My PBP starts up like a 1977 Chevy Nova
Uboot will ONLY be found on SPI or emmc or SD
(the boot on usb, from bootrom, is ONLY to write code to SPI, all media MUST be removed or disabled to get this boot)
Once uboot loads from one of those 3 places, then uboot is in charge of the boot
It (uboot) can and does change the boot order and can ALSO boot from network as well as usb
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strings uboot.img |grep -i _target
boot_targets=mmc1 nvme0 usb0 mmc0 pxe dhcp
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Unless you are using tow-boot uboot version, you will not get a boot with a SD card in an adapter
Try writing to a usb stick, do try BOTH sockets, I have seen it nearly always ignore one and boot from other
(the boot on usb, from bootrom, is ONLY to write code to SPI, all media MUST be removed or disabled to get this boot)
Once uboot loads from one of those 3 places, then uboot is in charge of the boot
It (uboot) can and does change the boot order and can ALSO boot from network as well as usb
-----
strings uboot.img |grep -i _target
boot_targets=mmc1 nvme0 usb0 mmc0 pxe dhcp
-------
Unless you are using tow-boot uboot version, you will not get a boot with a SD card in an adapter
Try writing to a usb stick, do try BOTH sockets, I have seen it nearly always ignore one and boot from other