POWER(4) | Device Drivers 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:

- “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.

# SEE ALSO

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

# HISTORY

The `power` driver appeared in OpenBSD 3.4.

May 31, 2007 | Debian