I found a little problem in cpu/mpc8xx/cpu_init.c in u-boot-1.2.0. There are some instructions to reset br0 for MPC850 near line 120. This code is executed for all cpu. In my opinion should be limited to MPC850 cpu because, after a few lines when br0 is configured with CFG_BR0_PRELIM, debuggers (like BDI) receive a machine check exception. It seems that resetting BR0 and setting it again causes some debugging problems.