[U-Boot-Users] where to modify my system clock in a tqm8xxl model?

hello,all
   Congratulations on the release of the u-boot-1.0.0!Can you tell me 
where to set the system clock in a tqm8xxl model?  My hyperteminal has 
displayed this (there are some "printf" added):

U-Boot 0.4.8 (Oct 31 2003 - 15:47:15)

gd->cpu_clk=25000000
immr=0xff002101
pvr=0x500000
CPU:   XPC823xxZTnnB2 at 25 MHz: 2 kB I-Cache 1 kB D-Cache
Board: WindRiver mdppro8xx
DRAM:  16 MB
before relocate_code()

  Now I want to set my system clock to 50MHz,but I don't know how to 
modify,which file should I modify?I know the gd->cpu_clk is initialized 
in cpu/mpc8xx/speed.c.
  Thank you for your time!