ARM DCD instruction-EEWORLD

Collect

The DCD (or DCDU)

syntax format is:

label DCD (or DCDU) expression.

The DCD (or DCDU) pseudo-instruction is used to allocate a continuous word storage unit and initialize it with the expression specified in the pseudo-instruction. The expression can be a program label or a numeric expression. DCD can also be replaced by "&".

The word storage unit allocated by DCD is word-aligned, while the word storage unit allocated by DCDU is not strictly word-aligned.

Usage example:

DataTest DCD 4, 5, 6; allocate a continuous word storage unit and initialize it.

In the interrupt vector table, do not directly LDR PC, "exception address". Instead, use a label, and then use DCD to define this label later. The reason is:

The LDR instruction can only jump to the current PC 4kB range, while the B instruction can jump to the 32MB range. Now, in the LDR PC, "xxxx" instruction, a word is defined with "xxxx" DCD, and this

The address of the final exception service program is stored in a word, so that a full-range jump of 4GB can be achieved.

In addition: there are the following statements

USR_STACK_LEGTH EQU 64 ; Define the user mode stack length to 64 words

StackUsr DCD UsrStackSpace + (USR_STACK_LEGTH-1)*4; define a word space, the content of this word is the first address of the descending stack

UsrStackSpace SPACE USR_STACK_LEGTH*4; Allocate a 64-word stack space for user mode. If this stack is used for decrement, its first address is

UsrStackSpace + (USR_STACK_LEGTH-1)*4

Keywords：ARM Reference address：ARM DCD instruction

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