AN3350 datasheet(62/185 Pages) STMICROELECTRONICS

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Working with the assembler

AN3350

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Doc ID 018512 Rev 2

other files to use the symbol, you must use the .extern symbol directive to declare the

symbol as external.

10.3.9

Weak symbols

Weak symbols, defined using the .weak symbol directive, are treated as global by the

assembler, however the linker handles them differently. When the linker resolves an external

symbol, the linker attempts to use the (single) global definition for that symbol. If no such

definition exists, the linker uses the first corresponding weak symbol definition it encounters

in one of the linked files.

10.3.10

Scope rules

All .global declarations take precedence over .weak declarations. Both .global and

.weak

declarations take precedence over .extern declarations. To avoid link errors, you

must declare symbols used and not defined in a file as external.

Note:

The assembler must be able to fully resolve symbols before you can use them in the

definition of an .equ symbol, value directive or symbols influencing the address

location of the generated code (see Section 10.4.2: Data storage).

10.3.11

Strings

A string is a sequence of characters enclosed in double quotes (“). Characters preceded by

the backslash character (\) have special meaning, as shown in Table 5.

10.4

Instructions and directives

The assembler does not translate directives directly into machine-language instructions.

Instead, directives allow you to control issues such as memory layout (addresses for storing

data, data contents, data alignment), symbol manipulation, structural grouping of

statements, and so on.

Table 5.

Special characters in strings

Special characters

Expands to

backspace

new line

return

tab

\”

double quote

backslash

\xnn

hexadecimal equivalent — For example, \x6B expands to the letter

Note: Hexadecimal strings required by the .hexa directive do not

require the \x prefix. Instead, the .hexa string is a sequence

of two-digit hexadecimal values, each digit represented by one

ASCII character. For example, .hexa “4869” stores two

bytes: 72, and 105.

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