[U-Boot] Using u-boot with qemu-system-mips(qemu-2.1.2) caused infinite loop

[jiang]

Hello all:
I just downloaded the latest u-boot source code,then compiled with:
make qemu_mips_defconfig
make CROSS_COMPILE=mips-linux-uclibc-
then create image:
# dd of=flash bs=1k count=4k if=/dev/zero
# dd of=flash bs=1k conv=notrunc if=u-boot.bin

run with:
qemu-system-mips -M mips -pflash flash -nographic

but I got nothing then I try to debug with gdb,I got this:

0xbfc001fc <_start+508>:    nop
0xbfc00200 <_start+512>:    b    0xbfc00200 <_start+512>
0xbfc00204 <_start+516>:    nop
0xbfc00208 <_start+520>:    nop

Another thing, the file u-boot.bin I got was 215k, is that ok?

What should I do to use u-boot in qemu?:)