嵌入式学习笔记101-uboot_1.1.6移植（1）

1. 根据前篇博文（嵌入式学习笔记100-uboot1.1.6初体验）最后的结论，现在开始将其实现：
   a. 修改makefile的CROSS_COMPILE指定编译器

   1. arm-linux-gcc -v –> gcc version 3.4.5
   2. CROSS_COMPILE = /opt/EmbedSky/crosstools_3.4.5_softfloat/gcc-3.4.5-glibc-2.3.6/arm-linux/bin/arm-linux-
   3. chmod -R 777 u-boot-1.1.6/

   b. 在makefile里增加类似该配置
   1.tq2440_config : unconfig
   @$(MKCONFIG)$(@:_config=) arm arm920t tq2440 NULL s3c24x0

   c. 在board目录下新增板子的名称为目录

   1. cd board/
   2. cp -ar smdk2410/ tq2440
   3. mv smdk2410.c tq2440.c
   4. Makefile smdk2410.o –> tq2440.o

   d. 在include/configs下新增板子的头文件，文件名是配置第一个参数名

   1. cd include/configs/
   2. cp smdk2410.h tq2440.h

   e. make xxx_config 配置板子

   1. make tq2440_config –> Configuring for tq2440 board…

   f. make all 编译配置信息

   1. make all –> 会在跟目录生成bin等文件

2. 启动流程分析：
   a.删除不必要的文件以免干扰
   根目录下lib开头的库，其中保留lib_arm lib_generic
   删除board下除smdk2410 和tq2440 外所有文件
   删除include下除asm-arm外的asm-xx目录 include下configs下除smdk2410.h 和tq2440.h外的所有头文件
   删除cpu下除arm920t外所有的cpu
   重新建立一个新的project或者在原有的project sync

   b.第一阶段code分析

/*
 *  armboot - Startup Code for ARM920 CPU-core
 *
 *  Copyright (c) 2001  Marius Gr鰃er <mag@sysgo.de>
 *  Copyright (c) 2002  Alex Z黳ke <azu@sysgo.de>
 *  Copyright (c) 2002  Gary Jennejohn <gj@denx.de>
 *
 * See file CREDITS for list of people who contributed to this
 * project.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of
 * the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 * MA 02111-1307 USA
 */


#include <config.h>
#include <version.h>
/*============ ===  代码分析======================
*
*还记得P28的config.h怎么来的么，前篇博文有提到
*mkconfig 会在include下生成config.h，最终里面指向
*#include <configs/tq2440.h>，所以接下来的很多宏定义都是
*在include/configs/tq2440.h里定义的
*
*=================================================*/


/*
 *************************************************************************
 *
 * Jump vector table as in table 3.1 in [1]
 *
 *************************************************************************
 */


.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

    .balignl 16,0xdeadbeef

/*============ ===  代码分析======================
*
*P41-P57 主要设置了中断和异常的向量
*对应的处理函数其实除了IRQ,FIQ其他并没有做啥
*
*=================================================*/
/*
 *************************************************************************
 *
 * Startup Code (reset vector)
 *
 * do important init only if we don‘t start from memory!
 * relocate armboot to ram
 * setup stack
 * jump to second stage
 *
 *************************************************************************
 */

_TEXT_BASE:
    .word   TEXT_BASE

.globl _armboot_start
_armboot_start:
    .word _start

/*
 * These are defined in the board-specific linker script.
 */
.globl _bss_start
_bss_start:
    .word __bss_start

.globl _bss_end
_bss_end:
    .word _end

#ifdef CONFIG_USE_IRQ
/* IRQ stack memory (calculated at run-time) */
.globl IRQ_STACK_START
IRQ_STACK_START:
    .word   0x0badc0de

/* IRQ stack memory (calculated at run-time) */
.globl FIQ_STACK_START
FIQ_STACK_START:
    .word 0x0badc0de
#endif

/*============ ===  代码分析======================
*
*很明显想要使能IRQ/FIQ的话要在tq2440.h里
*定义这个CONFIG_USE_IRQ，不过stack的值就不是
*这个0x0badc0de，要更改成合适的
*
*=================================================*/


/*
 * the actual reset code
 */

reset:
    /*
     * set the cpu to SVC32 mode
     */
    mrs r0,cpsr
    bic r0,r0,#0x1f
    orr r0,r0,#0xd3
    msr cpsr,r0

/* turn off the watchdog */
#if defined(CONFIG_S3C2400)
# define pWTCON     0x15300000
# define INTMSK     0x14400008  /* Interupt-Controller base addresses */
# define CLKDIVN    0x14800014  /* clock divisor register */
#elif defined(CONFIG_S3C2410)
# define pWTCON     0x53000000
# define INTMSK     0x4A000008  /* Interupt-Controller base addresses */
# define INTSUBMSK  0x4A00001C
# define CLKDIVN    0x4C000014  /* clock divisor register */
#endif

#if defined(CONFIG_S3C2400) || defined(CONFIG_S3C2410)
    ldr     r0, =pWTCON
    mov     r1, #0x0
    str     r1, [r0]

    /*
     * mask all IRQs by setting all bits in the INTMR - default
     */
    mov r1, #0xffffffff
    ldr r0, =INTMSK
    str r1, [r0]
# if defined(CONFIG_S3C2410)
    ldr r1, =0x3ff
    ldr r0, =INTSUBMSK
    str r1, [r0]
# endif

    /* FCLK:HCLK:PCLK = 1:2:4 */
    /* default FCLK is 120 MHz ! */
    ldr r0, =CLKDIVN
    mov r1, #3
    str r1, [r0]
#endif  /* CONFIG_S3C2400 || CONFIG_S3C2410 */

/*============ ===  代码分析======================
*
*P131-P174无非就是跟之前裸奔程序一样
*关闭看门狗，设置时钟和中断
*
*=================================================*/


    /*
     * we do sys-critical inits only at reboot,
     * not when booting from ram!
     */
#ifndef CONFIG_SKIP_LOWLEVEL_INIT
    bl  cpu_init_crit
#endif

/*============ ===  代码分析======================
*
*P188-P190会做一次系统更基本的初始化
*根据上面的注释可知如果是直接从RAM
*启动的话不能调用cpu_init_crit 因为他会对RAM做
*清零的动作，code download到RAM结果自己清自己
*明显不行，否则程序跑到cpu_init_crit就挂了
*
*=================================================*/

#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 */

/*============ ===  代码分析======================
*
*P202-P219会判断此时正在跑的code是否就是指定的地址
*其中adr  r0, _start的用法就是获得真正的运行地址
*比如_start会等于board/tq2440/config.mk 
* TEXT_BASE = 0x33F80000
*但是程序刚跑是前面的博文讲过PC是从0开始+4的，所以
*地址无关的PC减去_start偏移最后_start=0,而
*_TEXT_BASE = 0x33F80000，所以会执行后面的copy动作，
*如果我们直接将code download到RAM的0x33F80000处，这部分的
*code则相当于无效
*
*=================================================*/



    /* Set up the stack                         */
stack_setup:
    ldr r0, _TEXT_BASE      /* upper 128 KiB: relocated uboot   */
    sub r0, r0, #CFG_MALLOC_LEN /* malloc area                      */
    sub r0, r0, #CFG_GBL_DATA_SIZE /* bdinfo                        */
#ifdef CONFIG_USE_IRQ
    sub r0, r0, #(CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ)
#endif
    sub sp, r0, #12     /* leave 3 words for abort-stack    */

/*============ ===  代码分析======================
*
*P237-P245跟之前的裸奔一样设置好栈，为第二阶段的C准备
*这里需要注意的是，由于栈是对_TEXT_BASE往下偏移的，这就
*要求_TEXT_BASE不能为RAM的基址，如果将_TEXT_BASE设置成
*0x30000000，那再往下就不是RAM了! 这是要注意的，同时_TEXT_BASE
*下还作为CFG_MALLOC_LEN的buffer，CFG_GBL_DATA_SIZE等用于
*传给linux的参数
*
*=================================================*/


clear_bss:
    ldr r0, _bss_start      /* find start of bss segment        */
    ldr r1, _bss_end        /* stop here                        */
    mov     r2, #0x00000000     /* clear                            */

clbss_l:str r2, [r0]        /* clear loop...                    */
    add r0, r0, #4
    cmp r0, r1
    ble clbss_l

#if 0
    /* try doing this stuff after the relocation */
    ldr     r0, =pWTCON
    mov     r1, #0x0
    str     r1, [r0]

    /*
     * mask all IRQs by setting all bits in the INTMR - default
     */
    mov r1, #0xffffffff
    ldr r0, =INTMR
    str r1, [r0]

    /* FCLK:HCLK:PCLK = 1:2:4 */
    /* default FCLK is 120 MHz ! */
    ldr r0, =CLKDIVN
    mov r1, #3
    str r1, [r0]
    /* END stuff after relocation */
#endif

    ldr pc, _start_armboot

_start_armboot: .word start_armboot

/*============ ===  代码分析======================
*
*设置好栈后直接调用_start_armboot，由于采用的是
*ldr    pc, _start_armboot ldr是赋值绝对地址，最终导致
*跑到运行地址处
*
*=================================================*/


/*
 *************************************************************************
 *
 * CPU_init_critical registers
 *
 * setup important registers
 * setup memory timing
 *
 *************************************************************************
 */


#ifndef CONFIG_SKIP_LOWLEVEL_INIT
cpu_init_crit:
    /*
     * flush v4 I/D caches
     */
    mov r0, #0
    mcr p15, 0, r0, c7, c7, 0   /* flush v3/v4 cache */
    mcr p15, 0, r0, c8, c7, 0   /* flush v4 TLB */

    /*
     * disable MMU stuff and caches
     */
    mrc p15, 0, r0, c1, c0, 0
    bic r0, r0, #0x00002300 @ clear bits 13, 9:8 (--V- --RS)
    bic r0, r0, #0x00000087 @ clear bits 7, 2:0 (B--- -CAM)
    orr r0, r0, #0x00000002 @ set bit 2 (A) Align
    orr r0, r0, #0x00001000 @ set bit 12 (I) I-Cache
    mcr p15, 0, r0, c1, c0, 0

    /*
     * before relocating, we have to setup RAM timing
     * because memory timing is board-dependend, you will
     * find a lowlevel_init.S in your board directory.
     */
    mov ip, lr
    bl  lowlevel_init
    mov lr, ip
    mov pc, lr
#endif /* CONFIG_SKIP_LOWLEVEL_INIT */

/*
 *************************************************************************
 *
 * Interrupt handling
 *
 *************************************************************************
 */

@
@ IRQ stack frame.
@
#define S_FRAME_SIZE    72

#define S_OLD_R0    68
#define S_PSR       64
#define S_PC        60
#define S_LR        56
#define S_SP        52

#define S_IP        48
#define S_FP        44
#define S_R10       40
#define S_R9        36
#define S_R8        32
#define S_R7        28
#define S_R6        24
#define S_R5        20
#define S_R4        16
#define S_R3        12
#define S_R2        8
#define S_R1        4
#define S_R0        0

#define MODE_SVC 0x13
#define I_BIT    0x80

/*
 * use bad_save_user_regs for abort/prefetch/undef/swi ...
 * use irq_save_user_regs / irq_restore_user_regs for IRQ/FIQ handling
 */

    .macro  bad_save_user_regs
    sub sp, sp, #S_FRAME_SIZE
    stmia   sp, {r0 - r12}          @ Calling r0-r12
    ldr r2, _armboot_start
    sub r2, r2, #(CONFIG_STACKSIZE+CFG_MALLOC_LEN)
    sub r2, r2, #(CFG_GBL_DATA_SIZE+8)  @ set base 2 words into abort stack
    ldmia   r2, {r2 - r3}           @ get pc, cpsr
    add r0, sp, #S_FRAME_SIZE       @ restore sp_SVC

    add r5, sp, #S_SP
    mov r1, lr
    stmia   r5, {r0 - r3}           @ save sp_SVC, lr_SVC, pc, cpsr
    mov r0, sp
    .endm

    .macro  irq_save_user_regs
    sub sp, sp, #S_FRAME_SIZE
    stmia   sp, {r0 - r12}          @ Calling r0-r12
    add     r8, sp, #S_PC
    stmdb   r8, {sp, lr}^                   @ Calling SP, LR
    str     lr, [r8, #0]                    @ Save calling PC
    mrs     r6, spsr
    str     r6, [r8, #4]                    @ Save CPSR
    str     r0, [r8, #8]                    @ Save OLD_R0
    mov r0, sp
    .endm

    .macro  irq_restore_user_regs
    ldmia   sp, {r0 - lr}^          @ Calling r0 - lr
    mov r0, r0
    ldr lr, [sp, #S_PC]         @ Get PC
    add sp, sp, #S_FRAME_SIZE
    subs    pc, lr, #4          @ return & move spsr_svc into cpsr
    .endm

    .macro get_bad_stack
    ldr r13, _armboot_start     @ setup our mode stack
    sub r13, r13, #(CONFIG_STACKSIZE+CFG_MALLOC_LEN)
    sub r13, r13, #(CFG_GBL_DATA_SIZE+8) @ reserved a couple spots in abort stack

    str lr, [r13]           @ save caller lr / spsr
    mrs lr, spsr
    str     lr, [r13, #4]

    mov r13, #MODE_SVC          @ prepare SVC-Mode
    @ msr   spsr_c, r13
    msr spsr, r13
    mov lr, pc
    movs    pc, lr
    .endm

    .macro get_irq_stack            @ setup IRQ stack
    ldr sp, IRQ_STACK_START
    .endm

    .macro get_fiq_stack            @ setup FIQ stack
    ldr sp, FIQ_STACK_START
    .endm

/*
 * exception handlers
 */
    .align  5
undefined_instruction:
    get_bad_stack
    bad_save_user_regs
    bl  do_undefined_instruction

    .align  5
software_interrupt:
    get_bad_stack
    bad_save_user_regs
    bl  do_software_interrupt

    .align  5
prefetch_abort:
    get_bad_stack
    bad_save_user_regs
    bl  do_prefetch_abort

    .align  5
data_abort:
    get_bad_stack
    bad_save_user_regs
    bl  do_data_abort

    .align  5
not_used:
    get_bad_stack
    bad_save_user_regs
    bl  do_not_used

#ifdef CONFIG_USE_IRQ

    .align  5
irq:
    get_irq_stack
    irq_save_user_regs
    bl  do_irq
    irq_restore_user_regs

    .align  5
fiq:
    get_fiq_stack
    /* someone ought to write a more effiction fiq_save_user_regs */
    irq_save_user_regs
    bl  do_fiq
    irq_restore_user_regs

#else

    .align  5
irq:
    get_bad_stack
    bad_save_user_regs
    bl  do_irq

    .align  5
fiq:
    get_bad_stack
    bad_save_user_regs
    bl  do_fiq

#endif