u-boot reads both /boot/uEnv.txt and /uEnv.txt anyway. However, not sure whether its a bug or a feature, certain things, e.g. uenvcmd don't work if they are not in /uEnv.txt.One thing that confuses me is does /boot/uEnv.txt refer to uEnv.txt in a /boot directory of the FAT partition or is the FAT partition regarded as /boot.