[casper] Fault led and power cycling of roach2

[Kim Guzzino]

Hello all,
   We are having problems with our Roach 2 and don't want to update the
Borph/uboot yet. Occasionally we get a fault light and our fpga will not
run until we power down (by pulling the plug) and then up. If we cycle
power with the power button the fault light remains, even after loading
the bof. 
  Question, under what conditions is the fault light driven?
That' it.
Kim