Made by ChatGPT

1. Raspberry Pi Boot
Mechanism Overview
Understanding booting blobs between U-Boot and Linux
Masafumi Ohta
Japanese Raspberry Pi Users Group
(by ChatGPT)

2. Raspberry Pi Boot Stages (Pi 4/5)
• 1. ROM Code (SoC): Starts on GPU, loads EEPROM or
bootcode.bin
• 2. bootcode.bin / EEPROM: Initializes RAM and loads
firmware
• 3. start4.elf: GPU firmware loads config.txt and next file
• 4. u-boot.bin or kernel8.img: Either U-Boot or Linux directly
• 5. U-Boot (optional): Loads kernel, DTB, and initramfs
• 6. Linux Kernel: Takes over and starts init process

3. U-Boot to Linux Transition
• config.txt sets kernel=u-boot.bin
• U-Boot loads Image, *.dtb, and initramfs
• Executes booti or bootm to start Linux
• Passes control with memory addresses

4. Booting Blobs of Interest
• start4.elf: GPU firmware (proprietary)
• u-boot.bin: ARM64 bootloader
• Image: Linux kernel binary
• *.dtb: Device Tree Blob
• initramfs: Optional initial RAM filesystem

5. Sample config.txt and U-Boot Script
• [config.txt]
• enable_uart=1
• kernel=u-boot.bin
• arm_64bit=1
• [U-Boot script]
• load mmc 0:1 0x80000 Image
• load mmc 0:1 0x200000 *.dtb
• booti 0x80000 - 0x200000

6. Tools to Analyze Boot Components
• dtc: Compile/decompile device trees
• file: Detect binary formats
• readelf, objdump: Inspect kernel/U-Boot
• hexdump, xxd: View hex contents
• strings: Extract readable text from binaries