The Pi4 with the BCM2711 SoC has a new, more sophisticated boot process. The addition of an EEPROM means that the
bootcode.bin file found in
/boot is no longer required. Details of the EEPROM can be found here.
The boot flow for the Pi4 is as follows:
- BCM2711 SoC powers up
- On board bootrom checks for bootloader recovery file (recovery.bin) on the SD card. If found, it executes it to flash the EEPROM and recovery.bin triggers a reset.
- Otherwise, the bootrom loads the main bootloader from the EEPROM.
- Bootloader checks it's inbuilt BOOT_ORDER configuration item to determine what type of boot to do.
- SD Card
- USB mass storage
SD Card Boot
Details of the network booting can be found here
USB mass storage boot
USB booting is still under development.
BOOT_ORDER configuration item is embedded inside the bootloader code in the EEPROM. See the Pi4 Bootloader Configuration page for details on how to change the bootloader configuration.