power - power button and power fail support
power0 at mainbus?
HP PA-RISC machines support power failure detection in different forms:
+o ``soft'' power button
+o power failure interrupt
The power driver tries its best to determine the power failure condition
that is a result of a power button being depressed or a power supply system
failure or a similar condition. Upon detection of any
of the aforementioned
conditions, it tries to gracefully (if possible)
shutdown the
system through a call to the boot(9) function.
On systems equipped with the lasi(4) bus adapter, we find a
``soft'' power
button which upon depression gives us a signal in the
``power
register'' and thus polling periodically we detect the
event. Since that
bit comes directly from the power button without any dampening, we perform
a second long delay; thus quick transitions off and on
will not result
in a shutdown.
On modern systems, an interruption is signalled upon the
power button depression
and thus this avoids polling and does not require
(as does being
implemented in hardware) dampening.
intro(4), lasi(4), boot(9)
The power driver appeared in OpenBSD 3.4.
OpenBSD 3.6 August 20, 2003
[ Back ] | 