[U-Boot] No single character output after update to latest u-boot on pandaboard

[Chao Xu]

Hi,

I'm trying to compile the latest u-boot for my Pandaboard Rev A2. The
SD card was originally loaded with a working version of 12.04
linaro-unbunt-developer image. Early printk is enabled in the original
image.

I followed this guide (http://elinux.org/Panda_How_to_MLO_%26_u-boot)
and here is what I did:
1. export ARCH=arm
2. export CROSS_COMPILE=arm-linux-gnueabi-
3. make omap4_panda_config
4.make
5. cp MLO u-boot.img /SDCARD/boot/

But when switching on my Panda, there is no output from the serial
port. And the heartbeat LED is always off. (When every thing works, it
is on when booting, and blinks after booting finished).

I don't have any former experience with u-boot. So please let me know
if there is any more info I should provide.

Any help would be much appreciated! Thank you!

-- 
Regards,
Chao Xu