X Display Power Management Signaling (DPMS) Extension

X Consortium Standard

Rob Lembree

Digital Equipment Corporation
<lembree@zk3.dec.com>

X Version 11, Release 7.7

Version 1.0

Copyright © 1996 Digital Equipment Corporation

Permission to use, copy, modify, distribute, and sell this documentation for
any purpose is hereby granted without fee, provided that the above copyright
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Table of Contents

1. Overview
2. DPMS Functions

Chapter 1. Overview

This extension provides X Protocol control over the VESA Display Power
Management Signaling (DPMS) characteristics of video boards under control of
the X Window System.

Traditionally, the X Window System has provided for both blanking and
non-blanking screen savers. Timeouts associated with these built-in screen
saver mechanisms are limited to idle (dwell) time, and a change timeout that
specifies the change interval for non-blanking screen savers.

The United States' Environmental Protection Agency (EPA) Energy Star program
requires that monitors power down after some idle time by default. While it is
possible to simply overload the existing screen saver timeouts, this solution
leaves the non-privileged user little to no control over the DPMS
characteristics of his or her system. For example, disabling DPMS would require
some unintended side effect in the core screen saver, such as disabling the
changing of a non-blanking screen saver. Providing clients with this control
requires an extension to the core X Window System Protocol, and this extension
seeks to fill this gap.

There are four power levels specified by the Video Electronics Standards
Association (VESA) Display Power Management Signaling (DPMS) standard. These
are mapped onto the X DPMS Extension like this:


DPMS Extension Power Levels
     0     DPMSModeOn               In use
     1     DPMSModeStandby          Blanked, low power
     2     DPMSModeSuspend          Blanked, lower power
     3     DPMSModeOff               Shut off, awaiting activity

Chapter 2. DPMS Functions

Bool DPMSQueryExtention(Display *display, int event_base, int error_base);

*display   Specifies the connection to the X server.

event_base Specifies the return location for the assigned base event

error_base Specifies the return location for the assigned base error

The DPMSQueryExtension function queries the X server to determine the
availability of the DPMS Extension. If the extension is available, the return
value is TRUE, and event_base and error_base are set to the base event number
and base error number for the extension, respectively. Otherwise, the return
value is FALSE, and the values of event_base and error_base are undefined.

Status DPMSGetVersion(Display *display, int *major_version, int
*minor_version);

display       Specifies the connection to the X server.

major_version Specifies the return location for the extension major version.

minor_version Specifies the return location for the extension minor version.

The DPMSGetVersion function returns the version of the DPMS extension
implemented by the X server. The version is returned in major_version and 
minor_version. The major version and minor version for this specification are
'1' and '1', respectively. The major version will be incremented for protocol
incompatible changes, and the minor version will be incremented for small,
upwardly compatible changes.

Bool DPMSCapable(Display *display);

display Specifies the connection to the X server.

The DPMSCapable function returns the DPMS capability of the X server, either
TRUE (capable of DPMS) or FALSE (incapable of DPMS). The capability of an X
server is implementation defined. For example, if a multi-headed X server is
capable of DPMS on one head, and incapable on another, the truth value of this
function is defined by the X server implementation.

Status DPMSSetTimeouts(Display *display, CARD16 standby, CARD16 suspend, CARD16
off);

display Specifies the connection to the X server.

standby Specifies the new standby timeout in seconds.

suspend Specifies the new suspend timeout in seconds.

off     Specifies the new off timeout in seconds.

The DPMSSetTimeouts function permits applications to set the timeout values
used by the X server for DPMS timings.

The value standby is the amount of time of inactivity in seconds before standby
mode is invoked. The actual effects of this mode are implementation defined,
but in the case of DPMS compliant hardware, it is implemented by shutting off
the horizontal sync signal, and pulsing the vertical sync signal. Standby mode
provides the quickest monitor recovery time. Note also that many monitors
implement this mode identically to suspend mode. A value of zero disables this
mode.

The value suspend is the amount of time of inactivity in seconds before the
second level of power savings is invoked. Suspend mode's physical and
electrical characteristics are implementation defined, but in DPMS compliant
hardware, results in the pulsing of the horizontal sync signal, and shutting
off of the vertical sync signal. Suspend mode recovery is considered to be
slower than standby mode, but faster than off mode, however this is monitor
dependent. As noted above, many monitors implement this mode identically to
standby mode. A value of zero disables this mode.

The value off is the amount of time of inactivity in seconds before the third
and final level of power savings is invoked. Off mode's physical and electrical
characteristics are implementation defined, but in DPMS compliant hardware, is
implemented by shutting off both horizontal and vertical sync signals,
resulting in the power-down of the monitor. Recovery time is implementation
dependant, but frequently is similar to the power-up time of the monitor. A
value of zero disables this mode.

Chronologically, standby mode occurs before or simultaneously with suspend
mode, and suspend mode must occur before or simultaneously with off mode.
Therefore, non-zero mode timeout values must be greater than or equal to the
timeout values of earlier modes. If inconsistent values are supplied, a
BadValue error will result.

Status DPMSGetTimeouts(Display *display, CARD16 *standby, CARD16 *suspend,
CARD16 *off);

display Specifies the connection to the X server.

standby Specifies the new standby timeout in seconds.

suspend Specifies the new suspend timeout in seconds.

off     Specifies the new off timeout in seconds.

The DPMSGetTimeouts function retrieves the timeout values used by the X server
for DPMS timings.

The value standby is the amount of time of inactivity in seconds before standby
mode is invoked. A value of zero indicates that this mode has been disabled.

The value suspend is the amount of time of inactivity in seconds before the
second level of power savings is invoked. A value of zero indicates that this
mode has been disabled.

The value off is the amount of time of inactivity in seconds before the third
and final level of power savings is invoked. A value of zero indicates that
this mode has been disabled.

Status DPMSEnable(Display *display);

display Specifies the connection to the X server.

The DPMSEnable function enables DPMS on the specified display. When enabled,
DPMS will use the currently saved timeout values, and will invoke the DPMS
power mode appropriate for the amount of time that the workstation input
devices have been idle. If DPMSEnable is invoked on a display with DPMS already
enabled, no change is made, and no error is returned. If DPMSEnable is invoked
on a display without support for DPMS, no change is made and no error is
returned.

Status DPMSDisable(Display *display);

display Specifies the connection to the X server.

The DPMSDisable function disables DPMS on the specified display. When disabled,
DPMS returns the display to DPMSModeOn. If DPMSDisable is invoked on a display
with DPMS already disabled, no change is made, and no error is returned. If
DPMSDisable is invoked on a display without support for DPMS, no change is made
and no error is returned.

Status DPMSForceLevel(Display *display, CARD16 level);

display Specifies the connection to the X server.

level   Specifies the level to force power to.

The DPMSForceLevel function forces a DPMS capable display into the specified
power level. The level must be one of DPMSModeOn, DPMSModeStandby,
DPMSModeSuspend, or DPMSModeOff. Values other than these will result in a
BadValue error. If DPMS is disabled on the display, a BadMatch protocol error
will result.

Status DPMSInfo(display, power_level, state)

Status DPMSInfo(Display *display, CARD16 power_level, BOOL *state);

display     Specifies the connection to the X server.

power_level Specifies the current power level.

state       Specifies the current DPMS state.

The DPMSInfo function returns information about the current DPMS state. The 
state return parameter indicates whether or not DPMS is enabled (TRUE) or
disabled (FALSE). The power_level return parameter indicates the current power
level (one of DPMSModeOn, DPMSModeStandby, DPMSModeSuspend, or DPMSModeOff.)

