How to set the AM3715 processor operation speed into 800Mhz

Hi all,

I know AM3715 processor is  working in different operation speed like 300, 600,  800-MHz and 1Ghz.How can set operation speed into 800-Mhz in x-loader,u-boot and kernel.please help me any one as much as possible.

Thanks &Regards

Manjunath Goudar