操作系统:ubuntu10.04
前言:
在上一章节中,分析了实现的思路。下面就是实现的源码,在源码中有详细的注释。
1,start.S
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/* watch dog registers */
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#define WTCON 0x53000000
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/* clock register */
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#define CLKDIVN 0x4C000014
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#define MPLLCON 0x4C000004
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#define S3C2440_MPLL_200MHZ ((0x5c<<12)|(0x01<<4)|(0x02))
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#define S3C2440_MPLL_400MHZ ((0x5c<<12)|(0x01<<4)|(0x01))
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/* sdram */
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#define MEM_CTL_BASE 0x48000000
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.text
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.global _start
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_start:
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/* 1. 关闭看门狗 */
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ldr r0, =WTCON
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mov r1, #0
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str r1, [r0]
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/* 2. 设置时钟 */
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ldr r0, =CLKDIVN
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//mov r1, #0x03; // FCLK:HCLK:PCLK=1:2:4, HDIVN=1,PDIVN=1
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mov r1, #0x05; // FCLK:HCLK:PCLK=1:4:8
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str r1, [r0]
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/* 如果HDIVN非0,CPU的总线模式应该从“fast bus mode”变为“asynchronous bus mode” */
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mrc p15, 0, r1, c1, c0, 0 /* 读出控制寄存器 */
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orr r1, r1, #0xc0000000 /* 设置为“asynchronous bus mode” */
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mcr p15, 0, r1, c1, c0, 0 /* 写入控制寄存器 */
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/* MPLLCON = S3C2440_MPLL_200MHZ */
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ldr r0, =MPLLCON
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//ldr r1, =S3C2440_MPLL_200MHZ
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ldr r1, =S3C2440_MPLL_400MHZ
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str r1, [r0]
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/* 启动ICACHE */
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mrc p15, 0, r0, c1, c0, 0 @ read control reg
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orr r0, r0, #(1<<12)
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mcr p15, 0, r0, c1, c0, 0 @ write it back
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/* 3. 初始化 SDRAM */
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ldr r0, =MEM_CTL_BASE
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adr r1, sdram_config
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add r3, r0, #(13*4)
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1:
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ldr r2, [r1], #4
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str r2, [r0], #4
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cmp r0, r3
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bne 1b
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/* 4. 重定位:把 bootloader 本身的代码从flash中复制到对应的内存的链接地址中*/
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ldr sp, =0x34000000 /* 64M SDRAM ,设置栈指针,栈是向下生长,故指向邋邋錝DRAM的最高处*/
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bl nand_init /* 初始化 NAND FLASH */
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mov r0, #0 /* src执行0地址。当为NAND FLASH 启动时,src指向的是邋錍PU片内内存的地址0.
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当 NOR FLASH 启动时,src指向的是NOR FLASH 的地址0*/
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ldr r1, =_start /* dest地址,为 *.lds 中定义的起始地址,此处为 0x33f80000*/
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ldr r2, =__bss_start /* bss 段的起始地址*/
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sub r2, r2, r1 /* r2 - r1,表示这个*.bin 文件的大小*/
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bl copy_code_to_sdram
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bl clear_bss /* 清空 sdram 中 *.bin文件的bss段内存地址*/
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/* 5. 跳转到第二部分代码中执行*/
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ldr lr, =halt /* 当 main 函数返回时,执行 halt 代码*/
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ldr pc, =main
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halt: /* 死循环 */
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b halt
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sdram_config:
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.long 0x22011110 //BWSCON
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.long 0x00000700 //BANKCON0
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.long 0x00000700 //BANKCON1
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.long 0x00000700 //BANKCON2
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.long 0x00000700 //BANKCON3
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.long 0x00000700 //BANKCON4
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.long 0x00000700 //BANKCON5
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.long 0x00018005 //BANKCON6
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.long 0x00018005 //BANKCON7
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.long 0x008C04F4 // REFRESH
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.long 0x000000B1 //BANKSIZE
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.long 0x00000030 //MRSRB6
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.long 0x00000030 //MRSRB7
2,boot.lds
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SECTIONS {
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. = 0x33f80000;
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.text : { *(.text) }
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. = ALIGN(4);
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.rodata : {*(.rodata)}
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. = ALIGN(4);
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.data : { *(.data) }
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. = ALIGN(4);
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__bss_start = .;
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.bss : { *(.bss) *(COMMON) }
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__bss_end = .;
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}
3,init.c
点击(此处)折叠或打开
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/* nand flash */
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#define NFCONF (*((volatile unsigned long *)0x4E000000))
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#define NFCONT (*((volatile unsigned long *)0x4E000004))
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#define NFCMMD (*((volatile unsigned char *)0x4E000008))
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#define NFADDR (*((volatile unsigned char *)0x4E00000C))
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#define NFDATA (*((volatile unsigned char *)0x4E000010))
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#define NFSTAT (*((volatile unsigned char *)0x4E000020))
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/* gpio */
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#define GPHCON (*((volatile unsigned long *)0x56000070))
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#define GPHUP (*((volatile unsigned long *)0x56000078))
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/* uart registers*/
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#define ULCON0 (*((volatile unsigned long *)0x50000000))
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#define UCON0 (*((volatile unsigned long *)0x50000004))
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#define UFCON0 (*((volatile unsigned long *)0x50000008))
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#define UMCON0 (*((volatile unsigned long *)0x5000000c))
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#define UTRSTAT0 (*((volatile unsigned long *)0x50000010))
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#define UTXH0 (*((volatile unsigned long *)0x50000020))
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#define URXH0 (*((volatile unsigned long *)0x50000024))
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#define UBRDIV0 (*((volatile unsigned long *)0x50000028))
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void nand_read(unsigned int addr, unsigned char *buf, unsigned int len);
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void nand_addr(unsigned int addr);
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void nand_init(void)
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{
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#define TACLS 0
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#define TWRPH0 1
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#define TWRPH1 0
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/* 设置时钟*/
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NFCONF = (TACLS<<12) | (TWRPH0<<8) | (TWRPH1<<4) ;
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/* 使能NAND FLASH 控制器,初始化ECC,禁止片选*/
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NFCONT = (1<<4) | (1<<1) | (1<<0);
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}
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static void nand_select(void)
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{
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NFCONT &= ~(1<<1);
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}
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static void nand_deselect(void)
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{
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NFCONT |= (1<<1);
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}
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static void nand_cmd(unsigned char cmd)
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{
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volatile char i = 0;
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NFCMMD = cmd;
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for( i = 0; i < 10; i++) ; /* 稍微延时,确保命令正确写入*/
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}
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static void nand_wait_ready(void)
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{
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while(!(NFSTAT & 0x01)) ;
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}
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static unsigned char nand_data(void)
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{
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return NFDATA;
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}
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void nand_addr(unsigned int addr)
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{
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unsigned int col = addr % 2048;
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unsigned int page = addr / 2048;
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volatile int i;
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/* 写一个地址,需要分成五个步骤*/
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/* 先写入两个列地址*/
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NFADDR = col & 0xff;
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for (i = 0; i < 10; i++);
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NFADDR = (col >> 8) & 0xff;
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for (i = 0; i < 10; i++);
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NFADDR = page & 0xff;
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for (i = 0; i < 10; i++);
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NFADDR = (page >> 8) & 0xff;
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for (i = 0; i < 10; i++);
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NFADDR = (page >> 16) & 0xff;
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for (i = 0; i < 10; i++);
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}
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void nand_read(unsigned int addr, unsigned char * buffer,unsigned int len)
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{
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int col = addr % 2048;
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int i = 0;
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/* 1 选中*/
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nand_select();
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while(i < len)
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{
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/* 2 发出读命令00h */
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nand_cmd(0x00);
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/* 3 发出地址(分5 步发出) */
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nand_addr(addr);
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/* 4 发出读命令30h */
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nand_cmd(0x30);
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/* 5 判断状态*/
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nand_wait_ready();
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/* 6 读数据*/
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/* 当前NAND FLASH 是以2k为一页的*/
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/* 每次读取一页数据到对应寄存器中*/
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for( ; (col < 2048) && ( i < len) ; col++ )
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{
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buffer[i] = nand_data();
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i++;
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addr++;
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}
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col = 0; /* 如果数据分布在不同的页中,则读取下一页时,从第0列开始读取*/
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}
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/* 7 取消选中*/
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nand_deselect();
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}
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#if 1
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int isBootFromNorFlash(void)
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{
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volatile int *p = (volatile int*)0;
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int val = 0;
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val = *p;
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*p = 0x12345678; /* Nor Flash 中是不允许写入数据的*/
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if(0x12345678 == *p)
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{
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/* 写成功,是NAND FLASH */
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*p = val;
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return 0;
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}
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else
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{
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/* NOR FLASH 不能像内存一样写*/
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return 1;
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}
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}
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void copy_code_to_sdram(unsigned char *src, unsigned char *dest, unsigned int len)
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{
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int i = 0;
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if(isBootFromNorFlash())
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{
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/* NOR FLASH 中的数据可以像内存中的数据那样,直接读取*/
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while( i < len )
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{
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dest[i] = src[i];
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i++;
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}
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}
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else
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{
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/* NAND FLASH*/
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nand_read((unsigned int )src, dest, len);
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}
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}
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#endif
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void clear_bss(void)
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{
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extern int __bss_start,__bss_end;
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int *p = &__bss_start;
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for( ; p < &__bss_end; p++)
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*p = 0;
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}
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#define PCLK 50000000 /* start.S 中把时钟设置PCLK为50MHz*/
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#define UART_CLK PCLK /* UART0的时钟源设为PCLK */
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#define UART_BAUD_RATE 115200 /* 波特率为115200*/
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#define UART_BRD ((UART_CLK / (UART_BAUD_RATE * 16)) - 1)
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void uart0_init(void)
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{
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GPHCON |= 0xa0; /* GPH2,GPH3用作TXD0,RXD0 */
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GPHUP = 0x0C; /* GPH2,GPH3 内部上拉*/
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ULCON0 = 0x03; /* 8N1(8个数据位,无较验,1个停止位) */
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UCON0 = 0x05; /* 查询方式,UART时钟源为PCLK */
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UFCON0 = 0x00; /* 不使用FIFO */
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UMCON0 = 0x00; /* 不使用流控制*/
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UBRDIV0 = UART_BRD; /* 波特率为115200 */
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}
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#define TXD0READY (1<<2)
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void putc(unsigned char c)
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{
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/* 等待,直到发送缓冲区中的数据已经全部发送出去 */
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while(!(UTRSTAT0 & TXD0READY)) ;
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/* 向UTXH0寄存器中写入数据,UART即自动将它发送出去 */
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UTXH0 = c;
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}
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void puts(char * str)
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{
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int i = 0;
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while(str[i])
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{
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putc(str[i]);
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++i;
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}
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}
4,boot.c
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#include "setup.h"
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extern void uart0_init(void);
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extern void nand_read(unsigned int addr, unsigned char * buffer,unsigned int len);
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extern void puts(char * str);
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int strlen(char *str)
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{
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int i = 0;
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while (str[i])
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{
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i++;
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}
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return i;
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}
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void strcpy(char *dest, char *src)
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{
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while ((*dest++ = *src++) != '\0');
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}
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static struct tag *params;
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void setup_start_tag(void)
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{
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params = (struct tag *)0x30000100; /* 内核约定存放在这个地方*/
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params->hdr.tag = ATAG_CORE;
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params->hdr.size = tag_size (tag_core);
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params->u.core.flags = 0;
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params->u.core.pagesize = 0;
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params->u.core.rootdev = 0;
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params = tag_next (params);
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}
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void setup_memory_tags(void)
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{
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params->hdr.tag = ATAG_MEM;
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params->hdr.size = tag_size (tag_mem32);
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params->u.mem.start = 0x30000000; /* SDRAM起始地址*/
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params->u.mem.size = 64*1024*1024; /* 其大小为64 M */
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params = tag_next (params);
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}
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void setup_commandline_tag(char *cmdline)
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{
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int len = strlen(cmdline) + 1;
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params->hdr.tag = ATAG_CMDLINE;
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/* 以4 个字节对齐,并且以4个字节为单位*/
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params->hdr.size = (sizeof (struct tag_header) + len + 3) >> 2;
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strcpy (params->u.cmdline.cmdline, cmdline);
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params = tag_next (params);
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}
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void setup_end_tag(void)
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{
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params->hdr.tag = ATAG_NONE;
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params->hdr.size = 0;
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}
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int main(void)
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{
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/* 函数指针,执行内核的起始位置*/
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void (*theKernel)(int zero, int arch, unsigned int params);
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/* 1 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*/
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uart0_init();
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/* 2 从NAND FLASH 中把内核读入到内存中*/
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puts("Copy kernel from nand\n\r");
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/* 内核存放在NAND FLASH 中的0x60000 地址。
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存放的是uImage,该文件包含64 字节的头部信息。
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内核一般都存放在0x30008000这个地址,除非手动修改内核。*/
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nand_read(0x60000+64,( unsigned char * )0x30008000, 0x200000);
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/* 3 设置引导内核的参数*/
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puts("Set boot params\n\r");
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setup_start_tag();
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setup_memory_tags(); /*内核大小*/
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setup_commandline_tag("noinitrd root=/dev/mtdblock3 init=/linuxrc console=ttySAC0"); /* 命令参数*/
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setup_end_tag();
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/* 4 跳转执行*/
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puts("Boot kernel\n\r");
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theKernel = (void (*)(int ,int ,unsigned int))0x30008000; /* 真正的内核起始地址*/
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/* 参数1 : 默认为0.
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参数2 : 为machine ID,当前设置为362。可在内核源码中: arch/arm/tools/mach_types 修改。
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参数3 : 为参数的起始地址(params)*/
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theKernel(0,362,0x30000100);
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/* 5 异常:如果正确引导内核,不应该执行到这里*/
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puts("Error!\n\r");
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return -1;
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}
5,setup.h
该文件是直接从uboot中复制过来的。
6,Makefile
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CC = arm-linux-gcc
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LD = arm-linux-ld
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AR = arm-linux-ar
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OBJCOPY = arm-linux-objcopy
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OBJDUMP = arm-linux-objdump
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CFLAGS := -Wall -O2
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CPPFLAGS := -nostdinc -nostdlib -fno-builtin
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objs := start.o init.o boot.o
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boot.bin: $(objs)
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${LD} -Tboot.lds -o boot.elf $^
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${OBJCOPY} -O binary -S boot.elf $@
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${OBJDUMP} -D -m arm boot.elf > boot.dis
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%.o:%.c
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${CC} $(CPPFLAGS) $(CFLAGS) -c -o $@ $<
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%.o:%.S
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${CC} $(CPPFLAGS) $(CFLAGS) -c -o $@ $<
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clean:
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rm -f *.o *.bin *.elf *.dis
7,总结
至此,从零开始实现的uboot基本完成。
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