PiSetup
Pi 4: netboot is disabled by default, and you need to flash a config that enables it
https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#BOOT_ORDER
the BOOT_ORDER field tells it what things it can boot from, and in what order to check them youll need a 2 in there for it to netboot it is possible to create an SD card from an x86 system, that will re-flash the pi4 with your desired config
https://gist.github.com/cleverca22/b50adb85384f94979f15b6572ad20d64 rpi4 self reflashing
https://github.com/raspberrypi/rpi-eeprom raspberrypi/rpi-eeprom: Installation scripts and binaries for the closed sourced Raspberry Pi 4 EEPROMs
rpi-eeprom-config --edit, and set BOOT_UART=1
you use the rpi-eeprom-config (python script) from here to embed a bootconf.txt into a firmware version of your choice, then you pop pieeprom.bin, pieeprom.sig, and recovery.bin onto an SD card, and boot it
if you name the file pieeprom.bin, then it will flash, verify, display red/green on the hdmi, and hang
if you instead name it pieeprom.upd, it will verify, rename recovery.bin and reboot, causing whatever OS is on the card to boot normally
pieeprom.bin is better for a reusable card to bulk-flash many devices
pieeprom.upd is more for an os to re-flash the firmware on the current pi
details: https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#network-boot-flow
