X Display Power Management Signaling (DPMS) Extension Protocol Specification

X Project Team 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
notice and this permission notice appear in all copies. Digital Equipment
Corporation makes no representations about the suitability for any purpose of
the information in this document. This documentation is provided “as is”
without express or implied warranty.

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Table of Contents

1. Overview
2. Requests
3. Events and Errors
4. Encoding

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.^[1]

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.

The design goal of the DPMS extension is to be a logical extension to the
traditional screen saver. The protocol and sample implementation is designed to
use the same date types and time units as the screen saver. The sample
implementation works independently from the screen saver so that policy as it
pertains to the interaction between screen saver and DPMS can be deferred to
the user or screen saver application. The extension has been tested with and
shown to work correctly with both the internal blanking and non-blanking screen
savers, as well as with screen saver extension clients.

The DPMS extension is designed to be simple, yet export sufficient VESA DPMS
information to enable full function clients to be written. Included is the
ability to sense DPMS capability, set and get DPMS timeouts, enable and disable
individual DPMS modes, enable and disable DPMS (without destroying timeout
values), and sense current DPMS on/off state and power level.

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

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

It is logical to assume that successive DPMS modes be chronologically at the
same time or later than one another, and the protocol is designed to enforce
this rule.

Note however that a concious decision is made to decouple the timeouts
associated with screen saver from the DPMS timeouts. While it might be
considered logical to require that the first non-zero DPMS timeout be greater
than or equal to the screen saver timeout, this is intentionally omitted,
leaving this policy decision to the user or the screen saver application. In
the case of a laptop where power may be scarce, the importance of power savings
should supersede the screen saver. If the laptop user plugs the unit in and
power is no longer a scarce commodity, it may be decided to make DPMS less
aggressive, or disable it completely.


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^[1] X Window System is a trademark of The Open Group.

Chapter 2. Requests

DPMSGetVersion

client_major_version: CARD16
client_minor_version: CARD16
=>
server_major_version: CARD16
server_minor_version: CARD16

If supplied, the client_major_version and client_minor_version indicate what
version of the protocol the client wants the server to implement. The server
version numbers returned indicate the protocol this extension actually
supports. This might not equal the version sent by the client. An
implementation can (but need not) support more than one version simultaneously.
The server_major_version and the server_minor_version are a mechanism to
support future revisions of the Display Power Management Signaling protocol
which may be necessary. In general, the major version would increment for
incompatible changes, and the minor version would increment for small,
upward-compatible changes. Servers that support the protocol defined in this
document will return a server_major_version of one (1), and a 
server_minor_version of one (1).

DPMSCapable

=>
capable: BOOL

This request is used to determine whether or not the currently running server's
devices are capable of DPMS operations. The truth value of this request is
implementation defined, but is generally based on the capabilities of the
graphic card and monitor combination. Also, the return value in the case of
heterogeneous multi-head servers is implementation defined.

DPMSGetTimeouts

=>
standby_timeout: CARD16
suspend_timeout: CARD16
off_timeout: CARD16

This request returns the current values of the DPMS timeout values. All values
are in units of seconds.

standby_timeout is the amount of time of inactivity 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 indicates that
this mode is disabled.

suspend_timeout is the amount of time of inactivity 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 indicates that this mode is disabled.

off_timeout is the amount of time of inactivity 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 indicates that this mode is disabled.

DPMSSetTimeouts

standby_timeout: CARD16
suspend_timeout: CARD16
off_timeout: CARD16
=>

All values are in units of seconds. standby_timeout is the amount of time of
inactivity before standby mode will be invoked. This is the lightest level of
power savings, and the monitor is generally immediately ready upon detection of
user activity. This is most often implemented by shutting off the horizontal
sync signal to the monitor. A value of zero disables this mode.

The suspend_timeout specifies the amount of time of inactivity before the
screen is placed into suspend mode. Suspend mode is the middle level of power
savings, resulting in a slightly longer recovery upon detection of activity.
Suspend mode is most often implemented by pulsing the horizontal sync signal,
and removing the vertical sync signal. A value of zero disables this mode.

The off_timeout specifies the amount of time of inactivity before the monitor
is shut off. Off mode is the deepest level of power management, resulting in
the greatest power savings and the longest recovery time. Off mode is most
often implemented by removing both the horizontal and vertical signals. A value
of zero disables this mode.

The values of successive power levels must be greater than or equal to the
value of the previous (non-zero) level. A BadValue error is generated if an
illegal combination is detected.

DPMSEnable

=>

This request enables the DPMS characteristics of the server, using the server's
currently stored timeouts. If DPMS is already enabled, no change is effected.

DPMSDisable

=>

This request disables the DPMS characteristics of the server. It does not
affect the core or extension screen savers. If DPMS is already disabled, no
change is effected. This request is provided so that DPMS may be disabled
without damaging the server's stored timeout values.

DPMSForceLevel

power_level: CARD16
=>

This request forces a specific DPMS level on the server. If DPMS is disabled, a
BadMatch error is generated. If an erroneous power level is specified, a
BadValue error is returned, and the error value contains the bad value. If the
power level specified is already in effect, no changes occur. Power Level must
be one of DPMSModeOn, DPMSModeStandby, DPMSModeSuspend or DPMSModeOff.

DPMSInfo

=>
power_level: CARD16
state: BOOL

This request returns information about the current DPMS state of the display. 
state is one of DPMSEnabled or DPMSDisabled. If state is DPMSEnabled, 
power_level is returned as one of DPMSModeOn, DPMSModeStandby, DPMSModeSuspend
or DPMSModeOff, otherwise it is undefined.

Chapter 3. Events and Errors

No new events or errors are defined by this extension.

Chapter 4. Encoding

Please refer to the X11 Protocol Encoding document as this document uses
conventions established there.

The name of this extension is "DPMS".

DPMSGetVersion
     1     CARD8         opcode
     1     0             DPMS opcode
     2     2             request length
     2     CARD16        client_major_version
     2     CARD16        client_minor_version
=>
     1     1             Reply
     1                   unused
     2     CARD16        sequence number
     4     0             length
     2     CARD16        server_major_version
     2     CARD16        server_minor_version
     20                  unused

DPMSCapable
     1     CARD8         opcode
     1     1             DPMS opcode
     2     1             request length
=>
     1     1             Reply
     1                   unused
     2     CARD16        sequence number
     4     0             length
     1     BOOL          capable
     23                  unused

DPMSGetTimeouts
     1     CARD8         opcode
     1     2             DPMS opcode
     2     1             request length
=>
     1     1             Reply
     1                   unused
     2     CARD16        sequence number
     4     0             length
     2     CARD16        standby_timeout
     2     CARD16        suspend_timeout
     2     CARD16        off_timeout
     18                  unused

DPMSSetTimeouts
     1     CARD8         opcode
     1     3             DPMS opcode
     2     3             request length
     2     CARD16        standby_timeout
     2     CARD16        suspend_timeout
     2     CARD16        off_timeout
     2                   unused
=>

DPMSEnable
     1     CARD8         opcode
     1     4             DPMS opcode
     2     1             request length
 =>

DPMSDisable
     1     CARD8         opcode
     1     5             DPMS opcode
     2     1             request length
 =>

DPMSForceLevel
     1     CARD8         opcode
     1     6             DPMS opcode
     2     2             request length
     2                   power_level
          0     DPMSModeOn
          1     DPMSModeStandby
          2     DPMSModeSuspend
          3     DPMSModeOff
     2                   unused
=>

DPMSInfo
     1     CARD8         opcode
     1     7             DPMS opcode
     2     1             request length
=>
     1     1             Reply
     1                   unused
     2     CARD16        sequence number
     4     0             length
     2                   power_level
           0     DPMSModeOn
           1     DPMSModeStandby
           2     DPMSModeSuspend
           3     DPMSModeOff
     1     BOOL          state
     21                  unused


