path: root/specs/dpms.xml

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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
                   "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">

<book id="dpms">

<bookinfo>
   <title>X Display Power Management Signaling (DPMS) Extension Protocol Specification</title>
   <subtitle>X Project Team Standard</subtitle>
   <releaseinfo>Version 1.0</releaseinfo>
   <authorgroup>
      <author>
         <firstname>Rob </firstname><surname>Lembree</surname>
         <affiliation><orgname>Digital Equipment Corporation</orgname></affiliation>
         <email>lembree@zk3.dec.com</email>
      </author>
   </authorgroup>
   <corpname>X Consortium Standard</corpname>
   <copyright><year>1996</year><holder>Digital Equipment Corporation</holder></copyright>
   <affiliation><orgname>X Consortium</orgname></affiliation>
   <productnumber>X Version 11, Release 6.8</productnumber>

<legalnotice>
<para>
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.
</para>

</legalnotice>
</bookinfo>

<chapter id="Overview">
<title>Overview</title>
<para>
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.<footnote>
<para>
<emphasis remap='I'>X Window System</emphasis> is a trademark of The Open Group.
</para>
</footnote>
</para>


<para>
<!-- .LP -->
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.
</para>
<para>
<!-- .LP -->
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.
</para>
<para>
<!-- .LP -->
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.
</para>
<para>
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.
</para>
<para>
There are four power levels specified by the Video Electronics Standards
Association (VESA) Display Power Management Signaling (DPMS) standard.
These are:
</para>

<literallayout class="monospaced">
<function>DPMS Extension Power Levels</function>
     0     DPMSModeOn          In use
     1     DPMSModeStandby     Blanked, low power
     2     DPMSModeSuspend     Blanked, lower power
     3     DPMSModeOff         Shut off, awaiting activity
</literallayout>

<para>
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.
</para>

<para>
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.
</para>
</chapter>

<chapter id="Requests">
<title>Requests</title>
<para>
<function>DPMSGetVersion</function>
</para>

<informaltable frame="none">
  <tgroup cols='1' align='left'>
  <colspec colname='c1' colsep="0" colwidth="1*"/>
  <tbody>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>client_major_version</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>client_minor_version</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>=&gt;</entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>server_major_version</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>server_minor_version</emphasis>: CARD16
      </entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
If supplied, the <emphasis remap='I'>client_major_version</emphasis> and
<emphasis remap='I'>client_minor_version</emphasis> 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
<emphasis remap='I'>server_major_version</emphasis> and the
<emphasis remap='I'>server_minor_version</emphasis> 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
<emphasis remap='I'>server_major_version</emphasis>
of one (1), and a <emphasis remap='I'>server_minor_version</emphasis>
of one (1).
</para>

<para>
<function>DPMSCapable</function>
</para>

<informaltable frame="none">
  <tgroup cols='1' align='left'>
  <colspec colname='c1' colsep="0" colwidth="1*"/>
  <tbody>
    <row rowsep="0">
      <entry>=&gt;</entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>capable</emphasis>: BOOL
      </entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
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.
</para>

<para>
<function>DPMSGetTimeouts</function>
</para>

<informaltable frame="none">
  <tgroup cols='1' align='left'>
  <colspec colname='c1' colsep="0" colwidth="1*"/>
  <tbody>
    <row rowsep="0">
      <entry>=&gt;</entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>standby_timeout</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>suspend_timeout</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>off_timeout</emphasis>: CARD16
      </entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
This request returns the current values of the DPMS timeout values.  All
values are in units of seconds.
</para>

<para>
<emphasis remap='I'>standby_timeout</emphasis> 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.
</para>

<para>
<emphasis remap='I'>suspend_timeout</emphasis> 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.
</para>

<para>
<emphasis remap='I'>off_timeout</emphasis> 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.
</para>

<para>
<function>DPMSSetTimeouts</function>
</para>

<informaltable frame="none">
  <tgroup cols='1' align='left'>
  <colspec colname='c1' colsep="0" colwidth="1*"/>
  <tbody>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>standby_timeout</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>suspend_timeout</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>off_timeout</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>=&gt;</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>


<para>
All values are in units of seconds.
<emphasis remap='I'>standby_timeout</emphasis> 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.
</para>

<para>
The <emphasis remap='I'>suspend_timeout</emphasis> 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.
</para>

<para>
The <emphasis remap='I'>off_timeout</emphasis> 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.
</para>
<para>
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.
</para>
<para>
<function>DPMSEnable</function>
</para>
<para>
=&gt;
</para>

<para>
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.
</para>

<para>
<function>DPMSDisable</function>
</para>
<para>
=&gt;
</para>

<para>
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.
</para>

<para>
<function>DPMSForceLevel</function>
</para>

<informaltable frame="none">
  <tgroup cols='1' align='left'>
  <colspec colname='c1' colsep="0" colwidth="1*"/>
  <tbody>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>power_level</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>=&gt;</entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
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.
</para>

<para>
<function>DPMSInfo</function>
</para>

<informaltable frame="none">
  <tgroup cols='1' align='left'>
  <colspec colname='c1' colsep="0" colwidth="1*"/>
  <tbody>
    <row rowsep="0">
      <entry>=&gt;</entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>power_level</emphasis>: CARD16
      </entry>
    </row>
    <row rowsep="0">
      <entry>
<emphasis remap='I'>state</emphasis>: BOOL
      </entry>
    </row>
  </tbody>
  </tgroup>
</informaltable>

<para>
This request returns information about the current DPMS state of the
display.  <emphasis remap='I'>state</emphasis> is one of DPMSEnabled
or DPMSDisabled.
If <emphasis remap='I'>state</emphasis> is DPMSEnabled,
<emphasis remap='I'>power_level</emphasis> is returned as one
of DPMSModeOn, DPMSModeStandby, DPMSModeSuspend or DPMSModeOff, otherwise
it is undefined.
</para>

</chapter>

<chapter id="Events_and_Errors">
<title>Events and Errors</title>
<para>
No new events or errors are defined by this extension.
</para>
</chapter>

<chapter id="Encoding">
<title>Encoding</title>
<para>
Please refer to the X11 Protocol Encoding document as this document uses
conventions established there.
</para>

<para>
The name of this extension is "DPMS".
</para>

<literallayout class="monospaced">
<function>DPMSGetVersion</function>
     1     CARD8         opcode
     1     0             DPMS opcode
     2     2             request length
     2     CARD16        client_major_version
     2     CARD16        client_minor_version
=&gt;
     1     1             Reply
     1                   unused
     2     CARD16        sequence number
     4     0             length
     2     CARD16        server_major_version
     2     CARD16        server_minor_version
     20                  unused
</literallayout>

<literallayout class="monospaced">
<function>DPMSCapable</function>
     1     CARD8         opcode
     1     1             DPMS opcode
     2     1             request length
=&gt;
     1     1             Reply
     1                   unused
     2     CARD16        sequence number
     4     0             length
     1     BOOL          capable
     23                  unused
</literallayout>

<literallayout class="monospaced">
<function>DPMSGetTimeouts</function>
     1     CARD8         opcode
     1     2             DPMS opcode
     2     1             request length
=&gt;
     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
</literallayout>

<literallayout class="monospaced">
<function>DPMSSetTimeouts</function>
     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
=&gt;
</literallayout>

<literallayout class="monospaced">
<function>DPMSEnable</function>
     1     CARD8         opcode
     1     4             DPMS opcode
     2     1             request length
 =&gt;
</literallayout>

<literallayout class="monospaced">
<function>DPMSDisable</function>
     1     CARD8         opcode
     1     5             DPMS opcode
     2     1             request length
 =&gt;
</literallayout>

<literallayout class="monospaced">
<function>DPMSForceLevel</function>
     1     CARD8         opcode
     1     6             DPMS opcode
     2     2             request length
     2                   power_level
          0     DPMSModeOn
          1     DPMSModeStandby
          2     DPMSModeSuspend
          3     DPMSModeOff
     2                   unused
=&gt;
</literallayout>

<literallayout class="monospaced">
<function>DPMSInfo</function>
     1     CARD8         opcode
     1     7             DPMS opcode
     2     1             request length
=&gt;
     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

</literallayout>
</chapter>
</book>