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//注意：在上一篇Nor Flash启动中，我们为了把u-boot用supervivi下载到内存中运行而屏蔽掉这段有关CPU初始化的代码。而现在我们要把u-boot下载到Nand Flash中，从Nand Flash启动，所以现在要恢复这段代码。
#ifndef CONFIG_SKIP_LOWLEVEL_INIT
bl cpu_init_crit
#endif
#if 0
//屏蔽掉u-boot中的从Nor Flash启动部分
#ifndef CONFIG_SKIP_RELOCATE_UBOOT
relocate: /* relocate U-Boot to RAM */
adr r0, _start /* r0 <- current position of code */
ldr r1, _TEXT_BASE /* test if we run from flash or RAM */
cmp r0, r1 /* don't reloc during debug */
beq stack_setup
ldr r2, _armboot_start
ldr r3, _bss_start
sub r2, r3, r2 /* r2 <- size of armboot */
add r2, r0, r2 /* r2 <- source end address */
copy_loop:
ldmia r0!, {r3-r10} /* copy from source address [r0] */
stmia r1!, {r3-r10} /* copy to target address [r1] */
cmp r0, r2 /* until source end addreee [r2] */
ble copy_loop
#endif /* CONFIG_SKIP_RELOCATE_UBOOT */
#endif
//下面添加2440中u-boot从Nand Flash启动
#ifdef CONFIG_S3C2440_NAND_BOOT
mov r1, #NAND_CTL_BASE //复位Nand Flash
ldr r2, =( (7<<12)|(7<<8)|(7<<4)|(0<<0) )
str r2, [r1, #oNFCONF] //设置配置寄存器的初始值，参考s3c2440手册
ldr r2, [r1, #oNFCONF]
ldr r2, =( (1<<4)|(0<<1)|(1<<0) )
str r2, [r1, #oNFCONT] //设置控制寄存器
ldr r2, [r1, #oNFCONT]
ldr r2, =(0x6) //RnB Clear
str r2, [r1, #oNFSTAT]
ldr r2, [r1, #oNFSTAT]
mov r2, #0xff //复位command
strb r2, [r1, #oNFCMD]
mov r3, #0 //等待
nand1:
add r3, r3, #0x1
cmp r3, #0xa
blt nand1
nand2:
ldr r2, [r1, #oNFSTAT] //等待就绪
tst r2, #0x4
beq nand2
ldr r2, [r1, #oNFCONT]
orr r2, r2, #0x2 //取消片选
str r2, [r1, #oNFCONT]
//get read to call C functions (for nand_read())
ldr sp, DW_STACK_START //为C代码准备堆栈,DW_STACK_START定义在下面
mov fp, #0
//copy U-Boot to RAM
ldr r0, =TEXT_BASE//传递给C代码的第一个参数：u-boot在RAM中的起始地址
mov r1, #0x0 //传递给C代码的第二个参数：Nand Flash的起始地址
mov r2, #0x30000 //传递给C代码的第三个参数：u-boot的长度大小(128k)
bl nand_read_ll //此处调用C代码中读Nand的函数，现在还没有要自己编写实现
tst r0, #0x0
beq ok_nand_read
bad_nand_read:
loop2: b loop2 //infinite loop
ok_nand_read:
//
检查搬移后的数据，如果前4k完全相同，表示搬移成功
mov r0, #0
ldr r1, =TEXT_BASE
mov r2, #0x400 //4 bytes * 1024 = 4K-bytes
go_next:
ldr r3, [r0], #4
ldr r4, [r1], #4
teq r3, r4
bne notmatch
subs r2, r2, #4
beq stack_setup
bne go_next
notmatch:
loop3: b loop3 //infinite loop
#endif //CONFIG_S3C2440_NAND_BOOT
_start_armboot: .word start_armboot //在这一句的下面加上DW_STACK_START的定义
.align 2
DW_STACK_START: .word STACK_BASE+STACK_SIZE-4
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