code

comments

.globl _start

_start: b    reset

ldr    pc, _undefined_instruction

ldr    pc, _software_interrupt

ldr    pc, _prefetch_abort

ldr    pc, _data_abort

ldr    pc, _not_used

ldr    pc, _irq

ldr    pc, _fiq

_undefined_instruction: .word undefined_instruction

_software_interrupt:    .word software_interrupt

_prefetch_abort:    .word prefetch_abort

_data_abort:        .word data_abort

_not_used:        .word not_used

_irq:            .word irq

_fiq:            .word fiq

_pad:            .word 0x12345678 /* now 16*4=64 */

.global _end_vect

_end_vect:

.balignl
16,0xdeadbeef

初始化中断向量表 (Initialize exception vectors)

中断向量表

reset:

bl    save_boot_params

/*

* disable interrupts (FIQ and IRQ), also set
the cpu to SVC32 mode,

* except if in HYP mode already

*/

mrs    r0, cpsr

and    r1, r0, #0x1f        @ mask mode bits

teq    r1, #0x1a        @ test for HYP mode

bicne    r0, r0, #0x1f        @ clear all mode bits

orrne    r0, r0, #0x13        @ set SVC mode

orr    r0, r0, #0xc0        @ disable FIQ and IRQ

msr    cpsr,r0

禁止中断 (FIQ and IRQ), 设置CPU模式为SVC32 (Initialize core mode stacks and registers.)

/* Set
V=0 in CP15 SCTRL register - for VBAR to point to vector */

mrc    p15, 0, r0, c1, c0, 0    @ Read CP15 SCTRL Register

bic    r0, #CR_V        @ V = 0

mcr    p15, 0, r0, c1, c0, 0    @ Write CP15 SCTRL Register

/* Set
vector address in CP15 VBAR register */

ldr    r0, =_start

mcr    p15, 0, r0, c12, c0, 0    @Set VBAR

设置中断向量表 (Initialize exception vectors)

ENTRY(cpu_init_cp15)

/*

* Invalidate L1 I/D

*/

mov    r0, #0            @ set up for MCR

mcr    p15, 0, r0, c8, c7, 0    @ invalidate TLBs

mcr    p15, 0, r0, c7, c5, 0    @ invalidate icache

mcr    p15, 0, r0, c7, c5, 6    @ invalidate BP array

mcr     p15, 0, r0, c7, c10, 4    @ DSB

mcr     p15, 0, r0, c7, c5, 4    @ ISB

Invalidate L1 I/D cache (Initialize
the memory system, including the MMU)

/*

* disable MMU stuff and caches

*/

mrc    p15, 0, r0, c1, c0, 0

bic    r0, r0, #0x00002000    @ clear bits 13 (--V-)

bic    r0, r0, #0x00000007    @ clear bits 2:0 (-CAM)

orr    r0, r0, #0x00000002    @ set bit 1 (--A-) Align

orr    r0, r0, #0x00000800    @ set bit 11 (Z---) BTB

orr    r0, r0, #0x00001000    @ set bit 12 (I) I-cache

mcr    p15, 0, r0, c1, c0, 0

mov    pc, lr            @ back to my caller

禁止 MMU and caches (Initialize
the memory system, including the MMU)

ENTRY(_main)

/*

* Set up
initial C runtime environment and call board_init_f(0).

*/

ldr    sp, =(CONFIG_SYS_INIT_SP_ADDR)

bic    sp, sp, #7    /* 8-byte alignment for ABI compliance */

sub    sp, #GD_SIZE    /* allocate one GD above SP */

bic    sp, sp, #7    /* 8-byte alignment for ABI compliance */

mov    r9, sp        /* GD is above SP */

设置C运行环境 (Initialize core mode stacks and registers.)

mov    r0, #0

bl    board_init_f

调用 board_init_f(0) 对串口进行初始化(Initialize any critical I/O devices)

/*

* Set up
intermediate environment (new sp and gd) and call

*
relocate_code(addr_moni). Trick here is that we'll return

* 'here' but
relocated.

*/

ldr    sp, [r9, #GD_START_ADDR_SP]     /* sp = gd->start_addr_sp */

bic    sp, sp, #7    /* 8-byte alignment for ABI compliance */

ldr    r9, [r9, #GD_BD]        /* r9 = gd->bd */

sub    r9, r9, #GD_SIZE        /* new GD is below bd */

设置临时运行环境

adr    lr, here

ldr    r0, [r9, #GD_RELOC_OFF]     /*
r0 = gd->reloc_off */

add    lr, lr, r0

ldr    r0, [r9, #GD_RELOCADDR]     /*
r0 = gd->relocaddr */

b    relocate_code

here:

代码重定向，保证u-boot迁入内存后能够正常运行 (Relocate the code）

ENTRY(c_runtime_cpu_setup)

/*

* invalidate
I-cache

*/

mcr     p15, 0, r0, c7, c5, 0    @ invalidate icache

mcr     p15, 0, r0, c7, c10, 4    @ DSB

mcr     p15, 0, r0, c7, c5, 4    @ ISB

这几步操作前面已经进行过，感觉可以去掉

/*

* Move
vector table

*/

/* Set
vector address in CP15 VBAR register */

ldr     r0, =_start

mcr     p15, 0, r0, c12, c0, 0  @Set VBAR

This is auto-relocated!

This is useful, cause the u-boot has been moved
from ROM to RAM, the address of _start has changed.

The reall assembly code is below:

由于u-boot经过了重定向，代码位置发生了改变，所以这里需要重新设置VBAR寄存器。

实际的代码如下：

ldr    r0, [pc, #736]

利用PC保证加载的是当前地址，而不是u-boot在ROM中的地址。

ldr    r0,
=__bss_start    /* this is
auto-relocated! */

ldr    r1, =__bss_end    /* this is auto-relocated! */

mov    r2, #0x00000000    /* prepare zero to clear BSS */

clbss_l:cmp    r0, r1        /* while not at
end of BSS */

strlo    r2, [r0]        /* clear 32-bit BSS word */

addlo    r0, r0, #4        /* move to next */

blo    clbss_l

把 .bss 段清零

/* call
board_init_r(gd_t *id, ulong dest_addr) */

mov     r0, r9                  /* gd_t */

ldr    r1, [r9, #GD_RELOCADDR]    /* dest_addr */

/* call
board_init_r */

ldr    pc, =board_init_r    /* this is auto-relocated! */

调用 board_init_r(gd_t *id,
ulong dest_addr它会初始化网口设备，然后调用main_loop进入u-boot控制台。(Call
the main()application)

function

comments

arch_cpu_init

Do nothing on smdkc210

timer_init

Do nothing on smdkc210

env_init

初始化环境变量， 实际上是把default_environment设置到gd->env_addr.  default_environment是一个字符串数组，每一个字符串用一个宏表示，我们通过在“include/configs/smdkc210.h”定义这些宏的方式设置环境变量。

init_baudrate

设置波特率，其实它来自于 gd->baud.

serial_init

调用串口初始化函数

dram_init

设置RAM位置与大小

Set gd.

The most 设置gd表，用于保存配置