

float

To support non-integer input types, define macros with mnemonic names that map to

the specific built-in function required for the application.

f Refer to Appendix B, Custom Instruction Built-in Functions for detailed information

and a list of built-in functions.

Table 2–1. 32-bit Types Supported by Custom Instructions

32-bit Type Built-in Function Abbreviation

int i

float f

void * p

Example 2–3. Two Example Built-in Function Prototypes

void __builtin_custom_nf (int n, float dataa);

float __builtin_custom_fnp (int n, void * dataa);

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Altera Nios II Custom Uživatelský manuál Strana 18