Summary of common instructions for arm assembly

ARM A summary of common assembly instructions

1.EQU

assignment

; take 0x40013800  Assign a value to a variable USART1_BASE( Register address )
USART1_BASE         EQU    0x40013800 

2.AREA

usage ：AREA sectionname{,attr}{,attr}…

sectionname： The segment name to be specified

attr： Segment properties

Attribute enumeration

ALIGN=expression

By default ,ELF Segments are aligned on four byte boundaries .expression You can have 0 To 31 Any integer of . Paragraph in 2expression Align on byte boundaries . for example , If expression yes 10, Then the paragraph is in 1KB Align on boundary . This is related to ALIGN The command is not specified in the same way .

ASSOC=section

section Specify an associated ELF paragraph .sectionname Must be included in the section In any link to .

CODE

Contains machine instructions .READONLY Is the default value .

COMDEF

Is a common segment definition . This is what contains code or data ELF paragraph . It must be the same as any other segment with the same name in other source files . The same... With the same name ELF Segments are overwritten by linked programs in the same segment of memory . If any paragraph is different , The linker generates a warning , And do not cover these segments . see also RealView Compiler tools 2.0 Version of the linker and utility guide Linker in chapter .

COMMON

Is a public data segment . No code or data can be defined in it . The reason is
Linker initialized to zero . All public segments with the same name exist
The same segment of the memory is overwritten by the linked program . They don't all need to have
The same size . Linker according to the needs of the largest common segment of each name
Allocate space .

DATA

Contains data but no instructions .READWRITE Is the default value .

NOALLOC

Indicates that this... Is not available on the target system AREA Allocate memory .

NOINIT

Indicates that the data segment is uninitialized or initialized to zero . It contains only zero initialized space reservation commands SPACE or DCB、DCD、DCDU、DCQ、DCQU、DCW or DCWU. You can decide when linking AREA Is it uninitialized or zero initialized （ see also RealView Compiler tools 2.0 Version of the linker and utility guide Linker in chapter ）.

READONLY

Indicates that it cannot be written to this segment . This is the default for code regions .

READWRITE

It means you can read and write this paragraph . This is the default for data areas

3.DCD

Allocate storage units for specific data , At the same time, it can complete the initialization of the allocated storage unit .

    AREA RESET, DATA, READONLY 
    DCD    MSP_TOP            ; Initialize main stack  
    DCD    Start              ; Reset vector  
    DCD    NMI_Handler        ;NMI Handler 
    DCD    HardFault_Handler  ;Hard Fault Handler 
    DCD    0                   
    DCD    0 
    DCD    0 
    DCD    0 
    DCD    0 
    DCD    0 
    DCD    0 
    DCD    0 
    DCD    0 
    DCD    0 
    DCD    0 
    DCD    SysTick_Handler    ;SysTick Handler 
    SPACE  20                 ; Reserve space 20 byte 

4. ENTRY

Develop entry points for assemblers , There must be at least one in a complete assembler ENTRY（ There can be more than one , When there is more than one ENTRY when , The real entry point of the program is specified by the linker ）, But there can be at most one in a source file ENTRY（ There can be no ）.

    AREA |.text|, CODE, READONLY 
    ; The main program starts  
    ENTRY                            
    ; Instructs the program to execute from here  

5. START

A label , Mark the entry of the program , After the program is loaded into memory CS,IP Will point to this label , from START The instruction pointed to starts running .

Finally, we should cooperate END Use

6. LDR

Format ：LDR{ Conditions } Destination register < Memory address >

1、 ldr pc, =label

Namely the label Of data or instructions after Running address The assignment is pc. Running address = Link address + The offset of these data or instructions from the program start address .

2、 ldr pc, label

hold label Data or instructions after Content Assign a value to pc.

    ldr    r0, =RCC_CR 
    ldr    r1, [r0] 

7. STR

General follow LDR In combination with . usage ：STR r1,[r2] ; take r1 Save the value in to r2 In the specified address

    ldr    r0, =RCC_CR 
    ldr    r1, [r0] 
    orr    r1, #Bit16 
    str    r1, [r0] 

8.BEQ

CPSR Of Z The identification bit is 1 when , The program jumps to beq At the label after

; Wait for the external crystal oscillator to be ready 
ClkOk           
    ldr    r1, [r0] 
    ands   r1, #Bit17 
    beq    ClkOk 
    

9.MSR/MRS

MRS, The status register is transferred to the general register class instruction , Transfer the contents of the status register to the general purpose register .

Format ：MRS{< Condition code >}Rd,CPSR}SPSR

MSR, General register transfer to status register transfer instruction , Transfer the contents of the general register to the status register .

Format ：MSR{< Condition code >CPSR_f|SPSR_f,<#immed_8r>

    ; Switch to user level line program mode  
    ldr    r0, =PSP_TOP                   
    ; Initialize thread stack  
    msr    psp, r0 
    mov    r0, #3 
    msr    control, r0 

10.B/BL/BX

All three are program jumps , but B Is pure jump , Will not return ,BL After the jump is executed, it will return to the original position , Used to execute subroutines .BX The instruction at the destination address of the jump can be either ARM Instructions , It can also be Thumb Instructions .

The format is ：B/BL/BX Destination address

bx lr; Represents the return of a subroutine 

11.PUSH/POP

Press data into / Pop up stack

; Is equivalent to r0,r1, r2, r3 Registers are passed as parameters into the subroutine stack 
push   {r0 - r3} 
...
; Clear subroutine stack 
pop    {r0 - r3} 

Logical operators

ARM assembly ： Data processing instruction set