Problem getting machine check reset on 8245

I implemented do_reset in Linux 2.6 using the
reset method of U-Boot -- turn off the MMU and write
to an invalid address.  Sometimes I the desired reboot.
If I change the code a bit (e.g. put a 'nop' just ahead
of turning off the MMU), I'll get an "Invalid floating
point instruction" exception.  How is that possible??
I didn't thing printk shouldn't would work if the MMU is turned off.
Has anybody seen anything like this?? Thanks!