AM3352-SOM rev C cannot boot after power cycle

[bytebird]

Hi,
We have standalone AM3352-SOM (rev C) powered by 5V supply through the debug port. No EVB board is connected. We used prebuild image from your website:  AM3352-SOM Debian image with kernel 3.12.10+ release 4.
The first time bootup normally went through smoothly. The board refuses to boot after power cycle. U-Boot stopped at sdram_init. See the following debug port output. Please advise solution.

Thanks

get_dpll_ddr_params
set_mux_conf_regs
--DEBUG-- Configuring i2c1 pinmux
--DEBUG-- Configuring mii1 pinmux
--DEBUG-- Configuring mmc0 pinmux
--DEBUG-- Configuring mmc1 pinmux
sdram_init