關於S3C2440的啟動方式有兩種：Nor Flash 啟動和Nand Flash 啟動。
Nor Flash 和Nand Flash 都是非易失性記憶體，Nor Flash 的特點是晶片內執行和不能直接寫操作，程式可以直接在其中運行，而不必將程式讀取到RAM 中運行。Nor Flash 雖然具有這個優點，但是它的性價比遠低於Nand Flash，因而很多系統採用Nand Flash 啟動。Nand Flash 的特點是採用非線性存儲模式，程式無法在其中運行，它只能作為程式或資料的存儲載體，存儲在其中的程式只能先拷貝到RAM 中才能運行。
從Nor Flash 啟動時，與nGCS0 相連的Nor Flash 就被映射到nGCS0 片選的空間，其位址被映射為0x00000000；從Nand Flash 啟動時，S3C2440 晶片內部自帶的一塊容量為4K 的被稱為“Steppingstone”的BootSRAM 被映射到nGCS0 片選的空間，其位址被映射為0x00000000。當系統上電或重定時，程式會從0 位址處開始執行，因此我們編寫的啟動代碼要確保存儲在0 位址處。
當啟動方式為Nor Flash 啟動時，沒有額外需要考慮的問題，因為這種情況下程式在系統啟動前就存儲在Nor Flash 中，我們只要保證將啟動代碼保存在Nor Flash 開始的位置即可，系統上電或重定時，0 位址處的啟動代碼就會被執行。
在啟動方式為Nand Flash 啟動的情況下，系統啟動前所有的程式存儲在Nand Flash 中，系統的啟動過程稍微有點複雜：系統上電或重定時，0 位址處為S3C2440 內部自帶的BootSRAM，啟動前裡面沒有任何存儲內容，啟動後S3C2440 先通過硬體機制將Nand Flash 前4K 的內容拷貝至其中，然後再運行裡面的程式（從0 位址處）。這種情況下我們需要保證將啟動代碼保存在Nand Flash 開始的位置，並且啟動代碼的大小要小於4K。這就是我們的裸機程式為什麼在nandflash能跑的原因。
 |
| 啟動流程 |
系統上電之後，需要一段程式來進行初始化。比如：關閉WATCHDOG、改變系統時鐘(system clock controller)、初始化記憶體控制器(memory controller)、將更多的代碼複製到記憶體中(SDRAM)等。如果它能將作業系統內核覆制到記憶體中運行，無論從本地（比如Flash）還是從遠端（比如通過網路），就稱這段程式為Bootloader。簡單地說，Bootloader就是那麼一小段程式，它在系統上電時開始執行，，初始化硬體設備、準備好軟體環境，最後調用作業系統內核。
啟動過程: 系統上電 --> Bootloader --> Kernel --> Filesystem --> Application
Bootloader 可視作裸機程式集合，在系統上電時，需做硬體初始化，使得作業系統能夠在系統上運行，其主要重點如下
- 對硬體的操作
- 對ARM處理器的瞭解
- 程式的基本概念：重定位、棧、程式碼片段、資料段、BSS段
自己寫 Bootloader 程式流程:
- close watchdog
- set system clock
- initail sdram
- relocate location, 把bootloader本身的代碼從flash複製到它的連結位址去
- run main
- 從NAND FLASH 把內核讀入內存
- 設置參數(放置Kernel所需要的參數)
- 跳轉執行
 |
| params |
====================================
start.c
#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 ● close watchdog
ldr r0, =0x5300000
mov r1, #0
str r1, [r0]
//2 ● set system clock
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, HDIVN=2,PDIVN=1
str r1, [r0]
// s3c2440 規定
// 如果HDIVN非0，CPU的匯流排模式應該從“fast bus mode”變為“asynchronous
bus mode”
mrc p15, 0, r1, c1, c0, 0 /* 讀出控制暫存器 */
orr r1, r1, #0xc0000000 /* 設置為“asynchronous bus mode” */
mcr p15, 0, r1, c1, c0, 0 /* 寫入控制暫存器*/
// MPLLCON = S3C2440_MPLL_200MHZ
ldr r0, =0x4c000004
// ldr r1, = S3C2440_MPLL_200MHZ
ldr r1, = S3C2440_MPLL_400MHZ
str r1, [r0]
// 啟動ICACHE
mrc p15, 0, r0, c1, c0, 0 @ read control reg
orr r0, r0, #(1<<12)
mcr p15, 0, r0, c1, c0, 0 @ write it back
//3 ● initail sdram
ldr r0, =MEM_CTL_BASE
adr r1, sdram_config
add r3, r0, #(13*4)
1:
ldr r2, [r1], #4
str r2, [r0], #4
cmp r0, r3
bne 1b @f:往前跳
//4 ● relocate location, 把bootloader本身的代碼從flash複製到它的連結位址去
ldr sp, =0x34000000
bl copy_code_to_sdram
mov r0, #0
ldr r1, =_start
ldr r2, =__bss_start
sub r2, r2, r1
bl copy_code_to_sdram
bl clear_bss
//5 ● run 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
====================================
boot.c
#include "setup.h"
void setup_start_tag(void);
void setup_memory_tags(void);
void setup_commandline_tag(char *cmdline);
void setup_end_tag(void);
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);
int main(void)
{
void (*theKernel)(int zero, int arch, unsigned int params);
volatile unsigned int *p = (volatile unsigned int *)0x30008000;
// 0. 幫內核設置串口: 內核啟動的開始部分會從串口列印一些資訊,
// 但是內核一開始沒有初始化串口
// 若不初始化串口，程式會變成死循環
uart0_init();
// 1. 從NAND FLASH 把內核讀入內存
puts("Copy kernel from nand\n\r");
nand_read(0x60000 + 64, (unsigned char *)0x30008000, 0x200000);
puthex(0x12345ABCD);
puts("\n\r");
puthex(*p);
puts("\n\r");
// 2.設置參數
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. 跳轉執行
puts("Boot kernel\n\r");
theKernel = (void (*)(int, int, unsigned int))0x30008000;
theKernel(0, 362, 0x30000100);
/*
* mov r0, #0
* ldr r1, =362
* ldr r2, =0x30000100
* mov pc, #0x30008000
*/
// 如果一切正常, 不會執行到這裡
puts("Error!\n\r");
return -1;
}
static struct tag *params; // 設置kernel所需參數
void setup_start_tag(void)
{
params = (struct tag*)0x30000100;
params -> hdr.tag = ATAG_CORE;
params -> hdr.size = tag_size(tag_core);
params -> u.core.flags = 0;
params -> u.core.pagesize = 0;
params -> u.core.rootdev = 0;
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; // bd->bi_dram[i].start;
params->u.mem.size = 64*1024*1024; // (64*1024*1024 = 0x4000000)
// bd->bi_dram[i].size;
// bd->bi_dram[i].size;
params = tag_next (params);
}
int strlen(char *str)
{
int i = 0;
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) + 1;
params->hdr.tag = ATAG_CMDLINE;
params->hdr.size = (sizeof (struct tag_header) + len + 3) >> 2;
strcpy (params->u.cmdline.cmdline, cmdline);
params = tag_next (params);
}
void setup_end_tag(void)
{
params->hdr.tag = ATAG_NONE;
params->hdr.size = 0;
}
====================================
init.c
// NAND FLASH Controller
#define NFCONF (*(volatile unsigned long *)0x4E000000)
#define NFCONT (*(volatile unsigned long *)0x4E000004)
#define NFCMMD (*(volatile unsigned long *)0x4E000008)
#define NFADDR (*(volatile unsigned long *)0x4E00000C)
#define NFDATA (*(volatile unsigned long *)0x4E000010)
#define NFSTAT (*(volatile unsigned long *)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);
void nand_select(void);
void nand_deselect(void);
void nand_cmd(unsigned char cmd);
void nand_addr(unsigned int addr);
void nand_wait_ready(void);
unsigned char nand_data(void);
void nand_select(void);
void nand_deselect(void);
void nand_cmd(unsigned char cmd);
void nand_addr(unsigned int addr);
void nand_wait_ready(void);
unsigned char nand_data(void);
int isBootFromNorFlash(void)
{
volatile int *p = (volatile *)0;
int val;
val = *p;
*p = 0x12345678;
if(*p == 0x12345678)
{
// 寫成功，nand啟動
*p = val;
return 0;
}
else
{
// NOR不能像內存一樣寫
return 1;
}
}
void copy_code_to_sdram(unsigned char *src, unsigned char *dest, unsigned int len)
{
// NOR Start
if(isBootFromNorFlash())
{
while(i < len)
{
dest[i] = src[i];
i++;
}
}
else
{
// nand_init(); 放到start.s, 因為不管是nor啟動或是nand啟動，同樣需要將
// 內核從nand複製到sdram
nand_read(src, dest, len);
}
}
void clear_bss()
{
extern int __bss_state, __bss_end;
int *p = &__bss_state;
for(;p < &__bss_end; p++)
{
*p = 0;
}
}
void nand_init(void)
{
#define TACLS 0
#define TWRPH0 1
#define TWRPH1 0
// 設置時序
NFCONF = (TACLS << 12) | (TWRPH0 << 8) | (TWRPH1 << 4);
// 始能NAND FLASH Controller, 初始化ECC, 禁止片選
NFCONT = (1 << 4) | (1 << 1) | (1 << 0);
}
void nand_read(unsigned int addr, unsigned char *buffer, unsigned int len)
{
int col = addr % 2048; // 可能從中間page開始讀
int i = 0;
// 1. 選中
nand_select();
while(i < len)
{
// 2. 發出read命令 (00h)
nand_cmd(0x00);
// 3. 發出地址(分五次發出)
nand_addr(addr);
// 4. 發出read命命 (0x3h)
nand_cmd(0x03);
// 5. 判斷狀態
nand_wait_ready();
// 6. read 數據
for(; (col < 2048) && (i < len); col++)
{
buf[i] = nand_data();
i++;
addr++;
}
col = 0; // 讀完一頁, col 歸零
}
// 7. 取消選中
nand_deselect();
}
void nand_select(void)
{
NFCONT &= ~(1<<1);
}
void nand_deselect(void)
{
NFCONT |= (1<<1);
}
void nand_cmd(unsigned char cmd)
{
volatile int i;
NFCMMD = cmd;
for (i = 0; i < 10; i++);
}
void nand_addr(unsigned int addr)
{
unsigned int col = addr % 2048;
unsigned int page = addr / 2048;
unsigned int i;
NFADDR = col & 0xff;
for (i = 0; i < 10; i++);
NFADDR = (col >> 8) && 0xff;
for (i = 0; i < 10; i++);
NFADDR = page & 0xff;
for (i = 0; i < 10; i++);
NFADDR = (page >> 8) & 0xff;
for (i = 0; i < 10; i++);
NFADDR = (page >> 16) & 0xff;
for (i = 0; i < 10; i++);
}
void nand_wait_ready(void)
{
while(!(NFSTAT & 1));
}
unsigned char nand_data(void)
{
return NFDATA;
}
#define PCLK 50000000 // init.c中的clock_init函數設置PCLK為50MHz
#define UART_CLK PCLK // UART0的時鐘源設為PCLK
#define UART_BAUD_RATE 115200 // 串列傳輸速率
#define UART_BRD ((UART_CLK / (UART_BAUD_RATE * 16)) - 1)
/*
* 初始化UART0
* 115200,8N1,無流控
*/
void uart0_init(void)
{
GPHCON |= 0xa0; // GPH2,GPH3用作TXD0,RXD0
GPHUP = 0x0c; // GPH2,GPH3內部上拉
ULCON0 = 0x03; // 8N1(8個資料位元，無較驗，1個停止位)
UCON0 = 0x05; // 查詢方式，UART時鐘源為PCLK
UFCON0 = 0x00; // 不使用FIFO
UMCON0 = 0x00; // 不使用流控
UBRDIV0 = UART_BRD; // 串列傳輸速率為115200
}
// 發送一個字元
void putc(unsigned char c)
{
// 等待，直到發送緩衝區中的資料已經全部發送出去
while (!(UTRSTAT0 & TXD0READY));
// 向UTXH0寄存器中寫入資料，UART即自動將它發送出去
UTXH0 = c;
}
// 打印除錯訊息
void puts(char *str)
{
int i = 0;
while(str[i])
{
putc(str[i]);
i++;
}
}
void puthex(unsigned int val)
{
// 0x1234abcd
int i,j;
puts("0x");
for(i=0; i<8; i++)
{
j = (val >> ((7-i)*4)) & 0xf;
if((j >= 0) && (j <= 9))
putc('0' + j);
else
putc('A' + j - 0xa);
}
}
====================================
/*
* 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[4]; /* 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[256];
} u1;
union {
char paths[8][128];
struct {
unsigned long magic;
char n[1024 - 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[1]; /* 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 + 1) \
<= (tag)->hdr.size * 4)
#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
====================================
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 -nostdlib -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
====================================
boot.lds
SECTIONS {
. = 0x33f80000;
.text : { *(.text) }
. = ALIGN(4);
.rodata : {*(.rodata*)}
. = ALIGN(4);
.data : { *(.data) }
. = ALIGN(4);
__bss_start = .;
.bss : { *(.bss) *(COMMON) }
__bss_end = .;
}
. = 0x33f80000;
.text : { *(.text) }
. = ALIGN(4);
.rodata : {*(.rodata*)}
. = ALIGN(4);
.data : { *(.data) }
. = ALIGN(4);
__bss_start = .;
.bss : { *(.bss) *(COMMON) }
__bss_end = .;
}
====================================
- 嵌入式Linux應用開發完全手冊
- S3C2440手冊
- http://6xudonghai.blog.163.com/blog/static/336406292008724103317304/ (arm9的CP15 && MRC && MCR)
- http://blog.csdn.net/tommy_wxie/article/details/8847247 (Uboot分析)
- http://blog.csdn.net/tommy_wxie/article/details/8760770 (Boot Loader啟動過程分析)
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