My i.mx6q mainboard is installed in a box and user can only access it with SD card and USB cable. It requires to update the linux image files on line which means user can not take the box apart. So all the boot mode pins and other cfg pins can not be accessed.
In normal operating, the system boots from emmc. How to implement this procedure:
connect USB to i.mx6 USB otg inteface(or insert a SD card with new image files) -> start to update new image files to emmc memory -> power off -> power on -> boot from emmc and go to normal operating.