Try these steps:
Getting the Pi 4 to NEMS 1.5.2 boot
If the Raspberry Pi has not been updated you will need to have a micro sd card flashed with Raspberry Pi OS to boot the pi and do updates. If Pi eeprom and firmware already updated skip
to Step 4. If unsure, continue.
1) Boot the Raspberry Pi from the microSD card with Raspberry Pi OS.
2) Open Terminal in Raspberry Pi OS (Note: you can do these steps from another computer via SSH if you want to set up the Pi headless).
3) Run the following commands:
sudo apt update
sudo apt full-upgrade
sudo rpi-eeprom-update -a
This should output something like:
:~ $ vcgencmd bootloader_version
Jul 16 2020 16:15:46
version 45291ce619884192a6622bef8948fb5151c2b456 (release)
**The date can be anything like July 16 2020 OR LATER!**
4) Open a terminal and run sudo raspi-config
5) Select 6 Advanced Options, Select A6 Boot Order, Select B1, select OK, Reboot
6) Shut down the Pi. Then unplug the microSD card.
7) On your PC, flash the NEMS image onto you choice of drive.
8) Before you eject the boot volume, you need to replace some files on it with the latest versions from GitHub. If flasher software auto ejected the drive, unplug and plug it back in
9) Go to the raspberrypi/firmware GitHub repository (https://github.com/raspberrypi/firmware
) and download the zip or clone the project to your computer (get the default master branch).
Or use this one-line command - https://gist.github.com/atomicstack/9c4 ... 8f65b0b1fa
- to just grab the necessary files without the entire repository.)
10) Inside the boot folder, copy over all the files that end in .elf or .dat to the boot volume of your NEMS drive (replace the same-named files that already exist there - it should
total about 22MB.
11) Eject the boot volume, and unplug the NEMS drive.
12) Plug your NEMS drive into you RPi
13) Power up the Pi, and after a coupple of minutes or so (it has to expand the USB drive to fill the volume and then reboot), it should boot up!