Based on information provided by "Allen Martin" <AMartin@nvidia.com>:

A hang is caused when the CPU generates a very fast CONNECT/HALT cycle
sequence.  Workaround is to set the SYSTEM_IDLE_TIMEOUT to 80 ns.
This allows the state-machine and timer to return to a proper state within
80 ns of the CONNECT and probe appearing together.  Since the CPU will not
issue another HALT within 80 ns of the initial HALT, the failure condition
is avoided.