Below is the layout for sd card booting. Remember to use

dd if=spl/sunxi-spl.bin of=/dev/sdX bs=1024 seek=8 ; dd if=u-boot.bin of=/dev/sdX bs=1024 seek=32

to flash spl & u-boot into sd card

sector start size 

0    0   8KB   Unused, available for partition table etc. 

16   8   32KB  Initial SPL loader 

80   40  504KB u-boot (sector 64 / 32KB for 2013.07 and earlier) 

1088 544 128KB environment 

1344 672 128KB Falcon mode boot params 

1600 800 —-  Falcon mode kernel start 

2048 1024 –    Free for partitions (higher if using Falcon boot)