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最新推荐文章于 2024-04-12 14:55:31 发布

Lu_ming

最新推荐文章于 2024-04-12 14:55:31 发布

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文章标签： structure float string byte

本文链接：https://blog.youkuaiyun.com/Lu_ming/article/details/1690243

本文详细介绍了ARM汇编语言中用于分配和初始化内存单元的各种伪指令，包括DCB、DCW、DCD等，并解释了如何使用这些指令来指定不同类型的数据。此外，还介绍了如何定义宏及一些有用的运算符。

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In ARM pseudo-instruction, some can be used to allocalte and initialize a block of memory units.

DCB - to allocate a block of "byte" type memory units and to initialize them by specified data.
DCB is also replaced by "=".

DCW{U} - to allocate a block of "half-word"(two bytes) type memory units and to initialize them by specified data.
if with "U", those allocated memory units is not aligned.

DCD{U} - to allocate a block of "word"(four bytes) type memory units and to initialize them by specified data.
if with "U", those allocated memory units is not aligned. DCD is also replaced by "&".

DCFD{U} - to allocate a block of "double float" type memory units and to initialize them by specified data.
if with "U", those allocated memory units is not aligned.

DCFS{U} - to allocate a block of "single float" type memory units and to initialize them by specified data.
if with "U", those allocated memory units is not aligned.

DCQ{U} - to allocate a block of "8 bytes" type memory units and to initialize them by specified data.
if with "U", those allocated memory units is not aligned.

SPACE - to allocate a block of sequential memory units an to initialize with 0.

Format: Label SPACE expression

DataSpace SPACE 100

MAP and FIELD
MAP/^ expression{, base_register}
The MAP is used to define a start address of a structure memory table. If the "base_register" is ignored,
the value of "expression" is considered as the start address of a structure; otherwise, the start address of
a structure is the sum of the value of "expression" and the value of "base_register".

MAP 0x100, R0

Label FIELD/# expression
The FIELD is used to define a data field in a structure. The value of "expression" tell how many bytes
is occupied. It usually is used with MAP.

Notice: The above twp pesudo-instruction just declare a structure and do not allocate memory.

MAP 0x100
A   FIELD 16 ; at 0x100
B   FIELD 32 ; at 0x110
S   FIELD 256 ; at 0x130

How to define a macro?

$Label Macro_name $arg1, $arg2, ...
codes...
MEND

There is a MEXIT can escape out from a macro body.

There are some useful operators.

?X
The "?" can return the length of the executable from the expression "X".

: DEF: X
To test whether a symbol "X" is defined.

: STR: X
To convert a number expression or boolean expression into a string. For number, the
"STR" just convert it to a hexadecimal numeric string; for boolean expression, convert
it to "T" or "F" string.

X: LEFT: Y / X: RIGHT: Y
To get a sub-string from the left or the right of "X", "Y" specify the number of
characters.

X: CC: Y
To append "Y" into "X".