Boot Process

Overview

This document details the boot process for NXP ARM-based development boards running Linux and Android operating systems. The boot sequence follows a multi-stage architecture from power-on to full OS initialization.

Boot Process Architecture

graph TD
    A[Power On/Reset] --> B[Boot ROM<br/>On-Chip ROM];
    B --> C{Boot Mode Selection<br/>eMMC/SD/USB/UART};
    
    subgraph "i.MX 8 Series"
        C --> D1[i.MX 8 Boot Flow];
        D1 --> E1[SCFW → SPL → ATF];
        E1 --> F1[U-Boot → Linux/Android];
    end
    
    subgraph "i.MX 6/7 Series"
        C --> D2[i.MX 6/7 Boot Flow];
        D2 --> E2[DCD → SPL → U-Boot];
        E2 --> F2[Linux Kernel];
    end
    
    subgraph "Layerscape Series"
        C --> D3[Layerscape Boot Flow];
        D3 --> E3[RCW → U-Boot → PPA];
        E3 --> F3[Linux/DPDK];
    end
    
    subgraph "Kinetis Series"
        C --> D4[Kinetis Boot Flow];
        D4 --> E4[XIP/MCUBoot];
        E4 --> F4[RTOS/Embedded];
    end
    
    F1 --> G[Device Tree Init];
    F2 --> G;
    F3 --> G;
    F4 --> G;
    
    G --> H[Kernel Initialization];
    H --> I[Init Process];
    I --> J[Userspace];
    
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style J fill:#ccf,stroke:#333,stroke-width:2px
    style D1 fill:#d4f7d4
    style D2 fill:#d4e6f7
    style D3 fill:#f7d4e6
    style D4 fill:#f7f2d4

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Board-Specific Boot Flows

1. i.MX 8 Series (i.MX 8M/8M Mini/8M Plus/8QM)

graph LR
    A[Boot ROM] --> B[Load SCFW<br/>System Controller];
    B --> C[SCFW loads SPL];
    C --> D[SPL loads ATF<br/>ARM Trusted Firmware];
    D --> E[ATF loads U-Boot];
    E --> F{U-Boot Actions};
    F --> G[Load DTB];
    F --> H[Load Kernel];
    F --> I[AVB Verification];
    G & H & I --> J[Boot Linux/Android];

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Key Components:

• SCFW: System Controller Firmware (manages power, clocks, security)
• ATF: ARM Trusted Firmware (EL3 secure monitor)
• OPTEE: Optional TEE for secure applications
• AVB: Android Verified Boot (for Android images)

Typical Boards: i.MX 8M EVK, i.MX 8M Mini EVK, i.MX 8M Plus EVK

2. i.MX 6/7 Series (i.MX 6Quad/6Dual/6Solo/7Dual)

graph LR
    A[Boot ROM] --> B[Read DCD<br/>Device Config Data];
    B --> C[Initialize DDR];
    C --> D[Load SPL<br/>Secondary Program Loader];
    D --> E[SPL loads U-Boot];
    E --> F{U-Boot Phase};
    F --> G[Setup Board];
    F --> H[Load Kernel];
    F --> I[Load DTB];
    G & H & I --> J[Boot Linux];

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Key Components:

• DCD: Device Configuration Data (DDR timing parameters)
• IVT: Image Vector Table (image header structure)
• HAB: High Assurance Boot (security enforcement)

Typical Boards: Sabre SD, Sabre AI, i.MX 7Dual SABRE

3. Layerscape Series (LX2160A, LS1046A, LS1028A)

graph LR
    A[Power On] --> B[Load RCW<br/>Reset Configuration Word];
    B --> C[Initialize SerDes];
    C --> D[Load U-Boot];
    D --> E[Load PPA<br/>Platform Partition];
    E --> F[Setup DPC<br/>DPAA2 Complex];
    F --> G[Load Linux/DPDK];
    G --> H[Run Applications];

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Key Components:

• RCW: Reset Configuration Word (pin multiplexing, SerDes config)
• PPA: Platform Partition Architecture (firmware partition)
• DPAA2: Data Path Acceleration Architecture

Typical Boards: Layerscape LX2160ARDB, LS1046ARDB, LS1028ARDB

4. Kinetis Series (K64, K66, K28)

graph LR
    A[Reset] --> B[Boot ROM];
    B --> C{Flash Type};
    C --> D[XIP Execution];
    C --> E[Load to RAM];
    D & E --> F[MCUBoot<br/>Optional];
    F --> G[RTOS/Embedded App];
    G --> H[Run Application];

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Key Components:

• XIP: Execute-In-Place (run directly from flash)
• MCUBoot: Secure bootloader for MCUs
• FlexSPI: External flash interface

Typical Boards: FRDM-K64F, FRDM-K66F, TWR-K28F

Common Boot Components

Boot Media Options

Media Type	Typical Use	Speed	Capacity
eMMC	Primary storage	High	4GB-64GB
SD Card	Development	Medium	Up to 512GB
QSPI Flash	Boot device	Medium	16MB-256MB
NAND Flash	Cost-sensitive	Medium	256MB-2GB
USB	Recovery/Download	Variable	N/A

Security Features

• HAB (High Assurance Boot): Code signing and verification
• CAAM (Cryptographic Accelerator): Hardware crypto engine
• TrustZone: ARM security extension
• AVB 2.0: Android Verified Boot
• Secure JTAG: Debug port protection

Boot Configuration

# Typical U-Boot environment variables
bootcmd=mmc dev ${mmcdev}; mmc read ${loadaddr} ${kernel_addr} ${kernel_size}; \
        mmc read ${fdt_addr} ${fdt_addr_r} ${fdt_size}; \
        bootz ${loadaddr} - ${fdt_addr}

bootargs=console=ttymxc0,115200 root=/dev/mmcblk1p2 rootwait rw

Quick Reference

Boot Mode Selection

Boot Pins	Mode	Description
0000	Serial Downloader	USB/UART recovery
0001	Internal Boot	Normal boot from flash
0010	USB Boot	Boot from USB device
0100	SD Card	Boot from SD/MMC

Common Commands

# U-Boot commands for i.MX
=> mmc list          # List MMC devices
=> fatls mmc 0:1     # List files on FAT partition
=> boot              # Boot with default settings
=> run netboot       # Network boot
=> fastboot          # Enter fastboot mode

Troubleshooting

Common Issues

1. Boot hangs at SPL: Check DDR initialization parameters
2. HAB authentication fails: Verify image signing
3. Kernel panic early: Check device tree compatibility
4. No boot media detected: Verify boot mode pins

Debug Tools

• UUU (Universal Update Utility): Flashing and recovery
• OpenOCD: JTAG debugging
• U-Boot console: Serial debug at 115200 baud
• Linux dmesg: Kernel boot messages

Resources

• NXP Official Documentation
• i.MX Linux Reference Manual
• U-Boot Documentation
• ARM Trusted Firmware

License

This documentation is provided for reference purposes. Refer to NXP official documentation for production use.

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*Last Updated: *
For NXP i.MX, Layerscape, and Kinetis Platforms