-This version of U-BOOT doesn't implement SPL but it is required(BL2)
-and can be found in "boot.tar.gz" from here:
+This version of U-BOOT doesn't implement SPL. So, BL1, BL2, and TrustZone
+binaries are needed to boot up.
+
+<< X2/U3 >>
+It can be found in "boot.tar.gz" from here: