I did not get into hardware circuitry of Wand-board Dual. Advance Apologies for that.
Up to my knowledge U boot SPL( secondary program loader) will be used to load full fledged U boot when there is little memory and is not sufficient to load full fledged boot loader at initial stage itself.
But as per this page.
[type or paste code here](https://forum.digikey.com/t/debian-getting-started-with-the-wandboard/12707)
All the Uboot.spl, uboot.img, kernel, rootfs are flashed in the same SD card and the board has 1GB of ram.
Please clarify my doubt why in this case spl and also main uboot.img both are needed.