NAME¶
apm —
APM BIOS interface
SYNOPSIS¶
device apm
DESCRIPTION¶
apm is an interface to the Intel / Microsoft APM (Advanced
Power Management) BIOS on laptop PCs.
apm provides the following power management functions.
- When the system wakes up from suspended mode,
apm adjusts the system clock to RTC.
- When the system wakes up from suspended mode,
apm passes a message to syslogd(8)
comprising of system wakeup time and elapsed time during suspended
mode.
- 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.
- apm exports an application interface as
a character device. Applications can control APM, or retrieve APM status
information via this interface. apm exports the
following interfaces. These symbols are defined in
<machine/apm_bios.h>.
- APMIO_SUSPEND
- Suspend system.
- APMIO_GET
- Get power management information.
- APMIO_ENABLE
-
- APMIO_DISABLE
- Enable / Disable power management.
- APMIO_HALTCPU
-
- APMIO_NOTHALTCPU
- Control execution of HLT in the kernel context switch
routine.
- APMIO_GETPWSTATUS
- Get per battery information.
Some APM implementations execute the HLT (Halt CPU until an interrupt
occurs) instruction in the “Idle CPU”
call, while others do not. Thus enabling this may result in redundant
HLT executions because “Idle CPU” is
called from the kernel context switch routine that inherently executes
HLT. This may reduce peak system performance.
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 “Idle CPU”. On
some implementations that do not support CPU clock slowdown, APM might
not execute HLT. apm disables
APMIO_NOTHALTCPU operation on such machines.
The current version of apm does not call
“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.
These interfaces are used by apm(8).
- apm polls APM events and handles the
following events.
Name Action Description |
PMEV_STANDBYREQ
suspend system standby request |
PMEV_SUSPENDREQ
suspend system suspend request |
PMEV_USERSUSPENDREQ
suspend system user suspend request |
PMEV_CRITSUSPEND
suspend system critical suspend request |
PMEV_NORMRESUME
resume system normal resume |
PMEV_CRITRESUME
resume system critical resume |
PMEV_STANDBYRESUME
resume system standby resume |
PMEV_BATTERYLOW
notify message battery low |
PMEV_UPDATETIME
adjust clock update time |
SEE ALSO¶
apm(8),
zzz(8)
AUTHORS¶
Tatsumi Hosokawa <hosokawa@jp.FreeBSD.org>
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 is not a problem for MS-Windows is that
they use the real-mode interface.) If you see any weird behavior from your
system with this code in use, unplug the power and batteries ASAP, if not
immediately, and disable this code.
We are very interested in getting this code working, so please send your
observations of any anomalous behavior to us.
When
apm is active, calling the BIOS setup routine by using
hot-keys, may cause serious trouble when resuming the system. BIOS setup
programs should be called during bootstrap, or from DOS.
Some APM implementations cannot handle events such as pushing the power button
or closing the cover. On such implementations, the system
must be suspended
only by using
apm(8) or
zzz(8).
Disk spin-down, LCD backlight control, and power on demand have not been
supported on the current version.