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NAME    [Toc]    [Back]

     power - power button and power fail support

SYNOPSIS    [Toc]    [Back]

     power0 at mainbus?

DESCRIPTION    [Toc]    [Back]

     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
     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.

SEE ALSO    [Toc]    [Back]

     intro(4), lasi(4), boot(9)

HISTORY    [Toc]    [Back]

     The power driver appeared in OpenBSD 3.4.

OpenBSD     3.6                         August      20,      2003
[ Back ]
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