u-boot-related but maybe off-topic question

Ehm... first of all I want to beg for pardon for posting this maybe rather off-topic question.

It's just that I'm not sure about how to program the memory controller of my MPC875 in the u-boot:

Though it seems possible to issue only one refresh command each time the memory refresh timer expires, it seems to be common to have the refresh-timer expire more seldom and issue more refresh-commands in a row each time to compensate for this.
Issuing a refresh-command is only possible in "all banks precharge" state, the sdram memory datasheet says. So what I need to know is: Which operations cause a memory bank to be "un-pre-charged"? I can't find that information anywhere, it's like it's so trivial that noone mentions it.

Thanks for your time,

Peter Asemann