OMAP-L138: At which point is the DDR2 memory controller set up?

The OMAP-L138 can set a number of DDR2 registers - we have used AISGEN generated files to set this as part of the U-boot loader and we can see the values taken effect in the SYSTEM memory locations of the OMAP

My question is - is the AIS path the only way to set these registers or is there another way to set the registers.

or is the DDR2 configuration done at power-up only ?

In particular we would like to increase the refresh rate.

b.