APM(4)

NAME
apm - Advanced Power Management pseudo-device driver

SYNOPSIS
apm0 at mainbus0
#include <machine/apmvar.h>
/dev/apm

DESCRIPTION
The apm driver provides support for the Advanced Power Managment features of some i386 system BIOSes. The driver supports the Advanced Power Management (APM) BIOS Interface Specification (revision 1.1), published jointly by the Intel Corporation and the Microsoft Corporation.

The boot loader connects to the APM bios while the system is still operating in i386 real mode, and places the APM bios into 32-bit protected mode operation. The NetBSD kernel start-up routines establish the 32-bit protected mode connection to the APM BIOS.

The APM driver's behavior may be adjusted by specifying any of the following kernel configuration options:
APM_NO_IDLE
    Do not call the BIOS CPU idle function from the system idle loop. (Some systems will hang on certain device accesses, such as sound cards or floppy diskette drives, without this option)
APM_V10_ONLY
    Use only the APM revision 1.0 specification calls. (Some systems do not implement APM v1.1 very well, and generate weird events instead of the expected events when the system suspend key is pressed.)
APM_NO_POWEROFF
    Do not attempt to turn off power when halting the system.
APM_FORCE_64KSEG
    Force the length of the APM BIOS code and data segments to 64KB.
APMDEBUG
    Enable kernel printout of events received from the APM BIOS.
APMCALLDEBUG
    Enable kernel printout of every call to the APM BIOS (this is very noisy).
APM_DISABLE_INTERRUPTS
    Set this to zero if you don't want the kernel to disable interrupts before calling the BIOS. This is required for most IBM ThinkPads, and some other newer laptops. A good indication that you need this is that the machine hangs just after resuming from suspended state. It's unclear if doing this has negative effects on older BIOS, therefore it defaults to one (i.e interrupts are disabled).

If no processes are holding open file descriptors to the APM device, the driver will process the APM BIOS events itself. If a process has the device open for write, the driver defers all suspend and standby processing to the user process as long as there is sufficient queue space to store the event for the process. If the device is only open for read, the driver will report events but handle them itself.

The APM device may be opened by multiple readers but only one writer. Multiple readers may fetch the status with ioctl(2) without worrying about interference, but they must cooperate to share events as only a single event queue is provided. The device may only be select(2) ed or manipulated with ioctl(2); read(2) and write(2) are not supported. The ioctl(2) calls supported are:
APM_IOC_SUSPEND
    Initiate an APM suspend mode. This is a deep sleep mode which powers down most devices. The device must be open for writing for this command to succeed.
APM_IOC_STANDBY
    Initiate an APM standby mode. This is a light sleep mode from which the system can quickly restore normal operation. The device must be open for writing for this command to succeed.
APM_IOC_GETPOWER
    Fetch the current power status into an apm_power_info structure.

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

    battery_state is one of APM_BATT_HIGH, APM_BATT_LOW, APM_BATT_CRITICAL, APM_BATT_CHARGING, or APM_BATT_UNKNOWN. ac_state is one of APM_AC_OFF, APM_AC_ON, APM_AC_BACKUP, or APM_AC_UNKNOWN. battery_life is the percentage estimated remaining normal battery life (or 0 if the BIOS cannot provide an estimate). minutes_left is an estimated remaining lifetime (or 0 if the BIOS cannot provide an estimate).
APM_IOC_NEXTEVENT
    Fetch the next event from the APM BIOS into an apm_event_info structure. If no more events are ready, this will return EAGAIN.

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

    type is one of the APM event types (APM_STANDBY_REQ through APM_SYS_STANDBY_RESUME). index is the ordinal event sequence number.

SEE ALSO
apmd(8)

REFERENCES
Advanced Power Management (APM) BIOS Interface Specification (Revision 1.1), Intel Corporation and Microsoft Corporation. Intel order number 241704-001; Microsoft part number 781-110-X01.

HISTORY
The apm pseudo-device driver appeared in NetBSD 1.3.