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