一、【linux启动】嵌入式Linux系统启动过程分析

一、概述

嵌入式linux系统启动过程一般包含以下几个过程：

• 上电
• 执行IROM(芯片内部只读存储器)中固化的代码。
• 执行uboot
• 加载内核到内存，启动内核。
• 挂载根文件系统rootfs
• 执行其中的脚本和应用程序。

二、linux操作系统的几个组成部分介绍

1、uboot介绍

（1）概述

• 是一个通用的bootloader

• Boot:完成硬件的初始化

• Loader:加载操作系统内核，并启动内核.

• uboot支持多种处理器架构：ARM、PowerPC 、X86 、 Mips等等。

• 支持加载启动多种操作系统：linux、wince、VXworks等

• uboot的源码下载地址：https://ftp.denx.de/pub/u-boot/

（2）作用

• CPU的初始化（芯片级）主要采用ARM汇编语言，包含初始化缓存、MMC、Watchdog、终端、clock等。
• 板级初始化（采用C语言编写）：主要初始化串口、网卡、USB、LCD等设备.

• 为操作系统的启动准备参数，加载操作系统镜像到内存，并启动.

(3)u-boot的开机打印信息分析

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U-Boot 2014.07 (Apr 10 2021 - 02:16:01)---U-boot版本号   //时钟系统中各个总线上的时钟频率 PLL : [0] =  800000000, [1] =  800000000, [2] =  780000000, [3] =  800000000 (0) PLL1: CPU  FCLK =  800000000, HCLK = 200000000 (G0) (7) PLL1: CPU  FCLK =  800000000, HCLK = 200000000 (G1) (2) PLL3: MEM  FCLK =  800000000, DCLK = 800000000, BCLK = 400000000, PCLK = 200000000 (1) PLL0: BUS  BCLK =  400000000, PCLK = 200000000 (8) PLL0: CCI4 BCLK =  400000000, PCLK = 200000000 (3) PLL0: G3D  BCLK =  400000000 (4) PLL0: CODA BCLK =  400000000, PCLK = 200000000 (5) PLL0: DISP BCLK =  400000000, PCLK = 200000000 (6) PLL0: HDMI PCLK =  133333333 I2C:   ready DRAM:  1 GiB------------内存1GB Heap = 0x44000000~0x46000000 Code = 0x43c00000~0x43c83e48 GLD  = 0x43bffeb8 GLBD = 0x43bffe68 SP   = 0x43bffe68,0x43bffe48(CURR) PC   = 0x43c06640 TAGS = 0x40000100 PAGE = 0x43c90000~0x43c9c000 MACH = [4330]   VER  = 0      BOARD= [GEC6818]    MMC:   NXP DWMMC: 0, NXP DWMMC: 1, NXP DWMMC: 2 In:    serial Out:   serial Err:   serial ## DCDC_MODE(0x80): DCDC1[PFM], DCDC2[PFM], DCDC3[PFM], DCDC4[PWM], DCDC5[PWM] ## STATUS(0x00)   : 0xe4 0x10 ## IRQ(0x48)      : 0x00 0x00 0x00 0x00 0x00 ## CHG_TYPE       : ADP ## BAT_VOL        : 0mV ## BAT_CAP        : 100% DONE: Logo bmp 300 by 300 (3bpp), len=270056 DRAW: 0x47000000 -> 0x46000000 DONE: Logo bmp 300 by 300 (3bpp), len=270056 DRAW: 0x47000000 -> 0x46000000 RGB: display.0 MIPI: display.0 DSIM_ESCMODE 1 : 0xc0 DSIM_STATUS : 0x10010f MIPI clk:  420MHz DSIM_ESCMODE 2 : 0x0 DSIM_STATUS : 0x10010f ## Skip BAT Animation. ## IRQ(0x48)   : 0x00 0x00 0x00 0x00 0x00 ## chg_type    : ADP ## battery_vol : 0mV ## battery_cap : 100% ## Booting Card did not respond to voltage select! Net:   GEC6818 mac init... dwmac.c0060000 Hit any key to stop autoboot:  0---倒计时结束加载启动内核，倒计时结束前按下键盘上的任意按键，进入U-BOOT命令行

（4）uboot的命令

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=> help   //在uboot下执行help看uboot下的帮助文档 ?         - alias for 'help' base      - print or set address offset bdinfo    - print Board Info structure blkcache  - block cache diagnostics and control boot      - boot default, i.e., run 'bootcmd' bootd     - boot default, i.e., run 'bootcmd' bootefi   - Boots an EFI payload from memory bootelf   - Boot from an ELF image in memory bootm     - boot application image from memory bootp     - boot image via network using BOOTP/TFTP protocol bootvx    - Boot vxWorks from an ELF image bootz     - boot Linux zImage image from memory cmp       - memory compare coninfo   - print console devices and information cp        - memory copy crc32     - checksum calculation dhcp      - boot image via network using DHCP/TFTP protocol dm        - Driver model low level access echo      - echo args to console editenv   - edit environment variable env       - environment handling commands erase     - erase FLASH memory exit      - exit script ext2load  - load binary file from a Ext2 filesystem ext2ls    - list files in a directory (default /) ext4load  - load binary file from a Ext4 filesystem ext4ls    - list files in a directory (default /) ext4size  - determine a file's size false     - do nothing, unsuccessfully fatinfo   - print information about filesystem fatload   - load binary file from a dos filesystem fatls     - list files in a directory (default /) fatmkdir  - create a directory fatrm     - delete a file fatsize   - determine a file's size fatwrite  - write file into a dos filesystem fdt       - flattened device tree utility commands flinfo    - print FLASH memory information fstype    - Look up a filesystem type go        - start application at address 'addr' gpio      - query and control gpio pins gpt       - GUID Partition Table help      - print command description/usage iminfo    - print header information for application image imxtract  - extract a part of a multi-image itest     - return true/false on integer compare ln        - Create a symbolic link load      - load binary file from a filesystem loadb     - load binary file over serial line (kermit mode) loads     - load S-Record file over serial line loadx     - load binary file over serial line (xmodem mode) loady     - load binary file over serial line (ymodem mode) loop      - infinite loop on address range ls        - list files in a directory (default /) md        - memory display mdio      - MDIO utility commands mii       - MII utility commands mm        - memory modify (auto-incrementing address) mmc       - MMC sub system mmcinfo   - display MMC info mtd       - MTD utils mw        - memory write (fill) nfs       - boot image via network using NFS protocol nm        - memory modify (constant address) part      - disk partition related commands ping      - send ICMP ECHO_REQUEST to network host printenv  - print environment variables protect   - enable or disable FLASH write protection pxe       - commands to get and boot from pxe files random    - fill memory with random pattern reset     - Perform RESET of the CPU run       - run commands in an environment variable save      - save file to a filesystem saveenv   - save environment variables to persistent storage setenv    - set environment variables setexpr   - set environment variable as the result of eval expression sf        - SPI flash sub-system showvar   - print local hushshell variables size      - determine a file's size sleep     - delay execution for some time source    - run script from memory sysboot   - command to get and boot from syslinux files test      - minimal test like /bin/sh tftpboot  - boot image via network using TFTP protocol true      - do nothing, successfully usb       - USB sub-system usbboot   - boot from USB device version   - print monitor, compiler and linker version

• bdinfo:打印出开发板的信息

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GEC6818# bdinfo arch_number = 0x000010EA-------开发板的编号，要与内核源码中开发板编号一致 boot_params = 0x40000100-------启动内核所需参数在内存的0x40000100处 DRAM bank   = 0x00000000 -> start    = 0x40000000-----------内存的起始地址，结束地址0x7fffffff -> size     = 0x40000000-----------内存的大小  1GB eth0name    = dwmac.c0060000---网卡的名字 ethaddr     = 00:e2:1c:ba:e8:60 --网卡的MAC地址 current eth = dwmac.c0060000 ip_addr     = 192.168.51.5----------U-BOOT设置的网卡IP baudrate    = 115200 bps-----------串口的波特率 TLB addr    = 0x7FFF0000 relocaddr   = 0x46000000 reloc off   = 0x00000000 irq_sp      = 0x7DF6BF00 sp start    = 0x43BFFE6

• 启动内核的命令

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boot    - boot default, i.e., run 'bootcmd' bootd   - boot default, i.e., run 'bootcmd' bootm   - boot application image from memory bootp   - boot image via network using BOOTP/TFTP protocol

• printenv：打印环境变量

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GEC6818# printenv baudrate=115200 bootargs=lcd=at070tn92 tp=gslx680-linux root=/dev/mmcblk0p2 rw rootfstype=ext4 bootcmd=ext4load mmc 2:1 0x48000000 uImage;bootm 0x48000000

两个重要的环境变量：

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bootargs启动参数：告诉内核一些重要启动信息 lcd=at070tn92-------------LCD屏驱动芯片的型号 tp=gslx680-linux-----------触摸屏的型号 root=/dev/mmcblk0p2----根文件系统在emmc的第2个分区 rw rootfstype=ext4--------根文件系统可读可写，类型是ext4   bootcmd--------------------启动命令环境变量,告诉U-boot一些信息 bootcmd=ext4load mmc 2:1 0x48000000 uImage;bootm 0x48000000 以ext4格式把内核镜像uImage从emmc的第1分区加载到内存的0x48000000处，然后去到内存0x48000000处，启动内核 bootdelay=3---------------倒计时3S bootfile=uImage ethact=dwmac.c0060000 ethaddr=00:e2:1c:ba:e8:60 ethprime=RTL8211------网卡芯片的型号   gatewayip=192.168.51.1-----------------默认网关 ipaddr=192.168.51.5---------------------开发板IP netmask=255.255.255.0----------------子网掩码 qtcrc=-1489582083 serverip=192.168.51.2-------------------服务器IP stderr=serial stdin=serial stdout=serial

• setenv ：设置（修改）环境变量的值

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GEC6818# setenv bootdelay 5  -----------把环境变量bootdelay的值修改为5 GEC6818# saveenv-----------------------------保存环境变量的修改 Saving Environment to MMC... Writing to MMC(2)... doner

• reset:重启主板
• go:去到内存某个地址执行程序。

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1 2	GEC6818# go 0x40000000------------去到内存0x40000000处，执行程序 ## Starting application at 0x40000000 ..

• ping ：测试网络连通性

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Environment size: 843/32764 bytes GEC6818# setenv ipaddr 192.168.1.21 -----设置开发板自己的IP GEC6818# setenv netmask 255.255.255.0 GEC6818# setenv gatewayip 192.168.1.1 GEC6818# setenv serverip 192.168.1.20 GEC6818# saveenv Saving Environment to MMC... Writing to MMC(2)... done   Writing to MMC(2)... done GEC6818# ping 192.168.1.20 Speed: 100, full duplex Using dwmac.c0060000 device host 192.168.1.20 is alive----------------网络连通

• tftp:运行tftpd32.exe，相当于在windows下搭建了tftp服务器

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GEC6818# setenv serverip 192.168.1.20---在开发板U-BOOT中设置服务器IP为windows IP GEC6818# save Saving Environment to MMC... Writing to MMC(2)... done   GEC6818# tftp 0x40000000 tftpd32.ini-----从tftp服务器上下载一个名字为tftpd32.ini的文件到内存0x40000000处   Speed: 100, full duplex Using dwmac.c0060000 device TFTP from server 192.168.1.20; our IP address is 192.168.1.21 Filename 'tftpd32.ini'. Load address: 0x40000000 Loading: #          7.8 KiB/s done Bytes transferred = 530 (212 hex)

2、内核

（1）内核的作用

• 进程调度与进程通信

• 内存管理
• 文件管理
• 设备驱动管理
• 网络通信---TCP/IP

kernel源码下载地址：https://mirrors.edge.kernel.org/pub/linux/kernel/

（2）linux内核启动时的输出信息

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## Booting kernel from Legacy Image at 48000000 ...    Image Name:   Linux-3.4.39-gec -----------内核版本                     　　3 主版本号                     　　4 次版本号 偶数：稳定版 奇数：开发版                     　　39 修订版本号                     　　Gec 扩展版本号      Image Type:   ARM Linux Kernel Image (uncompressed)    Data Size:    5575624 Bytes = 5.3 MiB    Load Address: 40008000    Entry Point:  40008000    Verifying Checksum ... OK    Loading Kernel Image ... OK   Starting kernel ...  --------------------开始启动内核   [    0.000000] Booting Linux on physical CPU 0 -------------在CPU0 上启动Linux     [    0.000000] Memory: 1024MB = 1024MB total [    0.000000] Memory: 810728k/810728k available, 237848k reserved, 272384K highmem   虚拟内存的划分 [    0.000000] Virtual kernel memory layout: [    0.000000]     vector  : 0xffff0000 - 0xffff1000   (   4 kB) [    0.000000]     fixmap  : 0xfff00000 - 0xfffe0000   ( 896 kB) [    0.000000]     vmalloc : 0xef800000 - 0xfee00000   ( 246 MB) [    0.000000]     lowmem  : 0xc0000000 - 0xef600000   ( 758 MB) [    0.000000]     pkmap   : 0xbfe00000 - 0xc0000000   (   2 MB) [    0.000000]     modules : 0xbf000000 - 0xbfe00000   (  14 MB) [    0.000000]       .text : 0xc0008000 - 0xc0a65214   (10613 kB) [    0.000000]       .init : 0xc0a66000 - 0xc0aa3100   ( 245 kB) [    0.000000]       .data : 0xc0aa4000 - 0xc0b3ec88   ( 620 kB) [    0.000000]        .bss : 0xc0b3ecac - 0xc0d203c8   (1926 kB)   外设的初始化 [    0.173000] usbcore: registered new interface driver usbfs [    0.174000] usbcore: registered new interface driver hub [    0.174000] usbcore: registered new device driver usb [    0.174000] i2c-gpio i2c-gpio.0: using pins 99 (SDA) and 98 (SCL) [    0.175000] i2c-gpio i2c-gpio.3: using pins 80 (SDA) and 79 (SCL) [    0.176000] s3c-i2c s3c2440-i2c.1: i2c-1: S3C I2C adapter [    0.176000] s3c-i2c s3c2440-i2c.1: slave address 0x10 [    0.176000] s3c-i2c s3c2440-i2c.1: bus frequency set to 97 KHz [    0.178000] s3c-i2c s3c2440-i2c.2: i2c-2: S3C I2C adapter [    0.178000] s3c-i2c s3c2440-i2c.2: slave address 0x10 [    0.178000] s3c-i2c s3c2440-i2c.2: bus frequency set to 97 KHz   网络协议 [    0.331000] NET: Registered protocol family 2 [    0.331000] IP route cache hash table entries: 32768 (order: 5, 131072 bytes) [    0.332000] TCP established hash table entries: 131072 (order: 8, 1048576 bytes) [    0.334000] TCP bind hash table entries: 65536 (order: 8, 1572864 bytes) [    0.336000] TCP: Hash tables configured (established 131072 bind 65536) [    0.336000] TCP: reno registered [    0.336000] UDP hash table entries: 512 (order: 3, 32768 bytes) [    0.336000] UDP-Lite hash table entries: 512 (order: 3, 32768 bytes) [    0.337000] NET: Registered protocol family 1 [    0.337000] RPC: Registered named UNIX socket transport module. [    0.337000] RPC: Registered udp transport module. [    0.337000] RPC: Registered tcp transport module. [    0.337000] RPC: Registered tcp NFSv4.1 backchannel transport module.   挂载根文件系统 [    5.996000] VFS: Mounted root (ext4 filesystem) on device 179:2. [    6.003000] devtmpfs: mounted [    6.005000] Freeing init memory: 244K [    6.009000] Write protecting the kernel text section c0008000 - c0a2f000 [    6.016000] rodata_test: attempting to write to read-only section: [    6.022000] write to read-only section trapped, success [    6.166000] EXT4-fs (mmcblk0p2): re-mounted. Opts: data=ordered [    6.539000] eth0: device MAC address 6e:3a:61:c8:01:f4 [    6.546000] stmmac_open: failed PTP initialization   可以用mount命令查看所有的挂载信息和文件系统格式 [root@GEC6818 /]#mount rootfs on / type rootfs (rw) /dev/root on / type ext4 (rw,sync,relatime,data=ordered) devtmpfs on /dev type devtmpfs (rw,relatime,size=405364k,nr_inodes=101341,mode=755) proc on /proc type proc (rw,relatime) devpts on /dev/pts type devpts (rw,relatime,gid=5,mode=620) tmpfs on /dev/shm type tmpfs (rw,relatime,mode=777) tmpfs on /tmp type tmpfs (rw,relatime) tmpfs on /run type tmpfs (rw,nosuid,nodev,relatime,mode=755) sysfs on /sys type sysfs (rw,relatime）

3、根文件系统　　

（1）概述

　　根文件系统是一个“包”，里面包含很多内容

•  shell命令和可执行程序：/bin   /sbin   /usr/bin
• 设备文件：  /dev
• 配置文件或脚本/etc  例如：/etc/profile就是一个脚本
• 库文件（动态库）   *.so     /lib   /usr/lib 
• /proc  该目录下的文件，存放了系统运行的实时状态信息

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[root@GEC6818 /]#ls /proc/ 1              22             49             buddyinfo      meminfo 10             23             5              bus            misc 100            24             50             cgroups        modules 101            25             51             cmdline        mounts 102            26             52             config.gz      net 103            27             53             consoles       pagetypeinfo 104            28             6              cpu            partitions 105            29             7              cpuinfo        sched_debug

以数字命名的目录文件,数字是进程的PID，目录下文件中存储的是进程的状态信息

• /sys 该目录下的文件存储了驱动相关信息
• /mnt ------挂载点
• /usr-----用户程序或库文件
• /opt ------第三方的大软件
• /val--------------系统日志目录

根文件系统挂载后：

• 执行脚本/etc/init.d/rcS
• 执行/etc/profile
• 装载驱动模块
• 执行iot应用程序。