Is there any documentation available for setting up bootcode.bin to boot a USB hard disk? When I tried a few days ago, boot went straight to network, not seeing the USB disk at all. It's an older Pi3B, with a powered USB hub and a USB3-SATA disk enclosure using a Jmicron controller. The same type of disk and controller boots a Pi4 hands off, so I _think_ the Pi3 is the problem, not the disk.
If I interrupt the normal u-boot via the serial console and run a few cycles of usb reset eventually the disk shows up, at that point using the run bootcmd_usb0 command works to boot from the disk.
Adding a timeout file and putting program_usb_boot_timeout=1 in config.txt didn't seem to make any consistent difference. Setting usb_pgood_delay in u-boot's environment might have helped a little, but I'm not sure that was working correctly because the saveenv command caused a "write to FAT failed" message.
Thanks for reading,
bob prohaska