146 lines
4.7 KiB
Groff
146 lines
4.7 KiB
Groff
.\" LP (Laptop Package)
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.\"
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.\" Copyright (c) 1994 by HOSOKAWA, Tatsumi <hosokawa@mt.cs.keio.ac.jp>
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.\"
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.\" This software may be used, modified, copied, and distributed, in
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.\" both source and binary form provided that the above copyright and
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.\" these terms are retained. Under no circumstances is the author
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.\" responsible for the proper functioning of this software, nor does
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.\" the author assume any responsibility for damages incurred with its
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.\" use.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd November 1, 1994
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.Dt APM 4 i386
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.Os
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.Sh NAME
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.Nm apm
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.Nd APM BIOS interface
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.Sh SYNOPSIS
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.Cd device apm0 at nexus?
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.Sh DESCRIPTION
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.Nm apm
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is an interface to the Intel / Microsoft APM (Advanced Power Management) BIOS
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on laptop PCs.
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.Pp
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.Nm apm
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provides the following power management functions.
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.Bl -enum -offset indent
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.It
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When the system wakes up from suspended mode,
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.Nm apm
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adjusts the system clock to RTC.
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.It
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When the system wakes up from suspended mode,
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.Nm apm
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passes a message to
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.Xr syslogd 8
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comprising of system wakeup time and elapsed time during suspended mode.
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.It
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.Nm apm
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slows CPU clock when there are no system activities (runnable processes,
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interrupts, etc.). This function is available only on systems whose APM
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supports CPU idling.
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.It
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.Nm apm
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exports an application interface as a character device. Applications
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can control APM, or retrieve APM status information via this interface.
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.Nm apm
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exports the following interfaces. These symbols are defined in
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.Dq Pa /usr/include/machine/apm_bios.h.
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.Bl -tag -width 4n -offset indent
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.It Sy APMIO_SUSPEND
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Suspend system.
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.It Sy APMIO_GET
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Get power management information.
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.It Sy APMIO_ENABLE
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.It Sy APMIO_DISABLE
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Enable / Disable power management.
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.It Sy APMIO_HALTCPU
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.It Sy APMIO_NOTHALTCPU
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Control execution of HLT in the kernel context switch routine.
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.Pp
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Some APM implementations execute the HLT
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.Pq Halt CPU until an interrupt occurs
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instruction in the
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.Dq Pa Idle CPU
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call, while others do not. Thus enabling this may result in
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redundant HLT executions because
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.Dq Pa Idle CPU
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is called from the kernel context switch routine that inherently executes
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HLT. This may reduce peak system performance.
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.Pp
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Also the system hangs up if HLT instruction is disabled in the kernel
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context switch routine, and if the APM implementation of the machine
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does not execute HLT in
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.Dq Pa Idle CPU.
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On some implementations that do not support CPU clock slowdown, APM
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might not execute HLT.
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.Nm apm
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disables
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.Sy APMIO_NOTHALTCPU
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operation on such machines.
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.Pp
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The current version of
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.Nm apm
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does not call
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.Dq Pa Idle CPU
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from the kernel context switch routine if clock slowdown is not supported,
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and it executes HLT instruction by default. Therefore, there is
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no need to use these two operations in most cases.
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.El
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.Pp
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These interfaces are used by
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.Xr apm 8 .
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.It
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.Nm apm
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polls APM events and handles the following events.
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.Bl -column PMEV_POWERSTATECHANGEXXX "suspend system xxxxx"
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.It Sy "Name " "Action " "Description"
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.It Dv "PMEV_STANDBYREQ " No "suspend system " "standby request"
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.It Dv "PMEV_SUSPENDREQ " No "suspend system " "suspend request"
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.It Dv "PMEV_USERSUSPENDREQ " No "suspend system " "user suspend request"
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.It Dv "PMEV_CRITSUSPEND " No "suspend system " "critical suspend request"
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.It Dv "PMEV_NORMRESUME " No "resume system " "normal resume"
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.It Dv "PMEV_CRITRESUME " No "resume system " "critical resume"
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.It Dv "PMEV_STANDBYRESUME " No "resume system " "standby resume"
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.It Dv "PMEV_BATTERYLOW " No "notify message " "battery low"
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.It Dv "PMEV_UPDATETIME " No "adjust clock " "update time"
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.El
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.El
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.Sh BUGS
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WARNING! Many, if not most, of the implementations of APM-bios in laptops
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today are buggy. You may be putting your LCD-display and batteries at
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a risk by using this interface. (The reason this isn't a problem for
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MS-windows is that they use the real-mode interface.) If you see any
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weird behavior from your system with this code in use, unplug the
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power and batteries ASAP, if not immediately, and disable this code.
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.Pp
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We are very interested in getting this code working, so please send you
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observations of any anomalous behavior to us.
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.Pp
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When
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.Nm apm
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is active, calling the BIOS setup routine by using hot-keys,
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may cause serious trouble when resuming the system.
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BIOS setup programs should be called during bootstrap, or from DOS.
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.Pp
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Some APM implementations cannot handle events such as pushing the
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power button or closing the cover. On such implementations, the system
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.Ar must
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be suspended
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.Ar only
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by using
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.Xr apm 8
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or
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.Xr zzz 8 .
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.Pp
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Disk spin-down, LCD backlight control, and power on demand have not
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been supported on the current version.
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.Sh SEE ALSO
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.Xr apm 8 ,
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.Xr zzz 8
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.Sh AUTHORS
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Tatsumi Hosokawa <hosokawa@jp.FreeBSD.org>
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