Start up your board. Use uuu to supply it with a valid firmware image package:

uuu -b spl flash.bin

Connect to the serial cable (the DEBUG one), then open a terminal (recall: /dev/ttyACM0 on Linux – usually!), e.g. using picocom (don't forget to set baudrate to 115200!) and power on the board via the USB-C cable!

First things first: let's check if the flashing process was succesful. Reload your FIP using uuu and get back into the U-Boot shell.

u-boot=> # list MMC devices (or rather, the slots)
u-boot=> mmc list
FSL_SDHC: 0 (eMMC)
FSL_SDHC: 1

u-boot=> # select MMC device 0
u-boot=> mmc dev 0
switch to partitions #0, OK
mmc0(part 0) is current device

u-boot=> # show partitions on currently selected MMC device
u-boot=> mmc part

Partition Map for MMC device 0  --   Partition Type: DOS

Part    Start Sector    Num Sectors     UUID            Type
  1     20480           184320          5a0f642d-01     83
  
u-boot=> # show contents of / directory on MMC device 0, partition 1
u-boot=> # assuming that the partition in question is FAT
u-boot=> fatls mmc 0:1
 72709475   linux.itb

1 file(s), 0 dir(s)

In order for U-Boot to parse the FIT image and extract its components at their respective load addresses, we first need to bring the entire FIT image in main memory (use the load or fatload command for this). Choose a load address where the FIT image will not overlap with any of the three components when unpacked, or with the relocated bl33 code, e.g. >= 0x90000000.

This step is optional, but gives us the chance to see how U-Boot can parse a DTB file and extract its information. In the following example we assume that you've loaded the FIT image at address 0x81000000 (i.e.: 64MB offset in DRAM):

u-boot=> # mark 0x80000000 as the starting address of a device tree
u-boot=> fdt addr 0x90000000

u-boot=> # show contents of specific nodes in the RAM-based DTB
u-boot=> fdt list /
/ {
        timestamp = <0x64b55028>;
        description = "Linux FIT image for FRDM iMX93";
        #address-cells = <0x00000001>;
        images {
        };
        configurations {
        };
};

u-boot=> fdt list /configurations
configurations {
        default = "normal-boot";
        normal-boot {
        };
};

u-boot=> fdt list /configurations/normal-boot
normal-boot {
        description = "Normal boot config";
        kernel = "kernel";
        fdt = "fdt";
        ramdisk = "initrd";
};

Use the bootm <loaded_fdt_address> command, passing it the starting address of the FIT image.

Linux should start displaying kernel messages!