FIT images may be signed and verified by bootloader u-boot, as required for opencritis.org. FIT images may contain multiple images, such as the kernel, fdt device trees initramfs and scritps.

As the FIT image is tagging each embedded element, these entities are embedded in raw format, for example zImage, initrd.cpio and the scripts as simple text files. For example see this fit image declaration of file “image.its”

/dts-v1/;

/ {
  description = "OpenCritis arm/virt FIT Image";
  #address-cells = <1>;

  images {
          kernel {
             description = "Kernel";
             data = /incbin/("zImage");
             type = "kernel";
             arch = "arm";
             os = "linux";
             compression = "none";
             load = <0x40400000>;
             entry = <0x40400000>;
             hash {
                algo = "sha256";
             };
          };

          fdt {
            description = "Flattened Device tree";
            data = /incbin/("nxp6ulevk.dtb");
            type = "flat_dt";
            arch = "ARM";
            compression = "none";
            hash {
      	       algo = "sha256";
            };
        };
 
      bootscript {
        description = "Bootscript";
        data = /incbin/("u-boot.scr");
        type = "script";
        compression = "none";
      };           
};

configurations {
      default = "standard";
      standard {
            description = "Standard Boot";
            kernel = "kernel";
            fdt = "fdt";
            hash {
                    algo = "sha256";
            };
      };
   };
};     

An u-boot script “u-boot.scr” has the form:

setenv bootargs "console=ttyAMA0,115200 ro rootwait root=/dev/sda2"
bootm  ${loadaddr}
echo "Bad image or kernel."
reset

The fit image “image.ub” is generated using the following command

mkimage -f image.its image.ub 

Loading a fit image and sourcing the script is done as follows:

setenv loadaddr 0x48000000
fatload mmc 0:1  ${loadaddr} image.ub
source ${loadaddr}:bootscript

Note: indexed node names will be refused by u-boot FIT parser yielding “Bad FIT image format”, for example do not use the following form

...
script@1 { .... };