Linux学习 ： 自己写bootloader

一、bootloader 目标：启动内核

基本功能：

　　①初始化硬件：关看门狗、设置时钟、设置SDRAM、初始化NAND FLASH

　　②image比较大需要重定位到SDRAM

　　②将内核从NAND FLASH读到 SDRAM

　　③设置“要传给内核的参数”

　　④跳转执行内核

启动时间优化：

　　①提高CPU频率:

　　　　   1，FCLK是CPU提供的时钟信号。
      　  　2，HCLK是为AHB总线提供的时钟信号， Advanced High-performance Bus，主要用于高速外设，比如内存控制器，中断控制器，LCD控制器， DMA 等。
    　　    3，PCLK是为APB总线提供的时钟信号，Advanced Peripherals Bus，主要用于低速外设，比如看门狗，UART控制器， IIS, I2C， SDI/MMC, GPIO，RTC and SPI等。

　　②启动ICACHE:　

　　　　CPU将多条指令一次装入ICACHE,不用每次到SDRAM中去取指。
           另外，DCACHE主要用来取数据，需要启用MMU.

　　　　

1.start.S

#define S3C2440_MPLL_200MHZ     ((0x5c<<12)|(0x01<<4)|(0x02))
#define S3C2440_MPLL_400MHZ     ((0x5c<<12)|(0x01<<4)|(0x01))
#define MEM_CTL_BASE    0x48000000

.text
.global _start
_start:

/* 1. 关看门狗 */
    ldr r0, =0x53000000
    mov r1, #
    str r1, [r0]

/* 2. 设置时钟 */
    ldr r0, =0x4c000014
    //    mov r1, #0x03;              // FCLK:HCLK:PCLK=1:2:4, HDIVN=1,PDIVN=1
    mov r1, #0x05;              // FCLK:HCLK:PCLK=1:4:8
    str r1, [r0]

   /* 如果HDIVN非0，CPU的总线模式应该从“fast bus mode”变为“asynchronous bus mode” */
    mrc    p15, , r1, c1, c0,         /* 读出控制寄存器 */
    orr    r1, r1, #0xc0000000            /* 设置为“asynchronous bus mode” */
    mcr    p15, , r1, c1, c0,         /* 写入控制寄存器　*/

    /* MPLLCON = S3C2440_MPLL_200MHZ */
    ldr r0, =0x4c000004
    ldr r1, =S3C2440_MPLL_400MHZ
    str r1, [r0]

    /* 启动ICACHE */
    mrc p15, , r0, c1, c0,     @ read control reg 读协处理器
    orr r0, r0, #(<<)
    mcr    p15, , r0, c1, c0,    @ write it back　写入协处理器

/* 3. 初始化SDRAM */
    ldr r0, =MEM_CTL_BASE
    adr r1, sdram_config     /* sdram_config的当前地址 */
    add r3, r0, #(*)
:
    ldr r2, [r1], #
    str r2, [r0], #
    cmp r0, r3
    bne 1b

/* 4. 重定位 : 把bootloader本身的代码从flash复制到它的链接地址去 */
    ldr sp, =0x34000000

    bl nand_init

　　/* r0 r1 r2 表示给之后调用C函数传入的参数 */
    mov r0, #
    ldr r1, =_start
    ldr r2, =__bss_start  /*通过伪汇编获取bss段的结束地址*/
    sub r2, r2, r1

    bl copy_code_to_sdram
    bl clear_bss

/* 5. 执行main */
    ldr lr, =halt
    ldr pc, =main
halt:
    b halt

sdram_config:
    .long 0x22011110     //BWSCON
    .long 0x00000700     //BANKCON0
    .long 0x00000700     //BANKCON1
    .long 0x00000700     //BANKCON2
    .long 0x00000700     //BANKCON3
    .long 0x00000700     //BANKCON4
    .long 0x00000700     //BANKCON5
    .long 0x00018005     //BANKCON6
    .long 0x00018005     //BANKCON7
    .long 0x008C04F4     // REFRESH
    .long 0x000000B1     //BANKSIZE
    .long 0x00000030     //MRSRB6
    .long 0x00000030     //MRSRB7

2.init.c

/* NAND FLASH控制器 */
#define NFCONF (*((volatile unsigned long *)0x4E000000))
#define NFCONT (*((volatile unsigned long *)0x4E000004))
#define NFCMMD (*((volatile unsigned char *)0x4E000008))
#define NFADDR (*((puthexvolatile unsigned char *)0x4E00000C))
#define NFDATA (*((volatile unsigned char *)0x4E000010))
#define NFSTAT (*((volatile unsigned char *)0x4E000020))

/* GPIO */
#define GPHCON              (*(volatile unsigned long *)0x56000070)
#define GPHUP               (*(volatile unsigned long *)0x56000078)

/* UART registers*/
#define ULCON0              (*(volatile unsigned long *)0x50000000)
#define UCON0               (*(volatile unsigned long *)0x50000004)
#define UFCON0              (*(volatile unsigned long *)0x50000008)
#define UMCON0              (*(volatile unsigned long *)0x5000000c)
#define UTRSTAT0            (*(volatile unsigned long *)0x50000010)
#define UTXH0               (*(volatile unsigned char *)0x50000020)
#define URXH0               (*(volatile unsigned char *)0x50000024)
#define UBRDIV0             (*(volatile unsigned long *)0x50000028)

#define TXD0READY   (1<<2)

void nand_read(unsigned int addr, unsigned char *buf, unsigned int len);

int isBootFromNorFlash(void)
{
    volatile int *p = (volatile int *);
    int val;

    val = *p;
    *p = 0x12345678;
    if (*p == 0x12345678)
    {
        /* 写成功, 是nand启动 */
        *p = val;
        return ;
    }
    else
    {
        /* NOR不能像内存一样写 */
        return ;
    }
}

void copy_code_to_sdram(unsigned char *src, unsigned char *dest, unsigned int len)
{
    int i = ;

    /* 如果是NOR启动 */
    if (isBootFromNorFlash())
    {
        while (i < len)
        {
            dest[i] = src[i];
            i++;
        }
    }
    else
    {
        //nand_init();
        nand_read((unsigned int)src, dest, len);
    }
}

void clear_bss(void)
{
    extern int __bss_start, __bss_end;
    int *p = &__bss_start;

    for (; p < &__bss_end; p++)
        *p = ;
}

void nand_init(void)
{
#define TACLS   0
#define TWRPH0  1
#define TWRPH1  0
    /* 设置时序 */
    NFCONF = (TACLS<<)|(TWRPH0<<)|(TWRPH1<<);
    /* 使能NAND Flash控制器, 初始化ECC, 禁止片选 */
    NFCONT = (<<)|(<<)|(<<);
}

void nand_select(void)
{
    NFCONT &= ~(<<);
}

void nand_deselect(void)
{
    NFCONT |= (<<);
}

void nand_cmd(unsigned char cmd)
{
    volatile int i;
    NFCMMD = cmd;
    for (i = ; i < ; i++);
}

void nand_addr(unsigned int addr)
{
    unsigned int col  = addr % ;
    unsigned int page = addr / ;
    volatile int i;

    NFADDR = col & 0xff;
    for (i = ; i < ; i++);
    NFADDR = (col >> ) & 0xff;
    for (i = ; i < ; i++);

    NFADDR  = page & 0xff;
    for (i = ; i < ; i++);
    NFADDR  = (page >> ) & 0xff;
    for (i = ; i < ; i++);
    NFADDR  = (page >> ) & 0xff;
    for (i = ; i < ; i++);
}

void nand_wait_ready(void)
{
    while (!(NFSTAT & ));
}

unsigned char nand_data(void)
{
    return NFDATA;
}

void nand_read(unsigned int addr, unsigned char *buf, unsigned int len)
{
    int col = addr % ;
    int i = ;

    /* 1. 选中 */
    nand_select();

    while (i < len)
    {
        /* 2. 发出读命令00h */
        nand_cmd(0x00);

        /* 3. 发出地址(分5步发出) */
        nand_addr(addr);

        /* 4. 发出读命令30h */
        nand_cmd(0x30);

        /* 5. 判断状态 */
        nand_wait_ready();

        /* 6. 读数据 */
        for (; (col < ) && (i < len); col++)
        {
            buf[i] = nand_data();
            i++;
            addr++;
        }

        col = ;
    }

    /* 7. 取消选中 */
    nand_deselect();
}

#define PCLK            50000000    // init.c中的clock_init函数设置PCLK为50MHz
#define UART_CLK        PCLK        //  UART0的时钟源设为PCLK
#define UART_BAUD_RATE  115200      // 波特率
#define UART_BRD        ((UART_CLK  / (UART_BAUD_RATE * 16)) - 1)

/*
 * 初始化UART0
 * 115200,8N1,无流控
 */
void uart0_init(void)
{
    GPHCON  |= 0xa0;    // GPH2,GPH3用作TXD0,RXD0
    GPHUP   = 0x0c;     // GPH2,GPH3内部上拉

    ULCON0  = 0x03;     // 8N1(8个数据位，无较验，1个停止位)
    UCON0   = 0x05;     // 查询方式，UART时钟源为PCLK
    UFCON0  = 0x00;     // 不使用FIFO
    UMCON0  = 0x00;     // 不使用流控
    UBRDIV0 = UART_BRD; // 波特率为115200
}

/*
 * 发送一个字符
 */
void putc(unsigned char c)
{
    /* 等待，直到发送缓冲区中的数据已经全部发送出去 */
    while (!(UTRSTAT0 & TXD0READY));

    /* 向UTXH0寄存器中写入数据，UART即自动将它发送出去 */
    UTXH0 = c;
}

void puts(char *str)
{
    int i = ;
    while (str[i])
    {
        putc(str[i]);
        i++;
    }
}

void puthex(unsigned int val)
{
    /* 0x1234abcd */
    int i;
    int j;

    puts("0x");

    for (i = ; i < ; i++)
    {
        j = (val >> ((-i)*)) & 0xf;
        if ((j >= ) && (j <= ))
            putc('' + j);
        else
            putc('A' + j - 0xa);

    }

}

3.boot.c

#include "setup.h"

extern void uart0_init(void);
extern void nand_read(unsigned int addr, unsigned char *buf, unsigned int len);
extern void puts(char *str);
extern void puthex(unsigned int val);

static struct tag *params;

void setup_start_tag(void)
{
    params = (struct tag *)0x30000100;

    params->hdr.tag = ATAG_CORE; //0x54410001,表示参数的开始
    params->hdr.size = tag_size (tag_core);　//5个

    params->u.core.flags = ;
    params->u.core.pagesize = ;　
    params->u.core.rootdev = ;  

    params = tag_next (params);
}

void setup_memory_tags(void)
{
    params->hdr.tag = ATAG_MEM;
    params->hdr.size = tag_size (tag_mem32);

    params->u.mem.start = 0x30000000;
    params->u.mem.size  = **;　//64M

    params = tag_next (params);　//如分多个内存存放tag,用tag_next查找
}

int strlen(char *str)
{
    int i = ;
    while (str[i])
    {
        i++;
    }
    return i;
}

void strcpy(char *dest, char *src)
{
    while ((*dest++ = *src++) != '\0');
}

void setup_commandline_tag(char *cmdline)
{
    int len = strlen(cmdline) + ;

    params->hdr.tag  = ATAG_CMDLINE;
    params->hdr.size = (sizeof (struct tag_header) + len + ) >> ;　//向４取整

    strcpy (params->u.cmdline.cmdline, cmdline);　

    params = tag_next (params);
}

void setup_end_tag(void)
{
    params->hdr.tag = ATAG_NONE;
    params->hdr.size = ;
}

int main(void)
{
    void (*theKernel)(int zero, int arch, unsigned int params);
    volatile unsigned int *p = (volatile unsigned int *)0x30008000;

    /* 0. 帮内核设置串口: 内核启动的开始部分会从串口打印一些信息,但是内核一开始没有初始化串口 */
    uart0_init();

    /* 1. 从NAND FLASH里把内核读入内存 */
    puts("Copy kernel from nand\n\r");
    nand_read(0x60000+, (unsigned char *)0x30008000, 0x200000);
    puthex(0x1234ABCD);
    puts("\n\r");
    puthex(*p);
    puts("\n\r");

    /* 2. 设置参数 ，与内核约定参数存放地址，Uboot写个内核的遗嘱^^*/
    puts("Set boot params\n\r");
    setup_start_tag();
    setup_memory_tags();
    setup_commandline_tag("noinitrd root=/dev/mtdblock3 init=/linuxrc console=ttySAC0");
    setup_end_tag();

    /* 3. 跳转执行 */
    puts("Boot kernel\n\r");
    theKernel = (void (*)(int, int, unsigned int))0x30008000;
    theKernel(, , 0x30000100);  //362:arm
    /*
     *  mov r0, #0
     *  ldr r1, =362
     *  ldr r2, =0x30000100
     *  mov pc, #0x30008000
     */

    puts("Error!\n\r");
    /* 如果一切正常, 不会执行到这里 */

    return -;
}

4.boot.lds　　:   指定代码存放的位置

SECTIONS {
    . = 0x33f80000;  #与最高地址差512K
    .text : { *(.text) }

    . = ALIGN();
    .rodata : {*(.rodata*)} 

    . = ALIGN();
    .data : { *(.data) }

    . = ALIGN();
    __bss_start = .;  #bss段指向当前地址，保存未初始化或为0的全局变量
    .bss : { *(.bss)  *(COMMON) }
    __bss_end = .;　　 #bss段设定起始和结束地址，程序启动时统一初始化保存的变量
}

5.setup.h

/*
 *  linux/include/asm/setup.h
 *
 *  Copyright (C) 1997-1999 Russell King
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 *  Structure passed to kernel to tell it about the
 *  hardware it's running on.  See linux/Documentation/arm/Setup
 *  for more info.
 *
 * NOTE:
 *  This file contains two ways to pass information from the boot
 *  loader to the kernel. The old struct param_struct is deprecated,
 *  but it will be kept in the kernel for 5 years from now
 *  (2001). This will allow boot loaders to convert to the new struct
 *  tag way.
 */
#ifndef __ASMARM_SETUP_H
#define __ASMARM_SETUP_H

#define u8  unsigned char
#define u16 unsigned short
#define u32 unsigned long

/*
 * Usage:
 *  - do not go blindly adding fields, add them at the end
 *  - when adding fields, don't rely on the address until
 *    a patch from me has been released
 *  - unused fields should be zero (for future expansion)
 *  - this structure is relatively short-lived - only
 *    guaranteed to contain useful data in setup_arch()
 */
#define COMMAND_LINE_SIZE 1024

/* This is the old deprecated way to pass parameters to the kernel */
struct param_struct {
    union {
    struct {
        unsigned long page_size;        /*  0 */
        unsigned long nr_pages;        /*  4 */
        unsigned long ramdisk_size;        /*  8 */
        unsigned long flags;        /* 12 */
#define FLAG_READONLY    1
#define FLAG_RDLOAD    4
#define FLAG_RDPROMPT    8
        unsigned long rootdev;        /* 16 */
        unsigned long video_num_cols;    /* 20 */
        unsigned long video_num_rows;    /* 24 */
        unsigned long video_x;        /* 28 */
        unsigned long video_y;        /* 32 */
        unsigned long memc_control_reg;    /* 36 */
        unsigned char sounddefault;        /* 40 */
        unsigned char adfsdrives;        /* 41 */
        unsigned char bytes_per_char_h;    /* 42 */
        unsigned char bytes_per_char_v;    /* 43 */
        unsigned long pages_in_bank[];    /* 44 */
        unsigned long pages_in_vram;    /* 60 */
        unsigned long initrd_start;        /* 64 */
        unsigned long initrd_size;        /* 68 */
        unsigned long rd_start;        /* 72 */
        unsigned long system_rev;        /* 76 */
        unsigned long system_serial_low;    /* 80 */
        unsigned long system_serial_high;    /* 84 */
        unsigned long mem_fclk_21285;       /* 88 */
    } s;
    char unused[];
    } u1;
    union {
    char paths[][];
    struct {
        unsigned long magic;
        char n[ - sizeof(unsigned long)];
    } s;
    } u2;
    char commandline[COMMAND_LINE_SIZE];
};

/*
 * The new way of passing information: a list of tagged entries
 */

/* The list ends with an ATAG_NONE node. */
#define ATAG_NONE    0x00000000

struct tag_header {
    u32 size;
    u32 tag;
};

/* The list must start with an ATAG_CORE node */
#define ATAG_CORE    0x54410001

struct tag_core {
    u32 flags;        /* bit 0 = read-only */
    u32 pagesize;
    u32 rootdev;
};

/* it is allowed to have multiple ATAG_MEM nodes */
#define ATAG_MEM    0x54410002

struct tag_mem32 {
    u32    size;
    u32    start;    /* physical start address */
};

/* VGA text type displays */
#define ATAG_VIDEOTEXT    0x54410003

struct tag_videotext {
    u8        x;
    u8        y;
    u16        video_page;
    u8        video_mode;
    u8        video_cols;
    u16        video_ega_bx;
    u8        video_lines;
    u8        video_isvga;
    u16        video_points;
};

/* describes how the ramdisk will be used in kernel */
#define ATAG_RAMDISK    0x54410004

struct tag_ramdisk {
    u32 flags;    /* bit 0 = load, bit 1 = prompt */
    u32 size;    /* decompressed ramdisk size in _kilo_ bytes */
    u32 start;    /* starting block of floppy-based RAM disk image */
};

/* describes where the compressed ramdisk image lives (virtual address) */
/*
 * this one accidentally used virtual addresses - as such,
 * its depreciated.
 */
#define ATAG_INITRD    0x54410005

/* describes where the compressed ramdisk image lives (physical address) */
#define ATAG_INITRD2    0x54420005

struct tag_initrd {
    u32 start;    /* physical start address */
    u32 size;    /* size of compressed ramdisk image in bytes */
};

/* board serial number. "64 bits should be enough for everybody" */
#define ATAG_SERIAL    0x54410006

struct tag_serialnr {
    u32 low;
    u32 high;
};

/* board revision */
#define ATAG_REVISION    0x54410007

struct tag_revision {
    u32 rev;
};

/* initial values for vesafb-type framebuffers. see struct screen_info
 * in include/linux/tty.h
 */
#define ATAG_VIDEOLFB    0x54410008

struct tag_videolfb {
    u16        lfb_width;
    u16        lfb_height;
    u16        lfb_depth;
    u16        lfb_linelength;
    u32        lfb_base;
    u32        lfb_size;
    u8        red_size;
    u8        red_pos;
    u8        green_size;
    u8        green_pos;
    u8        blue_size;
    u8        blue_pos;
    u8        rsvd_size;
    u8        rsvd_pos;
};

/* command line: \0 terminated string */
#define ATAG_CMDLINE    0x54410009

struct tag_cmdline {
    char    cmdline[];    /* this is the minimum size */
};

/* acorn RiscPC specific information */
#define ATAG_ACORN    0x41000101

struct tag_acorn {
    u32 memc_control_reg;
    u32 vram_pages;
    u8 sounddefault;
    u8 adfsdrives;
};

/* footbridge memory clock, see arch/arm/mach-footbridge/arch.c */
#define ATAG_MEMCLK    0x41000402

struct tag_memclk {
    u32 fmemclk;
};

struct tag {
    struct tag_header hdr;
    union {
        struct tag_core        core;
        struct tag_mem32    mem;
        struct tag_videotext    videotext;
        struct tag_ramdisk    ramdisk;
        struct tag_initrd    initrd;
        struct tag_serialnr    serialnr;
        struct tag_revision    revision;
        struct tag_videolfb    videolfb;
        struct tag_cmdline    cmdline;

        /*
         * Acorn specific
         */
        struct tag_acorn    acorn;

        /*
         * DC21285 specific
         */
        struct tag_memclk    memclk;
    } u;
};

struct tagtable {
    u32 tag;
    int (*parse)(const struct tag *);
};

#define tag_member_present(tag,member)                \
    ((unsigned long)(&((struct tag *)0L)->member + )    \
        <= (tag)->hdr.size * )

#define tag_next(t)    ((struct tag *)((u32 *)(t) + (t)->hdr.size))
#define tag_size(type)    ((sizeof(struct tag_header) + sizeof(struct type)) >> 2)

#define for_each_tag(t,base)        \
    for (t = base; t->hdr.size; t = tag_next(t))

/*
 * Memory map description
 */
#define NR_BANKS 8

struct meminfo {
    int nr_banks;
    unsigned long end;
    struct {
        unsigned long start;
        unsigned long size;
        int           node;
    } bank[NR_BANKS];
};

extern struct meminfo meminfo;

#endif

6.Makefile

CC      = arm-linux-gcc
LD      = arm-linux-ld
AR      = arm-linux-ar
OBJCOPY = arm-linux-objcopy
OBJDUMP = arm-linux-objdump

CFLAGS         := -Wall -O2
CPPFLAGS       := -nostdinc -  -fno-builtin

objs := start.o init.o boot.o

boot.bin: $(objs)
    ${LD} -Tboot.lds -o boot.elf $^
    ${OBJCOPY} -O binary -S boot.elf $@
    ${OBJDUMP} -D -m arm boot.elf > boot.dis

%.o:%.c
    ${CC} $(CPPFLAGS) $(CFLAGS) -c -o $@ $<

%.o:%.S
    ${CC} $(CPPFLAGS) $(CFLAGS) -c -o $@ $<

clean:
    rm -f *.o *.bin *.elf *.dis