














   X Display Power Management Signaling (DPMS) Extension

		   Protocol Specification



		    Version 0.5 (DRAFT)






			Rob Lembree
		    lembree@zk3.dec.com
	       Digital Equipment Corporation
		       24 April 1996








































Copyright (C) Digital Equipment Corporation, 1996

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 pur-
pose of the information in this document.  This documenta-
tion is provided ``as is'' without express or implied war-
ranty.
























































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 associ-
ated 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 con-
trol requires an extension to the core X Window System Pro-
tocol, 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 implementa-
tion works independently from the screen saver so that pol-
icy as it pertains to the interaction between screen saver
and DPMS can be deferred to the user or screen saver appli-
cation. 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 suf-
ficient 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 dis-
able 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 Electron-
ics Standards Association (VESA) Display Power Management
Signaling (DPMS) standard.  These are:


DPMS Extension Power Levels
  0	       DPMSModeOn	   In use
-----------
1. X Window System is a trademark of X Consortium,
Inc.



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Display Power Management Signaling (DPMS) Extension    DRAFT


  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 com-
pletely.


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_ver-
sion indicate what version of the protocol the client wants
the server to implement.  The server version numbers
returned indicate the protocol this extension actually sup-
ports.	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 revi-
sions 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).





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Display Power Management Signaling (DPMS) Extension    DRAFT


DPMSCapable

	=>

     capable: BOOL

This request is used to determine whether or not the cur-
rently running server's devices are capable of DPMS opera-
tions.	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 sus-
pend mode.  A value of zero indicates that this mode is dis-
abled.

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 consid-
ered 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 implemen-
tation defined, but in DPMS compliant hardware, is imple-
mented by shutting off both horizontal and vertical sync
signals, resulting in the power-down of the monitor.  Recov-
ery time is implementation dependant, but frequently is sim-
ilar to the power-up time of the monitor. A value of zero



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Display Power Management Signaling (DPMS) Extension    DRAFT


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 inactiv-
ity 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.  Sus-
pend mode is most often implemented by pulsing the horizon-
tal 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 verti-
cal 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

	=>





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Display Power Management Signaling (DPMS) Extension    DRAFT


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 with-
out 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, DPMSMode-
Standby, 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 DPMS-
Disabled.  If state is DPMSEnabled, power_level is returned
as one of DPMSModeOn, DPMSModeStandby, DPMSModeSuspend or
DPMSModeOff, otherwise it is undefined.


3.  Events and Errors

No new events or errors are defined by this extension.

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





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Display Power Management Signaling (DPMS) Extension    DRAFT


 =>
  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





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Display Power Management Signaling (DPMS) Extension    DRAFT


 =>



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



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Display Power Management Signaling (DPMS) Extension    DRAFT


     2	       DPMSModeSuspend
     3	       DPMSModeOff
  1  BOOL		 state
  21			 unused





















































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