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在下面的代码中
;- Load the stack base addresses
add r0, pc,#-(8+.-StackData) ; @ where to read values (relative)
1.不知道注释中的 @是干什么用的
2.不知道stack base addresses为什么要这么计算,而且这个表达式中有+.-,这是怎么一个算法呢?详细代码在下面.

3.BIC R0, R0, #%1011 ; 清除 R0 中的位 0、1、和 3。保持其余的不变。
其中,%是什么意思?这些规则我哪里能找到呢?这才是最重要的.谢谢大家

下面是一个AT91RM9200的START.S

;------------------------------------------------------------------------------
;- ATMEL Microcontroller Software Support - ROUSSET -
;------------------------------------------------------------------------------
; The software is delivered "AS IS" without warranty or condition of any
; kind, either express, implied or statutory. This includes without
; limitation any warranty or condition with respect to merchantability or
; fitness for any particular purpose, or against the infringements of
; intellectual property rights of others.
;-----------------------------------------------------------------------------
;- File source : cstartup_boot.arm
;- Object : Generic CStartup
;- Compilation flag : None
;-
;- 1.0 16/03/01 ODi, HI : Creation ARM ADS
;------------------------------------------------------------------------------
;--------------------------------
;- ARM Core Mode and Status Bits
;--------------------------------

ARM_MODE_USER EQU 0x10
ARM_MODE_FIQ EQU 0x11
ARM_MODE_IRQ EQU 0x12
ARM_MODE_SVC EQU 0x13
ARM_MODE_ABORT EQU 0x17
ARM_MODE_UNDEF EQU 0x1B
ARM_MODE_SYS EQU 0x1F

I_BIT EQU 0x80
F_BIT EQU 0x40
T_BIT EQU 0x20

;------------------------------------------------------------------------------
;- Stack Area Definition
;-----------------------
;-
;------------------------------------------------------------------------------
IRQ_STACK_SIZE EQU 0xFF
FIQ_STACK_SIZE EQU 0x04
ABT_STACK_SIZE EQU 0x04
UND_STACK_SIZE EQU 0x04
SVC_STACK_SIZE EQU 0x04
USER_STACK_SIZE EQU 0x4FF

AREA |C$$stack|, DATA

;- IRQ stack definition
AT91_IRQ_Stack_End DCD 0x55AA55AA
SPACE (IRQ_STACK_SIZE - 4)
AT91_IRQ_Stack_Begin EQU (AT91_IRQ_Stack_End + (IRQ_STACK_SIZE - 4))

;- FIQ stack definition
AT91_FIQ_Stack_End DCD 0x55AA55AA
SPACE (FIQ_STACK_SIZE - 4)
AT91_FIQ_Stack_Begin EQU (AT91_FIQ_Stack_End + (FIQ_STACK_SIZE - 4))

;- ABORT stack definition
AT91_ABT_Stack_End DCD 0x55AA55AA
SPACE (ABT_STACK_SIZE - 4)
AT91_ABT_Stack_Begin EQU (AT91_ABT_Stack_End + (ABT_STACK_SIZE - 4))

;- UNDEF stack definition
AT91_UND_Stack_End DCD 0x55AA55AA
SPACE (UND_STACK_SIZE - 4)
AT91_UND_Stack_Begin EQU (AT91_UND_Stack_End + (UND_STACK_SIZE - 4))

;- SVC stack definition
AT91_SVC_Stack_End DCD 0x55AA55AA
SPACE (SVC_STACK_SIZE-4)
AT91_SVC_Stack_Begin EQU (AT91_SVC_Stack_End + (SVC_STACK_SIZE-4))

;- USER and SYSTEM stack definition
AT91_USER_Stack_End DCD 0x55AA55AA
SPACE (USER_STACK_SIZE-4)
AT91_USER_Stack_Begin EQU (AT91_USER_Stack_End + (USER_STACK_SIZE-4))

EXPORT AT91_IRQ_Stack_End
EXPORT AT91_IRQ_Stack_Begin
EXPORT AT91_FIQ_Stack_End
EXPORT AT91_FIQ_Stack_Begin
EXPORT AT91_ABT_Stack_End
EXPORT AT91_ABT_Stack_Begin
EXPORT AT91_UND_Stack_End
EXPORT AT91_UND_Stack_Begin
EXPORT AT91_SVC_Stack_End
EXPORT AT91_SVC_Stack_Begin
EXPORT AT91_USER_Stack_End
EXPORT AT91_USER_Stack_Begin

;------------------------------------------------------------------------------
;- Area Definition
;-----------------
;- Must be defined as function to put first in the code as it must be mapped
;- at offset 0 of the flash EBI_CSR0, ie. at address 0 before remap.
;------------------------------------------------------------------------------
AREA reset, CODE, READONLY

; IMPORT __use_no_semihosting_swi
;------------------------------------------------------------------------------
;- Define the entry point
;------------------------

EXPORT __ENTRY
__ENTRY

;------------------------------------------------------------------------------
;- Exception vectors ( before Remap )
;------------------------------------
;- These vectors are read at address 0.
;- They absolutely requires to be in relative addresssing mode in order to
;- guarantee a valid jump. For the moment, all are just looping (what may be
;- dangerous in a final system). If an exception occurs before remap, this
;- would result in an infinite loop.
;------------------------------------------------------------------------------
B InitReset ; reset
undefvec
B undefvec ; Undefined Instruction
swivec
B swivec ; Software Interrupt
pabtvec
B pabtvec ; Prefetch Abort
dabtvec
B dabtvec ; Data Abort
rsvdvec
B rsvdvec ; reserved
irqvec
ldr pc, [pc,#-0xF20] ; IRQ : read the AIC
fiqvec
B fiqvec ; FIQ

;-------------------
;- The reset handler
;-------------------
InitReset

;------------------------------------------------------------------------------
;- Low level Init is performed in a C function: AT91F_LowLevelInit (APMC, AIC, EBI, ....)
;- Init Stack Pointer to a valid memory area before calling AT91F_LowLevelInit
;----------------------------------------------------------------------

IMPORT AT91F_LowLevelInit

ldr r1, = AT91_SVC_Stack_Begin
bic r1, r1, #3 ; Insure word alignement 位清除
mov sp, r1 ; Init stack SYS

ldr r0, = AT91F_LowLevelInit
mov lr, pc ;保存当前的程序指针
bx r0 ;跳到AT91F_LowLevelInit执行

;------------------------------------------------------------------------------
;- Setup the stack for each mode
;-------------------------
;- The processor will remain in the last initialized mode.
;------------------------------------------------------------------------------

;- Load the stack base addresses
add r0, pc,#-(8+.-StackData) ; @ where to read values (relative)
ldmia r0, {r1-r6}

;- Set up Supervisor Mode and set SVC Mode Stack
msr cpsr_c, #ARM_MODE_SVC:OR:I_BIT:OR:F_BIT ;传送一个寄存器的内容到状态标志
bic r1, r1, #3 ; Insure word alignement
mov sp, r1 ; Init stack SYS

;- Set up Interrupt Mode and set IRQ Mode Stack
msr CPSR_c, #ARM_MODE_IRQ:OR:I_BIT:OR:F_BIT
bic r2, r2, #3 ; Insure word alignement
mov sp, r2 ; Init stack IRQ

;- Set up Fast Interrupt Mode and set FIQ Mode Stack
msr CPSR_c, #ARM_MODE_FIQ:OR:I_BIT:OR:F_BIT
bic r3, r3, #3 ; Insure word alignement
mov sp, r3 ; Init stack FIQ

;- Set up Abort Mode and set Abort Mode Stack
msr CPSR_c, #ARM_MODE_ABORT:OR:I_BIT:OR:F_BIT
bic r4, r4, #3 ; Insure word alignement
mov sp, r4 ; Init stack Abort

;- Set up Undefined Instruction Mode and set Undef Mode Stack
msr CPSR_c, #ARM_MODE_UNDEF:OR:I_BIT:OR:F_BIT
bic r5, r5, #3 ; Insure word alignement
mov sp, r5 ; Init stack Undef

;- Set up user Mode and set Undef Mode Stack
msr CPSR_c, #ARM_MODE_SYS:OR:F_BIT
bic r6, r6, #3 ; Insure word alignement
mov sp, r6 ; Init stack Undef

b EndInitStack

StackData
DCD AT91_SVC_Stack_Begin
DCD AT91_IRQ_Stack_Begin
DCD AT91_FIQ_Stack_Begin
DCD AT91_ABT_Stack_Begin
DCD AT91_UND_Stack_Begin
DCD AT91_USER_Stack_Begin
EndInitStack

;------------------------------------------------------------------------------
;- Initialise C variables
;------------------------
;- Following labels are automatically generated by the linker.
;- R Read-only = the code
;- RW: Read Write = the data pre-initialized and zero-initialized.
;- ZI: Zero-Initialized.
;- Pre-initialization values are located after the code area in the image.
;- Zero-initialized datas are mapped after the pre-initialized.
;- Note on the Data position :
;- If using the ARMSDT, when no -rw-base option is used for the linker, the
;- data area is mapped after the code. You can map the data either in internal
;- SRAM ( -rw-base=0x40 or 0x34) or in external SRAM ( -rw-base=0x2000000 ).
;- Note also that to improve the code density, the pre_initialized data must
;- be limited to a minimum.
;------------------------------------------------------------------------------

add r2, pc,#-(8+.-CInitData) ; @ where to read values (relative)
ldmia r2, {r0, r1, r3, r4}

cmp r0, r1 ; Check that they are different
beq EndRW
LoopRW
cmp r1, r3 ; Copy init data
ldrcc r2, [r0], #4
strcc r2, [r1], #4
bcc LoopRW
EndRW

mov r2, #0
LoopZI
cmp r3, r4 ; Zero init
strcc r2, [r3], #4
bcc LoopZI

b EndInitC

CInitData
IMPORT |Image$$RO$$Limit| ; End of ROM code (=start of ROM data)
IMPORT |Image$$RW$$Base| ; Base of RAM to initialise
IMPORT |Image$$ZI$$Base| ; Base and limit of area
IMPORT |Image$$ZI$$Limit| ; Top of zero init segment

DCD |Image$$RO$$Limit| ; End of ROM code (=start of ROM data)
DCD |Image$$RW$$Base| ; Base of RAM to initialise
DCD |Image$$ZI$$Base| ; Base and limit of area
DCD |Image$$ZI$$Limit| ; Top of zero init segment
EndInitC

;------------------------------------------------------------------------------
;- Branch on C code Main function (with interworking)
;----------------------------------------------------
;- Branch must be performed by an interworking call as either an ARM or Thumb
;- main C function must be supported. This makes the code not position-
;- independant. A Branch with link would generate errors
;------------------------------------------------------------------------------
IMPORT main
_main
__main
EXPORT _main
EXPORT __main
ldr r0, =main
mov lr, pc
bx r0

;------------------------------------------------------------------------------
;- Loop for ever
;---------------
;- End of application. Normally, never occur.
;- Could jump on Software Reset ( B 0x0 ).
;------------------------------------------------------------------------------
End
b End



END