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Add hint about how to build an ISA NMI card and why you'd want to do so.

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Reviewed by: bde, dima dorfman
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Warner Losh 2001-05-02 03:26:10 +00:00
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share/man/man4/ddb.4
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@ -522,6 +522,18 @@ indirection. It may be followed by a
.Sq Li :
and modifiers as described above.
.El
.Sh HINTS
On machines with an ISA expansion bus, a simple NMI generation card can be
constructed by connecting a push button between the A01 and B01 (CHCHK# and
GND) card fingers.
Momentarily shorting these two fingers together may cause the bridge chipset to
generate an NMI, which causes the kernel to pass control to
.Nm .
Some bridge chipsets do not generate a NMI on CHCHK#, so your mileage may vary.
The NMI allows one to break into the debugger on a wedged machine to
diagnose problems.
Other bus' bridge chipsets may be able to generate NMI using bus specific
methods.
.Sh SEE ALSO
.Xr gdb 1
.Sh HISTORY