Based on ARM Cortex-M3 microcontroller (STM32 series) basic knowledge (4) - ARM assembly language programming

Thumb pseudo-instruction

LDR (Large Range Address Read Pseudo-instruction)

ARM assembler structure

AREA: Used to define a code segment or data segment pseudo-operation.

CODE16: Used to tell the assembler that the instruction sequence that follows is a 16-bit Thumb instruction.

ARM or CODE32: Used to tell the assembler that the instruction sequence that follows is a 32-bit ARM instruction.

The GBLA pseudo-op is used to define a global numeric variable and initialize it to 0.

In an assembly language program, use the AREA pseudo-operation to define a segment, and describe the relevant attributes of the defined segment. This example defines aSnippet called Init，Property is read-only.The ENTRY pseudo-operation identifies the entry point of the program, followed by the instruction sequence, and the end of the program is the END pseudo-instruction, which tells the compiler the end of the source file. Each assembly program segment must have an END pseudo-operation to indicate the code segment. end of.

Notice

example

1. AREA (section definition directive)

example

2. CODE16、CODE32

3. ENTRY (program entry indication pseudo-instruction)

4. END (Program end pseudo-instruction)

5. EQU (equivalent pseudo-instruction)

6. EXPORT (global label declaration directive)

The EXPORT pseudo-operation is used to declare a global label in the program that can be referenced in other files. EXPORT can be replaced by GLOBAL. Labels are case-sensitive in the program.

7. IMPORT (label reference and add declaration directive)

8. Data Definition Pseudo-Operations (DCB, DCD, DCW)

assembly language programming

The steps to create an assembly language program are as follows:

example

C program to achieve the sum of 5 integers

Data block copy application example

 AREA reset,CODE,READONLY
num    EQU  20                         ;设置复制的字数
       ENTRY                           ;程序入口
start  LDR  r0,=src                    ;r0指向源数据块首地址
       LDR  r1,=dst                    ;r1指向目标数据块首地址
       MOV  r2,#num                    ;r2复制的字数
       MOV  sp,#0x400                  ;设置堆栈指针,用于保存工作寄存器数值
blockcopy
       MOVS r3,r2,LSR #3               ;需要进行的以8个字为单位的数据复制
       BEQ  copywords                  ;对剩余不足8个字数据,跳转到copywords
                                       ;以字为单位复制
       STMFD sp!,{
    
    r4-r11}              ;保存工作寄存器
octcopy
       LDMIA r0!,{
    
    r4-r11}               ;从数据源取出8个字数据放到寄存器,并更新R0
       STMIA r1!,{
    
    r4-r11}               ;将数据写入目的地址,并更新R1
       SUBS  r3,r3,#1                  ;将块复制次数减1
       BNE   octcopy                   ;循环直到完成以8个字为单位的复制

        LDMFD sp!,{
    
    r4-r11}              ;恢复工作寄存器
copywords
       ANDS r2,r2,#7                   ;剩余不足8个字的数据的字数
       BEQ  stop                       ;数据复制完成则跳转到stop  
wordcopy
       LDR  r3,[r0],#4                 ;从数据源取出一个字数据到R3,并更新R0
       STR  r3,[r1],#4                 ;将字数据存储到目标地址,并更新R1
       SUBS r2,r2,#1                   ;字复制次数减1
       BNE  wordcopy                   ;循环,直到字复制完毕
                                       ;定义数据区SRC和DST
stop 
       b stop                                      
       AREA reset,DATA,READWRITE
src    DCD 1,2,3,4,5,6,7,8,8,7,6,5,4,3,2,1
       dcb "abcd1234efgh5678"
dst    DCD 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       END

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