Windows CE 休眠唤醒全面解析(基于2440平台)(3)
那么当CPU 唤醒之后，它运行的第一段程序是什么呢？这点很重要，因为唤醒=Power Reset，那么Reset CPU之后，运行第一段程序自然就是Bootloader了，那么我们看看，Bootloader里是怎么处理的。
这里我以常用的三星提供的Nboot为例。Bootloader的入口点是
ENTRY
;1)The code, which converts to Big-endian, should be in little endian code.
;2)The following little endian code will be compiled in Big-Endian mode.
; The code byte order should be changed as the memory bus width.
;3)The pseudo instruction,DCD can't be used here because the linker generates error.
ASSERT :DEF:ENDIAN_CHANGE
b ResetHandler ; 0x00 Reset
b . ; 0x04 Undefined
b . ; 0x08 Supervisor
b . ; 0x0c Prefetch Abort
b . ; 0x10 Data Abort
b . ; 0x14 Reserved
b . ; 0x18 IRQ
b . ; 0x1c FIQ
在这里，如果是Reset复位，那么就会跳转到0地址，也就是ResetHandler 去执行。
ResetHandler
ldr r0, = GPFCON
ldr r1, = 0x55aa
str r1, [r0]
ldr r0,=WTCON ;watch dog disable
ldr r1,=0x0
str r1,[r0]
ldr r0,=INTMSK
ldr r1,=0xffffffff ;all interrupt disable
str r1,[r0]
ldr r0,=INTSUBMSK
ldr r1,=0x7ff ;all sub interrupt disable
str r1,[r0]
ldr r0, = INTMOD
mov r1, #0x0 ; set all interrupt as IRQ (not FIQ)
str r1, [r0]
; configure GPIO pins
bl Port_Init
; CLKDIVN
ldr r0,=CLKDIVN
ldr r1,=0x7 ; 0x0 = 1:1:1 , 0x1 = 1:1:2 , 0x2 = 1:2:2 , 0x3 = 1:2:4, 0x4 = 1:4:4, 0x5 = 1:4:8, 0x6 = 1:3:3, 0x7 = 1:3:6
str r1,[r0]
; delay
mov r0, #DELAY
5 subs r0, r0, #1
bne %B5
; MMU_SetAsyncBusMode FCLK:HCLK= 1:2
ands r1, r1, #0x2
beq %F1
mrc p15,0,r0,c1,c0,0
orr r0,r0,#R1_nF:OR:R1_iA
mcr p15,0,r0,c1,c0,0
1
;To reduce PLL lock time, adjust the LOCKTIME register.
ldr r0,=LOCKTIME
ldr r1,=0xffffff
str r1,[r0]
; delay
mov r0, #DELAY
5 subs r0, r0, #1
bne %B5
;Configure MPLL
ldr r0,=MPLLCON
ldr r1,=((110<<12)+(3<<4)+1) ;Fin=16MHz,Fout=399MHz
; ldr r1,=((0xf6<<12)+(0xd<<4)+0x0) ;Fin=12MHz,Fout=200MHz
str r1,[r0]
; delay
mov r0, #DELAY
5 subs r0, r0, #1
bne %B5
;Configure UPLL
ldr r0, =UPLLCON
ldr r1, =((60<<12)+(4<<4)+2) ;Fin=16MHz, Fout=48MHz
; ldr r1, =((0x48<<12)+(0x3<<4)+0x2) ;Fin=12MHz, Fout=48MHz
str r1, [r0]
; delay
mov r0, #0x200
5 subs r0, r0, #1
bne %B5
以上部分无论是HardReset还是PowerReset都要执行，主要是做的初始化CPU时钟的工作，接下来
; :::::::::::::::::::::::::::::::::::::::::::::
; BEGIN: Power Management
; - - - - - - - - - - - - - - - - - - - - - - -
ldr r1, =GSTATUS2 ; Determine Booting Mode
ldr r10, [r1]
tst r10, #0x2
beq %F2 ; if not wakeup from PowerOffmode Skip
; MISCCR setting
LED_ON 0xc
str r10, [r1] ; Clear Test
; B .
ldr r1, =MISCCR ; MISCCR's Bit 17, 18, 19 -> 0
ldr r0, [r1] ; I don't know why, Just fallow Sample Code.
bic r0, r0, #(3 << 17) ; SCLK0:0->SCLK, SCLK1:0->SCLK, SCKE:L->H
str r0, [r1]
; Set memory control registers
add r0, pc, #SMRDATA - (. + 8)
ldr r1, =BWSCON ; BWSCON Address
add r2, r0, #52 ; End address of SMRDATA
loop10
ldr r3, [r0], #4
str r3, [r1], #4
cmp r2, r0
bne loop10
mov r1, #256
loop11
subs r1, r1, #1 ; wait until the SelfRefresh is released.
bne loop11
ldr r2, =0x201000 ; offset into the RAM
add r2, r2, #0x30000000 ; add physical base
mov pc, r2 ; & jump to StartUp address
nop
nop
nop
b .
b %F3 ; if wakeup from PowerOff mode
; goto Power-up code.
; Watchdog reset
2
tst r10, #0x4 ; In case of the wake-up from Watchdog reset,
; go to SDRAM start address(0x3000_0000)
b %F4 ; If not wakeup from Watchdog reset,
; beq %F4 ; If not wakeup from Watchdog reset,
; goto Normal Mode.
mov r0, #4
str r0, [r1] ; Clear the GSTATUS2. Because same code is located in memory address.
; Set memory control registers
ldr r0, =SMRDATA
ldr r1, =BWSCON ; BWSCON Address
add r2, r0, #52 ; End address of SMRDATA
loop0
ldr r3, [r0], #4
str r3, [r1], #4
cmp r2, r0
bne loop0
mov r1, #256
loop1
subs r1, r1, #1 ; wait until the SelfRefresh is released.
bne loop1
ldr r2, =0x201000 ; offset into the RAM
add r2, r2, #0x30000000 ; add physical base
mov pc, r2 ; & jump to StartUp address
b .
; Case of Power off reset
3
ldr r1, =MISCCR ; MISCCR's Bit 17, 18, 19 -> 0
ldr r0, [r1] ; I don't know why, Just fallow Sample Code.
bic r0, r0, #(3 << 17) ; SCLK0:0->SCLK, SCLK1:0->SCLK, SCKE:L->H
str r0, [r1]
; - - - - - - - - - - - - - - - - - - - - - - -
; END: Power Management
; :::::::::::::::::::::::::::::::::::::::::::::
4
; Configure memory controller
;ldr r0,=SMRDATA
add r0, pc, #SMRDATA - (. + 8)
ldr r1,=BWSCON ;BWSCON Address
add r2, r0, #52 ;End address of SMRDATA
0
ldr r3, [r0], #4
str r3, [r1], #4
cmp r2, r0
bne %B0
BringUpWinCE
……..
……..
……..
…….
这段代码，首先通过读取 GSTATUS2 寄存器里的数值，来判断Reset的原因，我们之前提到过，如果这个值是0x2,那么就是唤醒引起的PowerReset.
ldr r1, =GSTATUS2 ; Determine Booting Mode
ldr r10, [r1]
tst r10, #0x2
beq %F2 ; if not wakeup from PowerOffmode Skip
; MISCCR setting
判断GSTATUS2 里的数值是否为0x2,如果是的话，继续向下执行唤醒的恢复操作，否则就跳转到标签为2的程序段去执行。
标签2的程序中，判断GSTATUS2里的数值是否为0x4,如果是的话，说明发生了看门狗reset,那么要执行看门狗reset的恢复过程。
如果二者都不是的话，那么就认为是发生了Hard Reset,那么就按照正常的步骤，去加载Wince系统。
好，我们接着看看，假如GSTATUS2里的数值为2的话。那么就不会跳转到标签2的程序段中，而是向下执行这段程序。
LED_ON 0xc
str r10, [r1] ; Clear Test
; B .
ldr r1, =MISCCR ; MISCCR's Bit 17, 18, 19 -> 0
ldr r0, [r1] ; I don't know why, Just fallow Sample Code.
bic r0, r0, #(3 << 17) ; SCLK0:0->SCLK, SCLK1:0->SCLK, SCKE:L->H
str r0, [r1]
; Set memory control registers
add r0, pc, #SMRDATA - (. + 8)
ldr r1, =BWSCON ; BWSCON Address
add r2, r0, #52 ; End address of SMRDATA
loop10
ldr r3, [r0], #4
str r3, [r1], #4
cmp r2, r0
bne loop10
mov r1, #256
loop11
subs r1, r1, #1 ; wait until the SelfRefresh is released.
bne loop11
ldr r2, =0x201000 ; offset into the RAM
add r2, r2, #0x30000000 ; add physical base
mov pc, r2 ; & jump to StartUp address
nop
nop
nop
b .
这段程序的意义，就是恢复CPU的时钟，开启RAM的自刷新然后跳转到 RAM中的一个地址去执行，这个地址是0x32001000。那么熟悉2440 WINCE启动的朋友们应该明白了，这个地址就是Bootloader把NandFlash里的数据装载完毕后，跳转执行的地址。那么在这里，跳转到0x30201000这个地址后，WINCE系统就会被装载了，也就是说WINCE的操作系统被唤醒了。(全文完)
