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.
     __________________________________________________________

   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.
   __________________________________________________________

   ^[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
