TQ2440启动代码分析（二）
;;;;;;;;;;;;; When EINT0 is pressed, Clear SDRAM
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; check if EIN0 button is pressed
；这一段检测EINT0是否被按下，假如EINT0被按下，则清空SDRAM
ldr r0,=GPFCON
ldr r1,=0x0
str r1,[r0]
ldr r0,=GPFUP
ldr r1,=0xff
str r1,[r0]
;配置GPF
ldr r1,=GPFDAT
ldr r0,[r1]
bic r0,r0,#(0x1e<<1) ; bit clear
tst r0,#0x1
bne %F1
; Clear SDRAM Start
ldr r0,=GPFCON
ldr r1,=0x55aa
str r1,[r0]
; ldr r0,=GPFUP
; ldr r1,=0xff
; str r1,[r0]
ldr r0,=GPFDAT
ldr r1,=0x0
str r1,[r0] ;LED=****
mov r1,#0
mov r2,#0
mov r3,#0
mov r4,#0
mov r5,#0
mov r6,#0
mov r7,#0
mov r8,#0
ldr r9,=0x4000000 ;64MB
ldr r0,=0x30000000
0
stmia r0!,{r1-r8}
subs r9,r9,#32
bne %B0
;以上这段清空SDRAM
;Clear SDRAM End
1
;Initialize stacks
bl InitStacks
;检测引脚OM[1:0]，如果OM[1:0]!=0,选择从NOR Flash启动，如果OM[1:0]==0，则表示从nand flash启动
;===========================================================
ldr r0, =BWSCON
ldr r0, [r0]
ands r0, r0, #6 ;OM[1:0] != 0, NOR FLash boot
bne copy_proc_beg ;do not read nand flash
adr r0, ResetEntry ;OM[1:0] == 0, NAND FLash boot
cmp r0, #0 ;if use Multi-ice,
bne copy_proc_beg ;do not read nand flash for boot
;nop
;===========================================================
nand_boot_beg
[ {TRUE}
bl RdNF2SDRAM
]
;nand flash启动，拷贝程序到steppingstone区域
ldr pc, =copy_proc_beg
;===========================================================
copy_proc_beg;
adr r0, ResetEntry
ldr r2, BaseOfROM
cmp r0, r2
ldreq r0, TopOfROM
beq InitRam
ldr r3, TopOfROM
0
ldmia r0!, {r4-r7}
stmia r2!, {r4-r7}
cmp r2, r3
bcc %B0
sub r2, r2, r3
sub r0, r0, r2
InitRam
ldr r2, BaseOfBSS
ldr r3, BaseOfZero
0
cmp r2, r3
ldrcc r1, [r0], #4
strcc r1, [r2], #4
bcc %B0
mov r0, #0
ldr r3, EndOfBSS
1
cmp r2, r3
strcc r0, [r2], #4
bcc %B1
ldr pc, =%F2 ;goto compiler address
2
; [ CLKDIV_VAL>1 ; means Fclk:Hclk is not 1:1.
; bl MMU_SetAsyncBusMode
; |
; bl MMU_SetFastBusMode ; default value.
; ]
;===========================================================
; Setup IRQ handler
ldr r0,=HandleIRQ ;This routine is needed
ldr r1,=IsrIRQ ;if there is not subs pc,lr,#4 at 0x18, 0x1c
str r1,[r0]
[ :LNOT:THUMBCODE
bl Main ;Do not use main() because ......
b .
]
[ THUMBCODE ;for start-up code for Thumb mode
orr lr,pc,#1
bx lr
CODE16
bl Main ;Do not use main() because ......
b .
CODE32
]
;堆栈初始化的顺序决定系统最后运行在哪种处理器模式，最后初始化哪种模式的堆栈，系
;统就运行在哪种模式。
;function initializing stacks
InitStacks
;Do not use DRAM,such as stmfd,ldmfd......
;SVCstack is initialized before
;Under toolkit ver 2.5, msr cpsr,r1 can be used instead of msr cpsr_cxsf,r1
mrs r0,cpsr
bic r0,r0,#MODEMASK
orr r1,r0,#UNDEFMODE|NOINT
msr cpsr_cxsf,r1 ;UndefMode
ldr sp,=UndefStack ; UndefStack=0x33FF_5C00
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