If an exception is caused while executing code within the exception
handler, the NMI handler, the reset vector, or in emulator mode,
a double fault occurs. On the Blackfin, this is a unrecoverable
event. You have two options:
- RESET exactly when double fault occurs. The excepting
instruction address is stored in RETX, where the next kernel
boot will print it out.
- Print debug message. This is much more error prone, although
easier to handle. It is error prone since:
- The excepting instruction is not committed.
- All writebacks from the instruction are prevented.
- The generated exception is not taken.
- The EXCAUSE field is updated with an unrecoverable event
The only way to check this is to see if EXCAUSE contains the
unrecoverable event value at every exception return. By selecting
this option, you are skipping over the faulting instruction, and
hoping things stay together enough to print out a debug message.

This does add a little kernel code, but is the only method to debug
double faults - if unsure say "Y"