traps, so that ddb can keep control (almost) no matter how it is
entered. This breaks time-critical interrupts while the system is
stopped in ddb, but I haven't noticed any significant problems except
that applications become confused about the time. Lost time will be
adjusted for later. Anyway, the half-baked disabling of interrupts in
Debugger() gives the same problems for the usual way of entering ddb.
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