L3 boot process

Power on -> booting from permanent memory (or booting from and devices) -> loading OS -> loading processes……

Why four loaders are necessary

  • first loader (bootloader in permanent memory such as ROM/NOR flash/randomly access and byte addressable)

    • Process can run but knows nothing about the whole system
    • ==prepared by SoC vendors or motherboard vendors== to make sure there is no problem with whole system (CPU藉由program去了解周邊的環境跟裝置是啥) （很可能是出廠前就燒好的）

      SoC: System on memory

    • ==check/initialize the hardware==
    • May provide basic services to other program (API之類的？？，讓你去access某些硬體之類的)
    • May provide shells to end-users for basic operations.
    • Load/jump to the secod loader (based on predefined procedures/configurations)

  • Second loader (bootloader in any devices such as DISK/CD-ROM/NAND flash/remote server/…) (放在另外的裝置上)

    • As soon as first bootloader can access the secod loader (on any device), load it into memory, and can jump to the starting instruction
    • ==Prepare by OS vendors== or other third party vendors
      • Stored in the correct location/in correct format
      • Must know how to load OSs
    • May provide shell to end-user to select OSs(multi-booting) or set configurations
    • ==Goal==: Loading OS into memory
    • Optional for emdedded processors

  • third loader (OS loader that loads OS)

    • A program executes without OS serivces
    • Initial and prepare OS services

  • Fourth loader (processes replies on OS to fork/exec other program)

    • OS is now ready and can provide services
    • Any process calls OS services to fork/execute other processes

First boot-loader functions

  • initialize(reset) the hardware setting
    • Power on self-test in x86/OS
  • Basic monitor and debugger
  • Pass the control to 2nd bootloader

跳到memory執行second bootloader是因為2nd bootloader需要比較大的空間之類的


應該是first bootloader

  • POST: power on self-test
  • 一開始的時候就是直接到specific location去拿東西

discussion

  • CPU本身沒有driver
  • vector table -> 指向其他device的記憶體的東西
  • 開機
    • 在完整開機之下，要從BIOS開始，從沒有作業系統開始開，要把OS從hardware搬進Memory
    • 睡眠的話，就是在已經有OS之下再開