bootload启动流程（一）－－－－硬件的初始化和基本配置

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EBOOT经过NBOOT引导后，一般会跳转到0x30038000开始执行第一条指令。在我这EBOOT中是先执行目录下2440/Kernel/hal/arm/fw.s。这个在有些系统能够中是setup.s，总之就是从系统ResetHandle开始执行了。下面开始分析这段汇编代码，并且讲述它都做了一些什么工作：

ldr r0, = INTMSK

ldr r1, = ~BIT_BAT_FLT ; all interrupt disable, nBATT_FLT =enabled

str r1, [r0]

ldr r0, = INTSUBMSK

ldr r1, = 0x7ff ;all sub interrupt disable

str r1, [r0]

ldr r0, = INTMOD

ldr r1, = BIT_BAT_FLT ; set all interrupt as IRQ, BAT_FLT = FIQ

str r1, [r0]

ldr r1, =MISCCR ; MISCCR's Bit [22:20] -> 100

ldr r0, [r1]

bic r0, r0, #(7 << 20)

bic r0, r0, #(1 << 3)

bic r0, r0, #(1 << 13)

orr r0, r0, #(4 << 20)

str r0, [r1]

bl ARMClearUTLB

bl ARMFlushICache

ldr r0, = (DCACHE_LINES_PER_SET - 1)

ldr r1, = (DCACHE_NUM_SETS - 1)

ldr r2, = DCACHE_SET_INDEX_BIT

ldr r3, = DCACHE_LINE_SIZE

bl ARMFlushDCache

nop

ldr r0, = GPFCON

ldr r1, = 0x55aa

str r1, [r0]

ldr r0, = WTCON ; watch dog disable

ldr r1, = 0x0

str r1, [r0]

//以上代码比较简单，但是很关键，关闭所有中断，刷新cache和快表。后面是点亮LED，禁止看门狗。

[ {TRUE}

ldr r0, = CLKDIVN

ldr r1, = CLKDIVVAL ; 0x0 = 1:1:1 , 0x1 = 1:1:2, use CLKDIVVAL instead of 7

; 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]

ands r1, r1, #0xe ; Make AsyncBusMode

beq %F1

mrc p15, 0, r0, c1, c0, 0

orr r0, r0, #R1_nF:OR:R1_iA

mcr p15, 0, r0, c1, c0, 0

ldr r0, = LOCKTIME ; To reduce PLL lock time, adjust the LOCKTIME register.

ldr r1, = 0xffffff

str r1, [r0]

ldr r0, = UPLLCON ; Fin=12MHz, Fout=48MHz

[ FIN = 12

ldr r1, = ((0x38 << 12) + (0x2 << 4) + 0x2)

ldr r1, = ((60 << 12) + (4 << 4) + 0x2)

]

str r1, [r0]

nop ; Caution: After UPLL setting, at least 7-clocks delay must be inserted for setting hardware be completed.

nop

ldr r0, = CAMDIVN

ldr r1, = 0

str r1, [r0]

ldr r0, = MPLLCON ; Configure MPLL ; Fin=12MHz, Fout=50MHz

ldr r1, = PLLVAL

str r1, [r0]

]

mov r0, #0x2000

subs r0, r0, #1

bne %B1

//以上的也同样简单但是很重要，主要是设置总线时钟比，启动PLL和UPLL然后等待有效。

下面的代码也是一些电源管理，检测启动模式（电源启动、睡眠启动还是看门狗启动），最后初始化内存一直到下面的代码：

; :::::::::::::::::::::::::::::::::::::::::::::

; Add for Power Management

; - - - - - - - - - - - - - - - - - - - - - - -

tst r10, #0x2 ; Power-Off reset check

beq BringUpWinCE ; Normal Mode Booting

如果检测到是正常启动，则跳到BringUpWinCE：

BringUpWinCE

ldr r0, = GPFDAT

mov r1, #0x60

str r1, [r0]

add r0, pc, #OEMAddressTable - (. + 8)

bl KernelStart

到这之后点亮指示灯后将map的头指针给r0后进入内核启动，实际这段代码是nk和Boot公用的。这里只讨论boot，所以代码进去了mmu.s:

这个代码在2440/eboot /arm/mmu.s下面：

; (r10) = 1st level page table

; (r11) = ptr to MemoryMap array

add r10, r10, #0x2000 ; (r10) = ptr to 1st PTE for "unmapped space"

mov r0, #0x0E ; (r0) = PTE for 0: 1MB cachable bufferable

orr r0, r0, #0x400 ; set kernel r/w permission

20 mov r1, r11 ; (r1) = ptr to MemoryMap array

25 ldr r2, [r1], #4 ; (r2) = virtual address to map Bank at

ldr r3, [r1], #4 ; (r3) = physical address to map from

ldr r4, [r1], #4 ; (r4) = num MB to map

cmp r4, #0 ; End of table?

beq %F29

ldr r5, =0x1FF00000

and r2, r2, r5 ; VA needs 512MB, 1MB aligned.

ldr r5, =0xFFF00000

and r3, r3, r5 ; PA needs 4GB, 1MB aligned.

add r2, r10, r2, LSR #18

add r0, r0, r3 ; (r0) = PTE for next physical page

28 str r0, [r2], #4

add r0, r0, #0x00100000 ; (r0) = PTE for next physical page

sub r4, r4, #1 ; Decrement number of MB left

cmp r4, #0

bne %B28 ; Map next MB

bic r0, r0, #0xF0000000 ; Clear Section Base Address Field

bic r0, r0, #0x0FF00000 ; Clear Section Base Address Field

b %B25 ; Get next element

29 tst r0, #8

bic r0, r0, #0x0C ; clear cachable & bufferable bits in PTE

add r10, r10, #0x0800 ; (r10) = ptr to 1st PTE for "unmapped uncached space"

bne %B20 ; go setup PTEs for uncached space

sub r10, r10, #0x3000 ; (r10) = restore address of 1st level page table

; setup mmu to map (VA == 0) to (PA == 0x30000000)

ldr r0, =PTs ; PTE entry for VA = 0

ldr r1, =0x3000040E ; uncache/unbuffer/rw, PA base == 0x30000000

str r1, [r0]

; uncached area

add r0, r0, #0x0800 ; PTE entry for VA = 0x0200.0000 , uncached

ldr r1, =0x30000402 ; uncache/unbuffer/rw, base == 0x30000000

str r1, [r0]

; Comment:

; The following loop is to direct map RAM VA == PA. i.e.

; VA == 0x30XXXXXX => PA == 0x30XXXXXX for S3C2400

; Fill in 8 entries to have a direct mapping for DRAM

ldr r10, =PTs ; restore address of 1st level page table

ldr r0, =PHYBASE

add r10, r10, #(0x3000 / 4) ; (r10) = ptr to 1st PTE for 0x30000000

add r0, r0, #0x1E ; 1MB cachable bufferable

orr r0, r0, #0x400 ; set kernel r/w permission

mov r1, #0

mov r3, #64

35 mov r2, r1 ; (r2) = virtual address to map Bank at

cmp r2, #0x20000000:SHR:BANK_SHIFT

add r2, r10, r2, LSL #BANK_SHIFT-18

strlo r0, [r2]

add r0, r0, #0x00100000 ; (r0) = PTE for next physical page

subs r3, r3, #1

add r1, r1, #1

bgt %B35

ldr r10, =PTs ; (r10) = restore address of 1st level page table

;

; The page tables and exception vectors are setup. Initialize the MMU and turn

; it on.

mov r1, #1

MTC15 r1, c3 ; setup access to domain 0

MTC15 r10, c2

mcr p15, 0, r0, c8, c7, 0 ; flush I+D TLBs

mov r1, #0x0071 ; Enable: MMU

orr r1, r1, #0x0004 ; Enable the cache

ldr r0, =VirtualStart

cmp r0, #0 ; make sure no stall on "mov pc,r0" below

MTC15 r1, c1 ; enable the MMU & Caches

mov pc, r0 ; & jump to new virtual address

nop

; MMU & caches now enabled.

;

; (r10) = physcial address of 1st level page table

VirtualStart

mov sp, #0x8C000000

add sp, sp, #0x30000 ; arbitrary initial super-page stack pointer

b main

END

上面的代码实际也很简单，主要工作是初始化页表，这里因为是Boot，所以只初始化了一级页表和开启了mmu。关于这段代码的详细分析我写了一片关于mmu的文章，有兴趣的朋友可以查阅。最后跳转到main()，这里就进入了真正的c代码。(待续。。)