As we know, if we want to burn sd card in uboot, first we should use command line :
tftp a0000000 firmware_<machine>_uboot_sdboot.img
then we will use command
mmc write a0000000 8 1f000 to burn it.
So my question is why the start block is 8?, Is the first 8 block is for RCW binary and PBL? So I think that we had burned a U-boot image before if we use this command?