power —
power button and power fail support
power0 at mainbus?
HP PA-RISC machines support power failure detection in different forms:
- “soft” power button
- 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),
pdc(4),
boot(9)
The
power driver appeared in
OpenBSD 3.4.
![[OpenBSD]](/openbsd.gif){kind=small}