Turns out I created a wrong program which caused an infinite loop of boot&resetting of u-boot, hence the "slow blinking" occured. It should be U-BOOT + OpenWRT.bin + some paddings + ART, I make a mistake on the order of firware partition & art partition.
However, when I use serial port to find the problem, I saw u-boot only recognize 4M flash, Does this mean I need modify the u-boot source code like this thread?
U-Boot 1.1.4 (Apr 15 2013 - 16:30:28)
AP93 (ar7240) U-boot
DRAM:
sri
#### TAP VALUE 1 = 8, 2 = 8
32 MB
id read 0x100000ff
flash size 4194304, sector count = 64
Flash: 4 MB
Using default environment
BOARD IS NOT CALIBRATED!!!
In: serial
Out: serial
Err: serial
Net: ag7240_enet_initialize...
No valid address in Flash. Using fixed address
: cfg1 0xf cfg2 0x7014
eth0: 00:03:7f:09:0b:ad
eth0 up
No valid address in Flash. Using fixed address
: cfg1 0xf cfg2 0x7214
eth1: 00:03:7f:09:0b:ad
ATHRS26: resetting s26
ATHRS26: s26 reset done
eth1 up
eth0, eth1
Autobooting in 1 seconds
## Booting image at 9f020000 ...
Uncompressing Kernel Image ... Error: Bad gzipped data
GUNZIP ERROR - must RESET board to recover
Resetting...
(** infinite loop from the begining **)
^
|---- I use U-Boot to upgraded to a new U-Boot with Web Failsafe, then use the new U-Boot fixed/upgraded the firmware and art, now everything is ok.
(Last edited by lovetide on 25 Nov 2014, 12:43)