Load/Store Instructions
The ARM is a Load/Store Architecture: Does not support memory to memory data processing operations. Must move data values into registers before using them.ARM has three sets of instructions which
interact with main memory. These are
Single register data transfer(LDR/STR)
Block dtat transfer(LDM/STM)
Single Data Swap(SWP)
指令描述
LDR字资料载入指令
LDRB字节资料载入指令
LDRH半字资料载入指令
STR字资料存储指令
STRB字节资料存储指令
STRH半字资料存储指令
Syntax：
{}{} Rd,
Load and Store
word or Byte，offset from the base register
指令说明
LDR R0,[R1]将地址R1处字资料读入R0
LDR R0, [R1, R2]将地址R1+R2处字资料读入R0
LDR R0,[R1, #8]将地址R1+8处字资料读入R0
LDR R0, [R1, R2]!将地址R1+R2处字资料读入R0,并将新地址R1+R2写入R1
LDR R0, [R1, #8]!将地址R1+8处字资料读入R0,并将新地址R1+8写入R1
LDR R0, [R1], R2将地址R1的字资料读入R0,并将新地址R1+R2写入R1
LDR R0, [R1, R2,LSL #2]!将地址R1+R2x4处字资料读入R0,新址R1+R2x4写入R1
LDR R0,[R1],R2,LSL #2将地址R1处字资料写入R0,新址R1+R2x4写入R1
STR r0,[r1,#-12]将r0写入到地址r1-12处
Example：Write a segment of code that add together elements x to x+(n-1) of an array, where the element x = 0 is the first element of the array. Each element of the array is
word size(ie, 32bits). The segment should use post-indexed addressing.At the start of your segments, you should assume that: r0 points to the start of the array, r1 = x, r2 = n;
Sample Solution:
DataSpace SPACE 100; 连续分配100个字节的存储单元并初始化为0
ADD r0, r0, r1, LSL#2
ADD r2, r0, r2, LSL#2
MOV r1, #0
loop
LDR r3, [r0],#4
ADD r1, r1, r3
CMP r0, r3
BLT loop
Block Data Transfer
The Load and Store Multiple instruction(LDM/STM) allow between 1 and 16 registers to be transferred to or from memory.
格式：
LDM(STM){条件}{类型}基址寄存器{!}，寄存器列表{^}
该指令常见用途是将多个寄存器的内容入栈或出栈。类型包括非堆栈型寻址或堆栈型寻址。
寻址说明
IA Increment After基址寄存器在取后才增加
IB Increment Before基址寄存器在取前才增加
DA Decrement After基址寄存器在存取后才减少
DB Decrement Before基址寄存器在存取前即减少
FD Full Descending满递减
FA Full Ascending满递增
ED Empty Descending空递减
EA Empty Ascending空递增
Traditionaly, a stack grows down in memory, with the last ‘pushed’ value at the lowest address. The ARM also supports ascending stacks, where the stack structure grows up through memory. The value of the stack pointer can either:
Point to the last occupied address(Full stack)―and so needs pre-decrementing(ie before the push). Point to the next occupied address(Empty stack)―and so needs post-decrementing(ie after the push)
注意，象STMFD, STMED，STMFA和STMEA分别跟LDMFD, LDMED, LDMFA和LDMEA配对，故理解不能全部按照字面意思来。
资料交换指令
语法
SWP{}{B} Rd, Rm, [Rn]
SWP{条件}{B} 目的寄存器，来源寄存器1，[来源寄存器2]
