Making custom uSD from eMMC

HI,

I am using the SnapDragon board and I would need to make custom uSD.
I tried using dd but it doesn’t worked successfully…

I also tried making a bz2 of the whole rootfs but I noticed that the board rebooted automatically after a while…

Did you write have any automated tool to clone the eMMC content on a uSD ?
Thank you in advance,
s.