Embedded linux boot

-


 

General booting sequence:


  • RBL (ROM Boot loader):
    • Provided By:  chip manufacture.
    • code location: ROM of the SOC.
    • code execution: ROM
    • Job: 
      • Load and execute 2nd stage boot loader(SPL/MLO) internal memory of SOC
      • Watchdog initialization (3 minutes). if it does not detect any 2nd stage Boot loader(memory booting or peripheral booting ). reset the soc.
      • System clock configuration using PLL.
      • Copy MLO/SPL into the internal SRAM of the chip from eMMC Memory
      • Execute SPL.
  • SPL Boot loader:
    • Provided by: open source 
    • code location: SD card (1st partition)
    • code execution: SRAM (64K) (internal RAM) 
    • Job:
      • load and execute the 3rd state boot loader such as Uboot.
      • UART console initialization to print out debug message.
      • Initializes the DDR registers to use DDR Memory.  
      • Mux configuration of boot peripherals pins.
      • Copy the Uboot in DRAM from eMMC Memory.
  • Uboot Boot loader:
    • Provided by:  Open 
    • code location: SD card (2nd partition) /boot
    • code execution:  DRAM(512KB)
    • Job:
      • load and execute the Linux kernel from DDR.
      • Initialize some of the peripherals like I2c, NAND, ethernet, UART, (kernel loading support peripheral).
      • Load Linux kernel image from various boot sources(USB, NAND flash, Network,eMMC, SD card, serial port)  to the DDR memory of the board. 
  • Kernel:
    • Provided by: open source
    • code location: SD card
    • code execution: DRAM  
    • Job: 
      • see below

Kernel booting:

    

File path:

  • linux/arch/arm/boot/compressed/head.S' --> boot startp staring point
  • linux/arch/arm/kernel/head.S       --> belongs linux kernel arch specific code most does cpu specifice initialization of SOC (arm cortex a8 CPU)
  • linux/arch/arm/kernel/head-common.S    --> all the architure specifice initlize 
  • linux/init/main.c -->  starting point of linux kernel,
    • linux banner --> linux version, date of build linux version
    • start_kernel will call the rest_kernel, which will again call the kernel_init thread. 
      • cgroup_init_early
      • boot cpu init
      • page alloc init
      • timer init 
      • profile init 
      • mmu init 
      • IRQ init
      • console init.
    • in that thread , it will check for the  /sbin/init 
  • /sbin/init sourece code, will be present in  uclinux-rootfs/user/busybox/init/init.c


Q & A:
  •  Can we avoid using the MLO/SPL by making RBL directly load the uboot into internal Memory SRAM? 
    • The Size of the internal RAM is 128Kbytes. (in that 128KB, some part is reserved for the STACK & Heap). uboot image is not possible to reduce < 128KB. 
  • Can we use RBL to load U-boot directly into DDR memory of the board and skip using MLO/SPL?
    • ROM code won't be having any idea about what kind of DDR RAM being used in the product to initialize it. 
    • DDR RAM is product specific. 

Comments

Post a Comment

Popular posts from this blog

Overview of ISO/SAE 21434 Standard

-
Image
ISO/SAE 21434, jointly published by the International Standardization Organization (ISO) and the Society of Automotive Engineers (SAE), serves as a comprehensive cybersecurity framework for electronic systems within road vehicles. Developed to bolster cybersecurity across the entire lifecycle of automotive products, this standard outlines essential vocabulary, objectives, requirements, and guidelines. Purpose and Scope: The primary objective of ISO/SAE 21434 is to enhance cybersecurity measures for vehicles throughout their lifecycle. By providing a standardized framework, this standard facilitates the establishment of cybersecurity policies, risk management practices, and a cybersecurity-oriented culture within organizations operating in the automotive industry. Three Pillars: ISO/SAE 21434 is structured around three main pillars: Cyber Security Governance:   Establishing policies, processes, and cultural norms to govern cybersecurity activities within organizations. Risk Man...
Read more

Fundamental Secure Feature I: Secure Boot

-
Image
What is it? Secure Boot is a mechanism that verifies the authenticity and integrity of software code stored in flash memory before allowing the system to execute it. The MCU will only boot the application if the code has not been tampered with. Why is it needed? Prevents unauthorized firmware execution. Protects against malicious code injection during the boot process. Blocks attempts to bypass security checks by tampering with the bootloader. Ensures the ECU does not boot into a compromised or corrupted state. 🔍 For example, an attacker might modify the bootloader to disable security features after boot. Secure Boot prevents this by enforcing integrity checks from the very first instruction. Types of Secure Boot: Symmetric-Based Secure Boot Uses shared keys for both signing and verification. Easier to implement, but key management is critical. Asymmetric-Based Secure Boot Uses a private-public key pair. The bootloader verifies the signature of the firmware using a public key, while t...
Read more

Cryptography and Encryption Basics - I

-
Image
Cryptography and Encryption Basics I What is encryption Encryption is the process of encoding a message or information in such a way that only authorized parties can access it and those who are not authorized can't.  Converts information from plain text into encrypted ciphertext. But how...? Encryption used algorithm! An algorithm is a procedure that the encryption process follows. The specific algorithm is called the ciper or code. there are many types so encryption algorithms. The encryption's goal and level of security determine the most effective solution. Triple DES, RSA and Blowfish are some examples of encryption algorithms or Ciphers. What is Decryption? Decryption is the process of taking encoded or encrypted text or other data and converting it back into text that you or the computer can read and understand.  converts information from encrypted ciphertext into plain text  Basic Example  Private key vs Public Key Private Key (symmetric key): This means that ...
Read more