[quote user="sreejaya varma"] But I was not able to clock the CPU above 360MHz without mentioned DDR2 issue.[/quote]
I don't understand the connection here... The CPU is clocked by PLL0 and the DDR2 is clocked by PLL1. Changing the frequency on one should not affect the other. The DDR2 max frequency is 156 MHz. You should be able to change the CPU frequency at will and not have any effect whatsoever on the DDR2. If increasing the frequency of the CPU above 360 MHz is causing an issue then it sounds to me like you have a power issue related to the CPU rail. In particular you should make sure you're supplying the proper voltage and have sufficient decoupling caps.