One of the ARM assembly control pseudo instructions-EEWORLD

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    Assembly control pseudo instructions are used to control the execution flow of the assembly program. Commonly used assembly control pseudo instructions include the following:
    — IF, ELSE, ENDIF
    — WHILE, WEND
    — MACRO, MEND
    — MEXIT

1. IF, ELSE, ENDIF

Syntax format:

IF logical expression

Instruction sequence 1

ELSE

Instruction sequence 2

ENDIF

The IF, ELSE, and ENDIF pseudo-instructions can determine whether to execute a certain instruction sequence based on whether a condition is met.

If the expression is true, execute instruction sequence 1, otherwise execute instruction sequence 2. Among them, ELSE and instruction sequence 2 can be absent. In this case, when

If the logical expression following IF is true, instruction sequence 1 is executed, otherwise the following instructions are continued to be executed.

IF, ELSE, and ENDIF directives can be nested.

Example of use:

GBLL Test; declare a global logic variable named Test...

IF Test = TRUE

Instruction sequence 1

ELSE

Instruction sequence 2

ENDIF

2. WHILE, WEND

Syntax format:

WHILE logical expression

Instruction sequence

WEND

The WHILE and WEND pseudo-instructions can determine whether to loop and execute a certain instruction sequence based on whether a condition is met.

If the expression is true, the instruction sequence is executed. After the instruction sequence is executed, the value of the logical expression is judged. If it is true, the execution continues.

The logical expression evaluates to false.

WHILE and WEND directives can be nested.

Example of use:

GBLA Counter; declare a global math variable named Counter

Counter SETA 3; The number of loops is controlled by the variable Counter

…

WHILE Counter < 10

Instruction sequence

WEND

3. MACRO, MEND

Syntax format:

$label macro name$parameter 1, $parameter 2, ...

Instruction sequence

MEND

MACRO and MEND pseudo instructions can define a section of code as a whole, called a macro instruction, and then you can use macro instructions in the program.

Call this code multiple times. The $ symbol will be replaced by a user-defined symbol when the macro is expanded. The macro can be used

One or more parameters that are replaced by their values when the macro is expanded.

The usage and function of macro instructions are similar to those of subroutines. Subroutines can provide modular programming, save storage space and improve

However, when using the subroutine structure, the scene needs to be protected, which increases the system overhead. Therefore, when the code is short and needs to be passed

When there are many parameters, macro instructions can be used instead of subroutines.

The instruction sequence between MACRO and MEND is called the macro definition body. The first line of the macro definition body should declare the prototype of the macro (including the macro

The instruction sequence can then be called in the assembler by the macro name. When the source program is compiled, the assembler will

Call expansion replaces the macro call in the program with the instruction sequence in the macro definition and passes the value of the actual parameter to the formal parameter in the macro definition.

MACRO and MEND directives can be nested.

4. MEXIT

Syntax format:

MEXIT

MEXIT is used to jump out of a macro definition.

Keywords：ARM Reference address：One of the ARM assembly control pseudo instructions

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