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.\" LP (Laptop Package)
.\"
.\" Copyright (c) 1994 by HOSOKAWA, Tatsumi <hosokawa@mt.cs.keio.ac.jp>
.\"
.\" This software may be used, modified, copied, and distributed, in
.\" both source and binary form provided that the above copyright and
.\" these terms are retained. Under no circumstances is the author
.\" responsible for the proper functioning of this software, nor does
.\" the author assume any responsibility for damages incurred with its
.\" use.
.Dd November 1, 1994
.Dt APM 4
.Os
.Sh NAME
.Nm apm
.Nd APM BIOS interface
.Sh SYNOPSIS
.Cd options APM
.Cd device apm0 at isa?
.Sh DESCRIPTION
.Nm apm
is an interface to the Intel / Microsoft APM (Advanced Power Management) BIOS
on laptop PCs.
.Pp
.Nm apm
provides the following power management functions.
.Bl -enum -offset indent
.It
When the system wakes up from suspended mode,
.Nm apm
adjusts the system clock to RTC.
.It
When the system wakes up from suspended mode,
.Nm apm
passes a message to
.Xr syslogd 8
comprising of system wakeup time and elapsed time during suspended mode.
.It
.Nm apm
slows CPU clock when there are no system activities (runnable processes,
interrupts, etc.). This function is available only on systems whose APM
supports CPU idling.
.It
.Nm apm
exports an application interface as a character device. Applications
can control APM, or retrieve APM status information via this interface.
.Nm apm
exports the following interfaces. These symbols are defined in
.Dq Pa /usr/include/machine/apm_bios.h.
.Bl -tag -width 4n -offset indent
.It Sy APMIO_SUSPEND
Suspend system.
.It Sy APMIO_GET
Get power management information.
.It Sy APMIO_ENABLE
.It Sy APMIO_DISABLE
Enable / Disable power management.
.It Sy APMIO_HALTCPU
.It Sy APMIO_NOTHALTCPU
Control execution of HLT in the kernel context switch routine.
.Pp
Some APM implementations execute the HLT
.Pq Halt CPU until an interrupt occurs
instruction in the
.Dq Pa Idle CPU
call, while others do not. Thus enabling this may result in
redundant HLT executions because
.Dq Pa Idle CPU
is called from the kernel context switch routine that inherently executes
HLT. This may reduce peak system performance.
.Pp
Also the system hangs up if HLT instruction is disabled in the kernel
context switch routine, and if the APM implementation of the machine
does not execute HLT in
.Dq Pa Idle CPU.
On some implementations that do not support CPU clock slowdown, APM
might not execute HLT.
.Nm apm
disables
.Sy APMIO_NOTHALTCPU
operation on such machines.
.Pp
The current version of
.Nm apm
does not call
.Dq Pa Idle CPU
from the kernel context switch routine if clock slowdown is not supported,
and it executes HLT instruction by default. Therefore, there is
no need to use these two operations in most cases.
.El
.Pp
These interfaces are used by
.Xr apm 8
and
.Xr apmconf 8 .
.It
.Nm apm
polls APM events and handles the following events.
.Bl -column PMEV_POWERSTATECHANGEXXX "suspend system xxxxx"
.It Sy "Name " "Action " "Description"
.It Dv "PMEV_STANDBYREQ " No "suspend system " "standby request"
.It Dv "PMEV_SUSPENDREQ " No "suspend system " "suspend request"
.It Dv "PMEV_USERSUSPENDREQ " No "suspend system " "user suspend request"
.It Dv "PMEV_CRITSUSPEND " No "suspend system " "critical suspend request"
.It Dv "PMEV_NORMRESUME " No "resume system " "normal resume"
.It Dv "PMEV_CRITRESUME " No "resume system " "critical resume"
.It Dv "PMEV_STANDBYRESUME " No "resume system " "standby resume"
.It Dv "PMEV_BATTERYLOW " No "notify message " "battery low"
.It Dv "PMEV_UPDATETIME " No "adjust clock " "update time"
.El
.El
.Sh BUGS
WARNING! Many, if not most, of the implementations of APM-bios in laptops
today are buggy. You may be putting your LCD-display and batteries at
a risk by using this interface. (The reason this isn't a problem for
MS-windows is that they use the real-mode interface.) If you see any
weird behaviour from your system with this code in use, unplug the
power and batteries ASAP, if not imidiately, and disable this code.
.Pp
We are very interested in getting this code working, so please send you
observations of any anormalous behaviour to us.
.Pp
When
.Nm apm
is active, calling the BIOS setup routine by using hotkeys,
may cause serious trouble when resuming the system.
BIOS setup programs should be called during bootstrap, or from DOS.
.Pp
Some APM implementations cannot handle events such as pushing the
power button or closing the cover. On such implementations, the system
.Ar must
be suspended
.Ar only
by using
.Xr apm 8
or
.Xr zzz 8 .
.Pp
Disk spindown, LCD backlight control, and power on demand have not
been supported on the current version.
.Sh SEE ALSO
.Xr apm 8 ,
.Xr zzz 8 ,
.Xr apmconf 8
.Sh AUTHOR
HOSOKAWA, Tatsumi <hosokawa@mt.cs.keio.ac.jp> (Keio Univ., Japan)
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