第1阶段——uboot分析之通过nand命令读内核(8)

本节主要学习:
详细分析UBOOT中"bootcmd=nand read.jffs2 0x30007FC0 kernel;bootm 0x30007FC0"
怎么实现nand命令读内核.

1. nand read.jffs2 0x30007FC0 kernel
步骤a: 从NAND FILSHE中kernel分区读出
步骤b: 放到0x30007FC0去

1.1 kernel分区: 是flash中内核区
其中在flash中定义了4大分区:
| bootloader | :一开机直接运行u-boot
|boot parameters | :存放一些可以设置的参数,供u-boot使用
| kernel | :存放内核区
|root filesystem | :根文件系统,挂载(mount)后才能使用文件系统中的应用程序

这几个分区通过配置文件已在flash地址上是写好了,位于 u-boot-1.1.6/include/configs/100ask24x0.h：

#define MTDIDS_DEFAULT "nand0=nandflash0"
#define MTDPARTS_DEFAULT "mtdparts=nandflash0:256k@0(bootloader)," \
"128k(params)," \
"2m(kernel)," \
"-(root)"

在100ask24x0.h里定义了一个MTDPARTS_DEFAULT宏定义，
“mtdparts=nandflash0:”表示mtdparts分区位于nandflash上
"256k@0(bootloader),"表示从0开始共256kb是bootloader分区
"128k(params),"表示接下来128kb用来存放参数，是params分区
"2m(kernel)," 表示接下来2Mb用来存放内核,是kernel分区
"-(root)" 表示剩下的容量存放根文件系统,是root分区

1.2 可以通过在uboot界面输入"mtd"命令，查看4个分区的位置情况:
#: name size offset mask_flags
0:bootloader 0X00040000 0X00000000 0
1:params 0X00020000 0X00040000 0
2:kernel 0X00200000 0X00060000 0
3:root 0X0fda0000 0X00260000 0

从上面可以看出bootloader基地址是0x0000 0000,该分区大小为0x0004 000,所以结束地址为0X0003 FFFF。
为什么0X00040000等于256kb?
因为在ARM920t中,每隔4个地址保存了一个32位数据(4个字节)
所以0X00040000=0X00040000个字节=0x100(256)*0x400(1024)=256Kb

1.3 所以 nand read.jffs2 0x30007FC0 kernel 最终扩展开为：
nand read.jffs2 0x30007FC0 0X00060000 0X00200000

1.4 nand命令位于./common/cmd_nand.c(所有命令文件都是存在common中,以cmd_xx.c形式保存)
其中nand命令执行时调用的是do_nand(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])函数
进入do_nand()函数:

int do_nand(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])
{
int i, dev, ret;
ulong addr, off, size;
char *cmd, *s;
nand_info_t *nand;
int quiet = ;
const char *quiet_str = getenv("quiet"); //获取环境变量quiet

if (argc < ) //判断nand命令参数个数若小于2,将goto到usage,打印cmdtp->usage(nand命令短的帮助说明)
goto usage;
...
cmd = argv[]; //cmd="read.jffs2"
...
if (strcmp(cmd, "info") == ) //cmd不等于"info",不执行
{...}
...
if (strcmp(cmd, "bad") !=  && strcmp(cmd, "erase") !=  &&
strncmp(cmd, "dump", ) !=  &&
strncmp(cmd, "read", ) !=  && strncmp(cmd, "write", ) !=  &&
strcmp(cmd, "scrub") !=  && strcmp(cmd, "markbad") !=  &&
strcmp(cmd, "biterr") !=  &&
strcmp(cmd, "lock") !=  && strcmp(cmd, "unlock") !=  )
goto usage; //若argv[1]都不满足的话,表示使用命令在语法上有错误,打印短的帮助说明
....
if (strncmp(cmd, "read", ) ==  || strncmp(cmd, "write", ) == ) //cmd==read为真
{
int read;

if (argc < ) // "nand read.jffs2 0x30007FC0 0X00060000 0X00200000"共5个参数,这里不执行
goto usage;

addr = (ulong)simple_strtoul(argv[], NULL, ); //将argv[2]的"0x30007FC0"字符型转换成数值型

read = strncmp(cmd, "read", ) == ;
//strncmp():判断cmd和"read"前4个字节若相等返回0,不相等返回大于0的数
//这里cmd与"read"相等，所以strncmp()返回0,read=(0==0)为真,所以read=1
printf("\nNAND %s: ", read ? "read" : "write"); //由于read=1,所以打印"\nNAND read:" 

if (arg_off_size(argc - , argv + , nand, &off, &size) != )
return ;

s = strchr(cmd, '.'); //strchr():查找'.'字符,若没找到返回NULL。
if (s != NULL &&
(!strcmp(s, ".jffs2") || !strcmp(s, ".e") || !strcmp(s, ".i"))) //if为真,argv[1]=read.jffs2
{
if (read) { //read==1,执行if
/* read */
nand_read_options_t opts;
memset(&opts, , sizeof(opts));
opts.buffer = (u_char*) addr; //设置buffer=0x30007FC0
opts.length = size; //设置size=0X00200000=2097152 byte
opts.offset = off; //设置offset=0X00060000
opts.quiet = quiet;
ret = nand_read_opts(nand, &opts);
//nand_read_opts():读取nandflash的kernel分区到 buffer地址,如读取成功返回0
} else {
/* write */
...
}
}
else if ( s != NULL && !strcmp(s, ".yaffs")){
...
}else if ( s != NULL && !strcmp(s, ".raw")){
...
} else {
...
}

printf(" %d bytes %s: %s\n", size,
read ? "read" : "written", ret ? "ERROR" : "OK"); //打印"2097152 bytes read : OK\n"

return ret ==  ?  : ; //read读取kernel分区成功返回0,失败返回1
}