![]() Their location has already been determined earlier.Īfter parsing config.txt, commonly start4.elf and other related boot files are downloaded and executed. This file only determines which files are loaded, not from where they are retrieved. This file determines which boot files will be downloaded next, and can freely be configured by the Linux distribution or the user. The first file that is actually downloaded is config.txt. If it fails to detect start4.elf in its own directory, the Pi will attempt to get the boot files from the root directory of the TFTP server instead. This function allows each Pi in the same network to have its own boot files. If the TFTP server reports that start4.elf exists in this directory, all other boot files will also be loaded from the same directory. While connecting to the TFTP server, the Pi 4B will first attempt to get start4.elf from a directory based on the Pi’s serial number, the embedded Ethernet controller’s MAC address or a custom value, depending on the configuration in bootconf.txt contained in the EEPROM. When booting from network, all necessary network configuration parameters can either be provided through DHCP (as with previous Pi models) or in the early boot configuration contained in the EEPROM. Check out this page for the last beta version. Newer versions have been released since then that fix bugs. A beta version of the EEPROM boot code was released on 23 September 2019 which allows a Pi 4B to load the necesary files either from an SD card or from a TFTP server using the embedded Ethernet controller. Fortunately, the EEPROM can be reprogrammed with newer boot code released by the Raspberry Pi Foundation. All current Pi 4B computers were shipped with EEPROM boot code that can only load the necessary files from an SD card. The purpose of the EEPROM boot code is to load and execute the next boot stage contained in start4.elf. The early boot configuration (bootconf.txt).Note that the Pi 4B does not use bootcode.bin. A proprietary binary blob, similar to bootcode.bin for the older Raspberry Pi models. ![]() The EEPROM contains 512 KiB of boot code that is executed after the ROM code is executed. The system on chip (SoC) of the Pi 4B is the BCM2711B0, which contains an embedded EEPROM. It is after executing the code in ROM that the new boot process differs. Some non-critical boot files are not mentioned, such as fixup4.dat (used for shared memory management between the GPU and CPU).Īs noted in the older article, a Pi’s boot process always starts with the graphical processing unit (GPU) running proprietary code from ROM. A few liberties were taken to simplify the drawing. However, some preparation of the Pi 4B might be necessary, depending on its age.Ī typical Raspberry Pi 4 network boot is shown in the above figure. It is possible to network boot a Raspberry Pi 4 Model B (Pi 4B) without an SD card. This post does contain an up-to-date DHCP server configuration which can also be used to boot older Pi models in addition to the Pi 4B. Some parts were taken from my previous post concerning network booting older Raspberry Pi models. What is written here is based on this page from the Raspberry Pi Foundation and on my own findings. The new boot process will be explained, and a configuration will be offered that will allow network booting of both older and newer Raspberry Pis in a single network. The new boot procedure of the Pi 4B is unlike its predecessors, and this warrants a new post. I did this earlier for older Raspberry Pi models. In this post I explain the ins and outs of network booting a Raspberry Pi 4 Model B (Pi 4B).
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