If you want to use the i.MX6 signed security boot image by uuu(usb download).
You need to follow the steps in uuu.pdf.
The reason is clear in the uuu.pdf.
My understanding is
Because in usb download, the IVT will download first not entire image(here is uboot). So, it should be authenticated first.
uuu.pdf.
Since the IVT is modified when downloading to the target the binary must be signed with a cleared DCD pointer. However, the binary must be provided with a valid DCD pointer to allow the UUU tool to locate the DCD table.
A. The steps below can be used as an examp
$ ./mod_4_mfgtool.sh clear_dcd_addr u-boot-dtb.imx
$ ./cst --i u-boot-csf.txt --o u-boot-csf.bin
$ ./mod_4_mfgtool.sh set_dcd_addr u-boot-dtb.imx
You when you use the uuu to do download, you need two security image, one is output by "A"
Another is the image as you said " convientional way to sign". to flash to like emmc, for example.
uuu -b emmc u-boot.uuu.use u-boot
u-boot.uuu.use --- from A
u-boot --- you said " convientional way to sign"