Edge2 have advanced and flexible boot possibilities

SPL-loader ⇒ U-Boot-loader ⇒ OOWOW-special-mode ⇒ U-Boot-OS-boot-sequence ⇒ OOWOW-rescue-mode

• SPL-loader is a 1st boot-loader which can start from SPI-Flash ⇒ eMMC ⇒ SD card. By default its start from SPI-flash.
• SPL-loader scan special areas for next U-Boot-loader by SD ⇒ eMMC ⇒ SPI-FLash

spl-boot-example.log

U-Boot SPL board init
U-Boot SPL 2017.09 (Aug 26 2022 - 15:50:37)
MCU: bootmode: 1, oowow 0
board_boot_order: /chosen found, using spl_boot_device()
!!! same-as-spl: 
!!! /mmc@fe2c0000: 
!!! /mmc@fe2e0000: 
!!! /spi@fe2b0000/flash@1: 
Trying to boot from MMC2 :: 0
Card did not respond to voltage select!
Trying to boot from MMC1 :: 1
Trying fit image at 0x4000 sector
Not fit magic
Trying fit image at 0x5000 sector
Not fit magic
Trying to boot from MTD2 :: 2
Trying fit image at 0x300 sector
...

log spl-boot-oowow-mode-example.log

U-Boot SPL board init
U-Boot SPL 2017.09 (Aug 26 2022 - 15:50:37)
MCU: bootmode: 1, oowow 1
MCU: oowow 2
board_boot_order: /chosen found, using spl_boot_device()
!!! same-as-spl: 
+++ /spi@fe2b0000/flash@1: 
!!! /mmc@fe2c0000: 
!!! /mmc@fe2e0000: 
!!! /spi@fe2b0000/flash@1: 
Trying to boot from MTD2 :: 0
Trying fit image at 0x300 sector
...
Jumping to U-Boot(0x00200000) via ARM Trusted Firmware(0x00040000)
...

OS booting follow by distro_bootcmd which use boot_targets priority for scanning bootable OS.

kedge2# printenv boot_targets 
boot_targets=usb0 mmc1 mmc0 pxe dhcp fail