how to change the alt_timestamp counter size to 64 bit

The default counter size for alt_timestamp() is 32 bit and the counter will overflow when it reaches count beyond 2^32.

How do i change it to count up to 64 bit? I have changed both the system clock timer core and timestamp timer core counter size to 64 bit in the SOPC builder and regenerated the whole system.

What else do i have to modify? Do i have to modify the h headers?

Thanks.