Zilog ZUSBOPTS Manual do Utilizador descarregar pdf (Página 195)

100

101

UM017105-0511 Language Extensions

Zilog Developer Studio II – ZNEO™

User Manual

167

Inline Assembly Using the Pragma Directive

The first method uses the #pragma feature of ANSI C with the following syntax:

#pragma asm “<assembly line>”

#pragma can be inserted anywhere within the C source file. The contents of

<assembly line> must be legal assembly language syntax. The usual C escape sequences

(such as

\n, \t, and \r) are properly translated. Currently, the compiler does not process

the <assembly line>. Except for escape sequences, it is passed through the compiler verba-

tim.

Inline Assembly Using the asm Statement

The second method of inserting assembly language uses the asm statement:

asm(“<assembly line>”);

The asm statement cannot be within an expression and can be used only within the body of

a function.

The <assembly line> can be any string.The compiler does not check the legality of the

string.

As with the

#pragma asm form, the compiler does not process the <assembly line>

except for translating the standard C escape sequences.

The compiler prefixes the name of every global variable name with "_". Global variables

can therefore be accessed in inline assembly by prefixing their name with "_ ". The local

variables and parameters cannot be accessed in inline assembly.

Char and Short Enumerations

The enumeration data type is defined as int as per ANSI C. The C-Compiler provides

language extensions to specify the enumeration data type to be other than

int to save

space. The following syntax is provided by the C-Compiler to declare them as

char or

short:

enum

{

RED = 0,

YELLOW,

BLUE,

INVALID

} char color;

enum

{

NEW= 0,

OPEN,

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