APM(4)

NAME
apm - advanced power management device interface

SYNOPSIS
apm0 at bios0 flags 0x0000

DESCRIPTION
The apm driver provides an interface to the Advanced Power Management (APM) BIOS functions. The driver supports versions 1.0, 1.1, and 1.2 interface specifications.

This driver also provides an interface to acpi(4) on some machines.

The low two bytes of the flags specify the version of the specification driver should conform to in binary decimal notation. The value of 0x0101 would specify version 1.1 of the interface specification to be used.

The value of 0x10000 specifies whether to leave interrupts enabled when calling APM BIOS routines. This is needed for some IBM laptops, the symptoms are hangs and freezes on suspend, stand by, and hibernation activities.

The value of 0x20000 specifies to swap the bytes of the battery life estimation (the DX register) as given from the APM BIOS. This is needed for some SONY VAIO laptops, such as some 505 models.

Configuration options:

APMDEBUG
    Enable various driver status messages.
DIAGNOSTIC
    Enable debugging messages.
DEBUG
    Enable other debugging messages.

The apm driver implements the following ioctl(2) calls. They are defined in <machine/apmvar.h>.

APM_IOC_REJECT
    Not implemented. DO NOT USE.

APM_IOC_STANDBY
    (no parameters) Request “standby” mode.

APM_IOC_SUSPEND
    (no parameters) Request “suspend” mode.

APM_IOC_GETPOWER
    (struct apm_power_info) Request the current power state. The argument structure is as follows:

        struct apm_power_info {
        	u_char battery_state;
        	u_char ac_state;
        	u_char battery_life;
        	u_char spare1;
        	u_int minutes_left;
        	u_int spare2[6];
        };

    The following values are defined for battery_state:

    APM_BATT_HIGH
        Battery has a high state of charge.

    APM_BATT_LOW
        Battery has a low state of charge.

    APM_BATT_CRITICAL
        Battery has a critical state of charge.

    APM_BATT_CHARGING
        Battery is not high, low, or critical and is currently charging.

    APM_BATT_UNKNOWN
        Cannot read the current battery state.

    APM_BATTERY_ABSENT
        No battery installed.

    The following values are defined for ac_state:

    APM_AC_OFF
        External power not detected.

    APM_AC_ON
        External power detected.

    APM_AC_BACKUP
        Backup power in use.

    APM_AC_UNKNOWN
        External power state unknown.

    The battery_life value contains the estimated percentage of battery life available. 100% indicates a full charge.

    The minutes_left value contains the estimated number of minutes of battery life remaining.

APM_IOC_NEXTEVENT
    (struct apm_event_info) The APM driver stores up to APM_NEVENTS events. This was defined as 16 at the time this documentation was written. If the event list is full when a new event is detected the new event is lost. APM_IOC_NEXTEVENT ioctl returns the next event on the list or EAGAIN if the event list is empty. The format of the returned event is:

        struct apm_event_info {
        	u_int type;
        	u_int index;
        	u_int spare[8];
        };

    where index is a sequential count of events that can be used to check if any events were lost and type is one of:
    APM_STANDBY_REQ
    APM_SUSPEND_REQ
    APM_NORMAL_RESUME
    APM_CRIT_RESUME
    APM_BATTERY_LOW
    APM_POWER_CHANGE
    APM_UPDATE_TIME
    APM_CRIT_SUSPEND_REQ
    APM_USER_STANDBY_REQ
    APM_USER_SUSPEND_REQ
    APM_SYS_STANDBY_RESUME

APM_IOC_DEV_CTL
    (struct apm_ctl) Allows an application to directly set the APM operating mode. The argument structure is as follows:

        struct apm_ctl {
        	u_int dev;
        	u_int mode;
        };

    dev indicates the device, typically APM_DEV_ALLDEVS.

    mode indicates the desired operating mode. Possible values are
    APM_SYS_READY
    APM_SYS_STANDBY
    APM_SYS_SUSPEND
    APM_SYS_OFF
    APM_LASTREQ_INPROG
    APM_LASTREQ_REJECTED

APM_IOC_PRN_CTL
    (int) This ioctl(2) controls message output by the APM driver when a power change event is detected. The integer parameter is one of:

    APM_PRINT_ON
        All power change events result in a message. This is the normal operating mode for the driver.

    APM_PRINT_OFF
        Power change event messages are suppressed.

    APM_PRINT_PCT
        Power change event messages are suppressed unless the estimated battery life percentage changes.

    However, in no case will power status messages be displayed until the battery life goes below the percentage in the sysctl(8) state variable machdep.apmwarn. Setting machdep.apmwarn to zero disables all warnings regardless of the APM_IOC_PRN_CTL setting.

As noted above, the operation of the APM driver can be modified using the machdep.apmwarn sysctl(8) variable. Another driver modifier is the machdep.apmhalt variable. When machdep.apmhalt is set to 1 the APM power down code is modified in a way necessary for correct operation on some systems, mainly IBM laptops. If your system does not power down when given the command halt -p try setting machdep.apmhalt to 1 using sysctl(8). The variable can be set at boot time in sysctl.conf(5).

FILES

/dev/apm
    Power management data device. May only be opened read-only. May be opened by multiple concurrent users.

/dev/apmctl
    Power management control device. May be opened read-write or write-only. May only be opened by one user at a time. An attempt to open the file when in use will fail, returning EBUSY.

SEE ALSO
acpi(4), intro(4), sysctl.conf(5), apm(8), apmd(8), halt(8), sysctl(8)

HISTORY
The apm driver source code contains these copyrights:

Copyright (c) 1995 John T. Kohl. All rights reserved.
Copyright (C) 1994 by HOSOKAWA Tatsumi <hosokawa@mt.cs.keio.ac.jp>

...and has been hacked on by many others since.

BUGS
Not all the BIOSes support power down the way we are attempting to execute it.

Not all BIOS vendors even read the specification.