UBoot支持双启动(Nor and Nand)及环境变量保存的实现

本文所要讲述的是如何使UBoot只编译一次就能支持从Nor Flash和Nand Flash启动,并且在保存环境变量时能够保存在其所在的Flash中.


注意,本文针对的为S3C2410芯片,其他芯片原理相同,可在适当修改代码后进行移植.


我们知道UBoot源码本身直接支持从Nor Flash启动,这是Nor Flash的可执行特性决定的.而针对Nand Flash,则涉及到前4K数据的问题.S3C2410的Nand Flash控制器有一个特殊的功能,就是能在上电后自动将Nand Flash中的前4K数据搬移到4K内部的RAM中,并把0x00000000设置为内部RAM的起始地址,然后CPU从内部RAM的0x000000位置启动,该过程由硬件自动完成.
所以,要使UBoot支持从Nand Flash启动,必须在其前4K代码执行过程中完成将自身复制到RAM中的工作.

但是,我们现在需要让UBoot支持双启动,现在的问题就是该如何判断UBoot是在Nor Flash还是在Nand Flash中呢?呵呵,在S3C2410(S3C2440)中,这个可以通过BWSCON(BUS WIDTH & WAIT CONTROL REGISTER)控制寄存器[2:1]的值进行判断,如果为00则表示是从Nand Flash启动的.因此,我们可以直接通过如下代码进行判断并在BWSCON[2:1]为00时跳转到UBoot复制自身(copy_myself)的代码处:

#define	BWSCON		0x48000000
	ldr		r0, =BWSCON
	ldr 	r0, [r0]
	ands 	r0, r0, #6		@ 判断BWSCON[2:1]是否为00,如果是,则跳转到copy_myself
	beq		copy_myself

好了,双启动问题算是解决了,但是新的问题又来了,这个环境变量又应该如何保存呢?是都保存到Nor Flash还是Nand Flash呢?当然,最好的方式还是保存到各自所在的Flash中.这个可以设置一个标志,在进入Nand Flash启动代码时设置该标志,表示从Nand Flash启动,然后,在保存环境变量时通过该标志的值判断是调用Nor Flash的保存方法还是Nand Flash的保存方法.


下面讲解具体的修改过程(以u-boot-2010.09为例).
首先,修改include/configs/smdk2410.h文件,添加如下宏定义:

#define CONFIG_CMD_ENV	// 开启环境变量操作命令
#define CONFIG_CMD_NAND	// 开启Nand Flash操作命令
#ifdef CONFIG_CMD_NAND
#	define CONFIG_SYS_NAND_BASE            0x4E000000 //Nand配置寄存器基地址
#	define CONFIG_SYS_MAX_NAND_DEVICE      1
#	define CONFIG_MTD_NAND_VERIFY_WRITE    1

#	define CONFIG_NAND_S3C2410
#	define STACK_BASE 0x33f00000   /* 堆栈基址 */
#	define STACK_SIZE 0x8000       /* 堆栈大小 */
#endif

/*---------------------------------------------------------------------
 * Boot From Nor or Nand Flash or both
 */
#define CONFIG_NOR_BOOT
#define CONFIG_NAND_BOOT

#ifdef CONFIG_NOR_BOOT
#	define PHYS_FLASH_1		0x00000000 /* Flash Bank #1 */
#	define CONFIG_SYS_FLASH_BASE		PHYS_FLASH_1

#	define CONFIG_AMD_LV160B	/* 使用AM29LV160DB Nor Flash芯片 */

#	define CONFIG_SYS_MAX_FLASH_BANKS	1	/* max number of memory banks */

/* timeout values are in ticks */
#	define CONFIG_SYS_FLASH_ERASE_TOUT	(5*CONFIG_SYS_HZ) /* Timeout for Flash Erase */
#	define CONFIG_SYS_FLASH_WRITE_TOUT	(5*CONFIG_SYS_HZ) /* Timeout for Flash Write */

#	define	CONFIG_ENV_IS_IN_FLASH	/* 将环境变量保存到Nor Flash中*/
#endif

#ifdef CONFIG_NAND_BOOT
#	define UBOOT_RAM_BASE		0x33f80000
#	define NAND_CTL_BASE		0x4E000000
#	define bINT_CTL(Nb)		__REG(INT_CTL_BASK + (Nb))
#	define oNFCONF			0x00
#	define oNFCMD			0x04
#	define oNFADDR			0x08
#	define oNFDATA			0x0c
#	define oNFSTAT			0x10
#	define oNFECC			0x14

#	define CONFIG_UBOOT_SIZE		0x30000
#	define CONFIG_ENV_IS_IN_NAND	/* common/env_nand.c */

#	ifndef CONFIG_NOR_BOOT
#		define CONFIG_SYS_NO_FLASH
#		undef CONFIG_CMD_FLASH
#		undef CONFIG_CMD_IMLS
#	endif
#endif

/*---------------------------------------------------------------------------
 * Nor Flash Device
 */
#ifdef CONFIG_AMD_LV160B
#	define PHYS_FLASH_SIZE		0x00200000	/* 2MB */
#	define CONFIG_SYS_MAX_FLASH_SECT	(35)	/* max number of sectors on one chip */
#	define CONFIG_ENV_ADDR		(CONFIG_SYS_FLASH_BASE + 0x030000)/* addr of environment */
#endif

/*--------------------------------------------------------------------------
 * Environment Setting
 */
// 环境变量的大小必须为sector的整数倍,此处直接设置为0x1000,
// 能够同时满足Nor Flash和Nand Flash的要求
#define	CONFIG_ENV_SIZE		0x10000
#ifdef	CONFIG_ENV_IS_IN_FLASH
//#	define	CONFIG_ENV_ADDR  (CONFIG_SYS_FLASH_BASE + 0x30000)
#endif
#ifdef	CONFIG_ENV_IS_IN_NAND
#	define	CONFIG_ENV_OFFSET	CONFIG_UBOOT_SIZE /* 环境变量紧接在uboot之后 */
#endif

然后,修改启动文件arch/arm/cpu/arm920t/start.S,增加Nand Flash启动代码和启动标志的设置(直接修改relocate代码段):

/* 双启动判断 */
#define	BWSCON		0x48000000
	ldr		r0, =BWSCON
	ldr 	r0, [r0]
	ands 	r0, r0, #6		@ 判断BWSCON[2:1]是否为00,如果是,则跳转到copy_myself
	beq		copy_myself

#ifdef CONFIG_NOR_BOOT
#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
	
	b stack_setup		/* 跳过nand启动代码 */
#endif	/* CONFIG_SKIP_RELOCATE_UBOOT */
#endif  /* CONFIG_NOR_BOOT */

#ifdef	CONFIG_NAND_BOOT
copy_myself:       
	@ reset NAND
	mov r1, #NAND_CTL_BASE
	ldr r2, =0xf830           	@ initial value
	str r2, [r1, #oNFCONF]
	ldr r2, [r1, #oNFCONF]
	bic r2, r2, #0x800          @ enable chip
	str r2, [r1, #oNFCONF]
	mov r2, #0xff		    @ RESET command
	strb r2, [r1, #oNFCMD]
	mov r3, #0                  @ wait

nand1: 
	add	r3, r3, #0x1
	cmp	r3, #0xa
	blt nand1

nand2:
	ldr r2, [r1, #oNFSTAT]      @ wait ready
	tst r2, #0x1
	beq nand2

	ldr r2, [r1, #oNFCONF]
	orr r2, r2, #0x800          @ disable chip
	str r2, [r1, #oNFCONF]

	@ get read to call C functions (for nand_read())
	ldr sp, DW_STACK_START      @ setup stack pointer
	mov fp, #0                  @ no previous frame, so fp=0

	@ copy U-Boot to RAM
	ldr r0, =UBOOT_RAM_BASE		@ buf : first parameter of nand_read_ll()
	mov r1, #0x0			@ start_addr : second parameter of nand_read_ll()
	mov r2, #CONFIG_UBOOT_SIZE	@ size : third parameter of nand_read_ll()
	bl  nand_read_ll
	tst r0, #0x0
	beq ok_nand_read

bad_nand_read:
	loop2:  b     loop2          	@ infinite loop

ok_nand_read:
	@ set flag : 0->boot from nand;1->boot from nor
	@ set flag after finishing to copy U-Boot to memory
	ldr	r0, =boot_flash		@ defined in common/cmd_nvedit.c
    mov	r1, #0x0
    str	r1, [r0]
	
	@ verify
	mov r0, #0
	ldr r1, =UBOOT_RAM_BASE		@ NOTE: DON'T USE '_TEXT_BASE'
	mov r2, #0x400     		@ 4 bytes * 1024 = 4K-bytes

go_next:
	ldr r3, [r0], #4
	ldr r4, [r1], #4
	teq r3, r4
	bne notmatch
	subs r2, r2, #4
	beq  stack_setup
	bne  go_next

notmatch:
	loop3:  b     loop3         @ infinite loop
#endif	/* CONFIG_NAND_BOOT */
	.align 2
DW_STACK_START: .word STACK_BASE+STACK_SIZE-4

其中,boot_flash为1表示从Nor Flash启动,为0则表示从Nand Flash启动,为使该值能够正确被修改,所以将其在UBoot复制完毕后进行修改.代码中的UBOOT_RAM_BASE不要直接替换为_TEXT_BASE,虽然两者值相同,但是在运行中却有问题,我就因为使用了_TEXT_BASE,导致费了很多时间,前车之荐,请勿效仿!
nand_read_ll为新增加的Nand Flash读取方法,在board/samsung/smdk2410目录下新建文件nand_read.c,并添加如下代码:

#include <config.h>
#define __REGb(x) (*(volatile unsigned char *)(x))
#define __REGi(x) (*(volatile unsigned int *)(x))
#define NF_BASE   0x4e000000
#define NFCONF    __REGi(NF_BASE + 0x0)
#define NFCMD     __REGb(NF_BASE + 0x4)
#define NFADDR    __REGb(NF_BASE + 0x8)
#define NFDATA    __REGb(NF_BASE + 0xc)
#define NFSTAT    __REGb(NF_BASE + 0x10)

#define BUSY 1
inline void wait_idle(void) {
    int i;

    while(!(NFSTAT & BUSY))
        for(i=0; i<10; i++);
}

#define NAND_SECTOR_SIZE 512
#define NAND_BLOCK_MASK   (NAND_SECTOR_SIZE - 1)

/* low level nand read function */
int nand_read_ll(unsigned char *buf, 
                unsigned long start_addr, 
                int            size)
{
    int i, j;

    if ((start_addr & NAND_BLOCK_MASK) || (size & NAND_BLOCK_MASK)) {
        return -1; /* invalid alignment */
    }

    /* chip Enable */
    NFCONF &= ~0x800;
    for(i=0; i<10; i++);

    for(i=start_addr; i < (start_addr + size);) {
        /* READ0 */
        NFCMD = 0;

        /* Write Address */
        NFADDR = i & 0xff;
        NFADDR = (i >> 9) & 0xff;
        NFADDR = (i >> 17) & 0xff;
        NFADDR = (i >> 25) & 0xff;

        wait_idle();

        for(j=0; j < NAND_SECTOR_SIZE; j++, i++) {
            *buf = (NFDATA & 0xff);
            buf++;
        }
    }

    /* chip Disable */
    NFCONF |= 0x800; /* chip disable */

    return 0;
}

修改Makefile,使nand_read.c能够被编译进UBoot:
COBJS := smdk2410.o flash.o nand_read.o
为了保证nand_read_ll方法能够被编译到UBoot代码的前4K中,以确保代码的正确执行,还需修改链接文件arch/arm/cpu/arm920t/u-boot.lds,如下:

.text :
	{
		arch/arm/cpu/arm920t/start.o	(.text)
		board/samsung/smdk2410/lowlevel_init.o	(.text)
		board/samsung/smdk2410/nand_read.o	(.text)
		*(.text)
	}

最后,该修改代码以支持环境变量的保存了.
在UBoot中,环境变量操作的命令在文件common/cmd_nvedit.c中定义和实现,而针对不同Flash的操作,如env_init,saveenv和env_relocate_spec,则在common/env_flash.c和common/env_nand.c中进行定义和实现.
为了双启动的支持,并且能够支持单启动(Nor或Nand启动),我们将上面三个方法整合到了cmd_nvedit.c中,并将env_flash.c和env_nand.c中的这三个方法添加上nor和nand前缀,用于区分调用,并防止同时编译时的重定义.
然后,将env_flash.c和env_nand.c中定义的env_name_spec和env_ptr两个变量放到cmd_nvedit.c中进行定义,这两个文件直接使用extern关键字引用这两个变量.由于函数env_get_char_spec在env_flash.c和env_nand.c中都进行了定义,所以也和env_init一样转到cmd_nvedit.c中进行定义.
接着,就是定义启动标志boot_flash,并设置初值为1.


具体修改如下:
在common/cmd_nvedit.c中增加如下代码:

// 1:NOR FLASH启动,0:NAND FLASH启动
// boot_flash将在start.S中被修改
int boot_flash = 1;
char * env_name_spec;
env_t * env_ptr;

extern nor_env_get_char_spec(int index);
extern nand_env_get_char_spec(int index);
extern int nor_env_init(void);
extern int nand_env_init(void);
extern int nor_saveenv(void);
extern int nand_saveenv(void);
extern void nor_env_relocate_spec(void);
extern void nand_env_relocate_spec(void);
#ifdef ENV_IS_EMBEDDED
	extern uchar environment[];
#endif

uchar env_get_char_spec(int index)
{
	if (boot_flash) {
		return nor_env_get_char_spec(index);
	} else {
		return nand_env_get_char_spec(index);
	}
}
 
int env_init(void)
{
	if (boot_flash) {
	#ifdef ENV_IS_EMBEDDED
		env_ptr = (env_t *)(&environment[0]);
	#else
		env_ptr = (env_t *)CONFIG_ENV_ADDR;
	#endif
		env_name_spec = "Flash";
		
		return nor_env_init();
	} else {
	#if defined(ENV_IS_EMBEDDED)
		env_ptr = (env_t *)(&environment[0]);
	#elif defined(CONFIG_NAND_ENV_DST)
		env_ptr = (env_t *)CONFIG_NAND_ENV_DST;
	#else
		env_ptr = NULL;
	#endif
		env_name_spec = "NAND";
		
		return nand_env_init();
	}
}

int saveenv(void)
{
	if (boot_flash) {
		return nor_saveenv();
	} else {
		return nand_saveenv();
	}
}

void env_relocate_spec(void)
{
	if (boot_flash) {
		return nor_env_relocate_spec();
	} else {
		return nand_env_relocate_spec();
	}
}

在common/env_flash.c和common/env_nand.c中,去掉对env_name_spec和env_ptr的定义,改为外部引用:

extern char * env_name_spec;
extern env_t *env_ptr;

最后,在env_get_char_spec,env_init,saveenv和env_relocate_spec方法前分别添加前缀"nor_"和"nand_".


好了,现在编译UBoot:

make smdk2410_config && make all

下载到开发板上试试吧!

参考资料:
1. <<如何让U-boot实现Nand/Nor 双启动>>
2. <<Nand Flash 和 Nor Flash 双启动方法探究>>  关于S3C2440的
3. <<成功在skyeye 上实现U-Boot 的Nand命令并从Nand中启动Linux>>
4. <<从Nand Flash启动U-BOOT的基本原理>>
5. <<关于u-boot同时支持nand启动和Nor启动环境变量的保存位置>> 标志修改的代码放置位置好像不行,我这没有成功