AM1808 silicon version 2.1 boot from SD card

Hi 

    We have custom board of OMAP l138 custom board. We populated the two board one is with OMAP l138 chip another one is with AM1808B chip (version 2.1) but both are same schematics no changes in schematic just difference chip. 

OMAP l-138 boot successfully from SD card there is no issue and boot switch setting is high BOOT[4] 

I'm using same SD card with same boot switch on AM1808 board but its not booting there is blank terminal page. 

version details are

AM1808B ZWT chip here "B" denotes silicon revision 2.0 or 2.1 

TI-SDK version : ti-sdk-omapl138-lcdk-01.00.00 

Linux version   :  linux-3.1.10

u-boot version :  u-boot-2010.12-psp03.21.00.04.lcdk

Where is the problem 

1. Do we need to change the boot switch for AM1808 boot from SD card ?

2. Do we need to use any other version of u-boot or PSP ?

3. Do we need to do any hardware changes ?

Please let me know the issue for boot from SD card.

Thanks

Sangily.