I Completed booting armstrong image into beagleboard-xm.
and then i want to connect this kit to another hard ware for accessing that hardware pherirals using UART or other if it .
how it will do.
BB-XM has 1.8V voltage level for IO, but Atmega can support either 3.3V or 5V. You can get a USB-Uart cable and connect a USB part to XM, UART part to Atmega. Enjoy