Zilog ZUSBOPTS Manual de usuario descargar pdf (Pagina 193)

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101

UM017105-0511 Language Extensions

Zilog Developer Studio II – ZNEO™

User Manual

165

Placement of Consecutive Variables

The compiler also provides syntax to place several variables at consecutive addresses.

For example:

char ch1 _At 0xbef0;

char ch2 _At …;

char ch3 _At …;

This example places ch1 at address 0xbef0, ch2 at the next address (0xbef1) after ch1,

and

ch3 at the next address (0xbef2) after ch2. The _At … directive can only be used

after a previous

_At or _Align directive.

Alignment of a Variable

The following syntax can be used to declare a global or static variable aligned at a speci-

fied alignment:

char ch2 _Align 2; // ch2 is aligned at even boundary

char ch4 _Align 4; // ch4 is aligned at a four byte boundary

Only aligned variables with the rom or erom storage class specifiers can be initialized. The

aligned variables with the

near and far storage class specifiers cannot be initialized. The

uninitialized aligned variables are not initialized to zero by the compiler startup routine.

String Placement

When string constants (literals) such as "mystring" are used in a C program, they are

stored by the C-Compiler in RAM address space for the small memory model and in

ERAM address space for the large memory model. However, sometimes this default

placement of string constants does not allow you adequate control over your memory

usage. Therefore, language extensions are provided to give you more control over string

placement:

N"mystring". This constant defines a near string. The string is stored in RAM. The

address of the string is a _Near pointer.

F"mystring". This constant defines a far string. The string is stored in ERAM. The

address of the string is a _Far pointer.

R"mystring". This constant defines a ROM string. The string is stored in ROM. The

address of the string is a _Rom pointer.

Note:

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