is an interface to the Intel / Microsoft APM (Advanced Power Management) BIOS
on laptop PCs.
provides the following power management functions.
When the system wakes up from suspended mode,
adjusts the system clock to RTC.
When the system wakes up from suspended mode,
passes a message to
syslogd(8)
comprising of system wakeup time and elapsed time during suspended mode.
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.
exports an application interface as a character device.
Applications
can control APM, or retrieve APM status information via this interface.
exports the following interfaces.
These symbols are defined in
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.
disables
APMIO_NOTHALTCPU
operation on such machines.
The current version of
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.
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
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.
