POWER(4)              OpenBSD Programmer's Manual (HPPA)              POWER(4)

NAME
     power - power button and power fail support

SYNOPSIS
     power0 at mainbus?

DESCRIPTION
     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 sys-
     tem failure or a similar condition.  Upon detection of any of the afore-
     mentioned 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'' pow-
     er 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 per-
     form a second long delay; thus quick transitions off and on will not re-
     sult in a shutdown.

     On modern systems, an interruption is signalled upon the power button de-
     pression and thus this avoids polling and does not require (as does being
     implemented in hardware) dampening.

SEE ALSO
     intro(4), lasi(4), pdc(4), boot(9)

HISTORY
     The power driver appeared in OpenBSD 3.4.

OpenBSD 4.7                      May 31, 2007                                1
