U-boot stuck at Raspberry logo - Raspberry Pi Forums

i trying set raspberry pi b model boot u-boot, kernel on tftp , file system on nfs.
loads kernel tftp server see, after kernel started comes screen raspberry logo, nothing more happens.
have sd-card normal rasbian installation working fine hardware ok.
didn’t compile kernel myself copied kernel.img other sd-card tftp server
can't figure out wrong.
suggestions problem be?

i got little further on problem.
added u-boot existing working rasbian installation , loaded kernel tftp , part working, guess problem when tries mount nfs share file system.
other sd-card , tried booting see on nas (freenas 9.2.1.7) reports pi changed hardware address during boot.

seems between kernel load tftp , when mounts nfs share load file system pi changes hardware address, nas doesn’t update arp table pi inaccessible nas.

current uenv.txt

ipaddr=192.168.0.20
netmask=255.255.255.0
serverip=192.168.0.91
bootargs=console=ttyama0,115200 root=/dev/nfs rw nfsroot=192.168.0.91:mnt/storage1/raspberrypi1,tcp,vers3 rootwait ip=192.168.0.20:192.168.0.91:192.168.0.1:255.255.255.0:rpi:eth0:off rootfstype=nfs
bootcmd=usb start; dhcp ${kernel_addr_r} zimage; tftp ${fdt_addr_r} bcm2708-rpi-b.dtb; bootz ${kernel_addr_r} - ${fdt_addr_r};

raspberrypi