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sunxi学习：[0]全志SoC启动过程分析

参考：

启动流程：Boot ROM→SPL→U-boot(→Kernel→RootFileSystem)

一、BROM阶段

全志SoC有一个非常具体的启动过程。首先，它执行一个微小的片上 Boot ROM（BROM），然后检查按钮的FEL模式，然后开始检查各种存储选项的有效的引导签名在正确的位置。

上电后，SoC开始从BROM所在的地址0xffff0000获取指令。BROM分为两部分：第一部分（0xffff0000）是FEL模式，第二部分是eGON.BRM（位于0xffff4000）。

FEL:FEL是包含在Allwinner设备上的BootROM中的低级子例程。它用于使用USB的设备的初始编程和恢复。所以，全志平台一般不会砖，就是有这个FEL。

一般来说，BROM首先检查SD卡(SD/MMC)启动可用性，其次再检查Nand Flash是否可以启动，然后再检查SPI Nor Flash的启动可用性，如果都无法启动则进入 FEL 模式。当程序初始化启动介质成功后，就从固定位置读入bootloader的Boot0到SRAM，然后跳到SRAM执行。

将u-boot烧录进SD卡

SD Card Layout：

根据SD Card Layout表，使用dd将u-boot烧录进SD卡：

sudo dd if=u-boot-sunxi-with-spl.bin of=${card} bs=1024 seek=8

二、U-boot SPL阶段

SPL(Secondary Program Loader)程序流程如下：

• 初始化ARM处理器
• 初始化串口控制台
• 配置时钟和最基础的分频
• 初始化SDRAM
• 配置引脚多路复用功能
• 启动设备初始化（即上面选择的启动设备）
• 加载完整的u-boot/kernel程序并转交控制权

使用FEL/USBBoot启动spl

sudo ./sunxi-fel uboot u-boot-sunxi-with-spl.bin

U-Boot SPL 2017.03-rc2-gc7a25b3-dirty (Mar 11 2017 - 17:09:43)DRAM: 256 MiBTrying to boot from FEL

三、U-boot

由SPL引导进入的U-boot：

U-Boot 2017.03-rc2-gc7a25b3-dirty (Mar 11 2017 - 17:09:43 +0800) Allwinner TechnologyCPU:   Allwinner H3 (SUN8I 1680)Model: Xunlong Orange Pi ZeroDRAM:  256 MiBMMC:   SUNXI SD/MMC: 0MMC: no card presentmmc_init: -123, time 1*** Warning - MMC init failed, using default environmentIn:    serialOut:   serialErr:   serialNet:   phy interface0eth0: ethernet@1c30000starting USB...USB0:   USB EHCI 1.00USB1:   USB OHCI 1.0scanning bus 0 for devices... 1 USB Device(s) found       scanning usb for storage devices... 0 Storage Device(s) foundHit any key to stop autoboot:  0 u-boot@sun8i $ ??       - alias for 'help'base    - print or set address offsetbdinfo  - print Board Info structureboot    - boot default, i.e., run 'bootcmd'bootd   - boot default, i.e., run 'bootcmd'bootefi - Boots an EFI payload from memorybootelf - Boot from an ELF image in memorybootm   - boot application image from memorybootp   - boot image via network using BOOTP/TFTP protocolbootvx  - Boot vxWorks from an ELF imagebootz   - boot Linux zImage image from memorycmp     - memory compareconinfo - print console devices and informationcp      - memory copycrc32   - checksum calculationdhcp    - boot image via network using DHCP/TFTP protocoldm      - Driver model low level accessecho    - echo args to consoleeditenv - edit environment variableenv     - environment handling commandsexit    - exit scriptext2load- load binary file from a Ext2 filesystemext2ls  - list files in a directory (default /)ext4load- load binary file from a Ext4 filesystemext4ls  - list files in a directory (default /)ext4size- determine a file's sizefalse   - do nothing, unsuccessfullyfatinfo - print information about filesystemfatload - load binary file from a dos filesystemfatls   - list files in a directory (default /)fatsize - determine a file's sizefatwrite- write file into a dos filesystemfdt     - flattened device tree utility commandsfstype  - Look up a filesystem typego      - start application at address 'addr'gpio    - query and control gpio pinshelp    - print command description/usageiminfo  - print header information for application imageimxtract- extract a part of a multi-imageitest   - return true/false on integer compareload    - load binary file from a filesystemloadb   - load binary file over serial line (kermit mode)loads   - load S-Record file over serial lineloadx   - load binary file over serial line (xmodem mode)loady   - load binary file over serial line (ymodem mode)loop    - infinite loop on address rangels      - list files in a directory (default /)md      - memory displaymdio    - MDIO utility commandsmii     - MII utility commandsmm      - memory modify (auto-incrementing address)mmc     - MMC sub systemmmcinfo - display MMC infomw      - memory write (fill)nfs     - boot image via network using NFS protocolnm      - memory modify (constant address)part    - disk partition related commandsping    - send ICMP ECHO_REQUEST to network hostprintenv- print environment variablespxe     - commands to get and boot from pxe filesreset   - Perform RESET of the CPUrun     - run commands in an environment variablesave    - save file to a filesystemsaveenv - save environment variables to persistent storagesetenv  - set environment variablessetexpr - set environment variable as the result of eval expressionshowvar - print local hushshell variablessize    - determine a file's sizesleep   - delay execution for some timesource  - run script from memorysysboot - command to get and boot from syslinux filestest    - minimal test like /bin/shtftpboot- boot image via network using TFTP protocoltrue    - do nothing, successfullyusb     - USB sub-systemusbboot - boot from USB deviceversion - print monitor, compiler and linker versionu-boot@sun8i $

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