I am using this Android 4.2 NAND image with my Marsboard A20. The HDMI output is working fine but there is some underscan (black borders around the screen). The image has busybox and rooting pre-installed.

I've found here i need to edit uEnv.txt in order to fix it. Btw, trying to mount the boot partition like this fails:

mkdir /boot
mount /dev/block/mmcblk0p1 /boot
  • What resolution does your Marsboard A20 hasve and what your screen? They seem to use different ones, thus the screen adds black borders where the screen region doesn't fit.
    – GiantTree
    Feb 14, 2015 at 13:14
  • The Android image is set for 720p, while my LCD has a native resolution of 1080p. I've also tried the build set for 1080p and the screen was cropped instead (i could not see a part of it)
    – eadmaster
    Feb 14, 2015 at 15:17
  • Then your "720p" has probably a different aspect ratio (16:10 instead of your LCD having 16:9) therefore you get those black borders.
    – GiantTree
    Feb 14, 2015 at 15:23

1 Answer 1


Your question is a bit misleading because what you really need to know is how to modify a file inside the boot partition.

Your mount issue is probably there because the boot partition is running from a rootfs image contained in the kernel image and not directly from the mmc-device. You will have to unpack, modify and repack it, but probably it will get easier if you

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