SIR is a Software Initiated Reset.  I sprinkled some of those throughout 
   locore.s primarily for diagnostic reasons in places where the machine 
   state gets so stuffed up that it can't recover.
   
   To find out what's really happening, after you get the SIR you need to 
   type `.trap-registers' and write down the TPC values.  Then boot the 
   kernel and see which TPC points to an SIR instruction.  Then correlate 
   that with the code in locore.s and look at the comments around the SIR to 
   determine what really went wrong.


additionally, sometimes these SIR's are not in the kernel but in OFW.