X Synchronization Extension Protocol

X Consortium Standard

Tim Glauert

Olivetti Research
MultiWorks

Dave Carver

Digital Equipment Corporation
MIT/Project Athena

Jim Gettys

Digital Equipment Corporation
Cambridge Research Laboratory

David P. Wiggins

X Consortium, Inc.

James Jones

NVIDIA Corporation

X Version 11, Release 7.7

Version 3.1

Copyright © 1991 Olivetti Research Limited, Cambridge England, Digital
Equipment Corporation, Maynard, Massachusetts, X Consortium

Copyright © 2010 NVIDIA Corporation

Permission to use, copy, modify, and distribute this documentation for any
purpose and without fee is hereby granted, provided that the above copyright
notice appear in all copies. Olivetti, Digital, MIT, the X Consortium, and
NVIDIA make 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.

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X
CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of the X Consortium shall not be
used in advertising or otherwise to promote the sale, use or other dealings in
this Software without prior written authorization from the X Consortium.

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Table of Contents

1. Synchronization Protocol
    Description
    Types
    Errors
    Requests
    Events
2. Encoding
    Encoding New Types
    Encoding Errors
    Encoding Requests
    Encoding Events

Chapter 1. Synchronization Protocol

Table of Contents

Description
Types
Errors
Requests
Events

The core X protocol makes no guarantees about the relative order of execution
of requests for different clients. This means that any synchronization between
clients must be done at the client level in an operating system-dependent and
network-dependent manner. Even if there was an accepted standard for such
synchronization, the use of a network introduces unpredictable delays between
the synchronization of the clients and the delivery of the resulting requests
to the X server.

The core X protocol also makes no guarantees about the time at which requests
are executed, which means that all clients with real-time constraints must
implement their timing on the host computer. Any such timings are subject to
error introduced by delays within the operating system and network and are
inefficient because of the need for round-trip requests that keep the client
and server synchronized.

The synchronization extension provides primitives that allow synchronization
between clients to take place entirely within the X server. This removes any
error introduced by the network and makes it possible to synchronize clients on
different hosts running different operating systems. This is important for
multimedia applications, where audio, video, and graphics data streams are
being synchronized. The extension also provides internal timers within the X
server to which client requests can be synchronized. This allows simple
animation applications to be implemented without any round-trip requests and
makes best use of buffering within the client, network, and server.

Description

The mechanism used by this extension for synchronization within the X server is
to block the processing of requests from a client until a specific
synchronization condition occurs. When the condition occurs, the client is
released and processing of requests continues. Multiple clients may block on
the same condition to give inter-client synchronization. Alternatively, a
single client may block on a condition such as an animation frame marker.

The extension adds Counter, Alarm, and Fence to the set of resources managed by
the server. A counter has a 64-bit integer value that may be increased or
decreased by client requests or by the server internally. A client can block by
sending an Await request that waits until one of a set of synchronization
conditions, called TRIGGERs, becomes TRUE. Alarms generate events when counter
values go through a specified transition. A fence has two possible states:
triggered and not triggered. Client requests can put the fence in either of
these states. A client can block until one of a set of fences becomes triggered
by sending an AwaitFence request. Fences are bound to a particular screen at
creation time.

The CreateCounter request allows a client to create a Counter that can be
changed by explicit SetCounter and ChangeCounter requests. These can be used to
implement synchronization between different clients.

There are some counters, called System Counters, that are changed by the server
internally rather than by client requests. The effect of any change to a system
counter is not visible until the server has finished processing the current
request. In other words, system counters are apparently updated in the gaps
between the execution of requests rather than during the actual execution of a
request. The extension provides a system counter that advances with the server
time as defined by the core protocol, and it may also provide counters that
advance with the real-world time or that change each time the CRT screen is
refreshed. Other extensions may provide their own extension-specific system
counters.

The extension provides an Alarm mechanism that allows clients to receive an
event on a regular basis when a particular counter is changed.

The CreateFence request allows a client to create a Fence that can be triggered
and reset using TriggerFence and ResetFence requests, respectively. CreateFence
takes a drawable argument that implies which screen the fence should be created
on. The TriggerFence request changes the fence's state only after all previous
rendering commands affecting objects owned by the given fence's screen have
completed. Note that while fence objects are bound to a screen and the simple
trigger operation provided by this extension operates at screen granularity,
other extensions may add more fine-grained trigger operations based on any
number of events. The screen binding merely establishes an upper bound for the
scope of fence operations.

Types

Please refer to the X11 Protocol specification as this document uses syntactic
conventions established there and references types defined there.

The following new types are used by the extension.

INT64:                 64-bit signed integer
COUNTER:               XID
VALUETYPE:             {Absolute,Relative};
TESTTYPE:              {PositiveTransition,NegativeTransition,
                        PositiveComparison,NegativeComparison}
TRIGGER:               [
                        counter:COUNTER,
                        value-type:VALUETYPE,
                        wait-value:INT64,
                        test-type:TESTTYPE
                       ]
WAITCONDITION:         [
                        trigger:TRIGGER,
                        event-threshold:INT64
                       ]
SYSTEMCOUNTER:         [
                        name:STRING8,
                        counter:COUNTER,
                        resolution:INT64
                       ]
ALARM:                 XID
ALARMSTATE:            {Active,Inactive,Destroyed}
FENCE:                 XID

The COUNTER type defines the client-side handle on a server Counter. The value
of a counter is an INT64.

The TRIGGER type defines a test on a counter that is either TRUE or FALSE. The
value of the test is determined by the combination of a test value, the value
of the counter, and the specified test-type.

The test value for a trigger is calculated using the value-type and wait-value
fields when the trigger is initialized. If the value-type field is not one of
the named VALUETYPE constants, the request that initialized the trigger will
return a Value error. If the value-type field is Absolute, the test value is
given by the wait-value field. If the value-type field is Relative, the test
value is obtained by adding the wait-value field to the value of the counter.
If the resulting test value would lie outside the range for an INT64, the
request that initialized the trigger will return a Value error. If counter is
None and the value-type is Relative, the request that initialized the trigger
will return a Match error. If counter is not None and does not name a valid
counter, a Counter error is generated.

If the test-type is PositiveTransition, the trigger is initialized to FALSE,
and it will become TRUE when the counter changes from a value less than the
test value to a value greater than or equal to the test value. If the test-type
is NegativeTransition, the trigger is initialize to FALSE, and it will become
TRUE when the counter changes from a value greater than the test value to a
value less than or equal to the test value. If the test-type is
PositiveComparison, the trigger is TRUE if the counter is greater than or equal
to the test value and FALSE otherwise. If the test-type is NegativeComparison,
the trigger is TRUE if the counter is less than or equal to the test value and
FALSE otherwise. If the test-type is not one of the named TESTTYPE constants,
the request that initialized the trigger will return a Value error. A trigger
with a counter value of None and a valid test-type is always TRUE.

The WAITCONDITION type is simply a trigger with an associated event-threshold.
The event threshold is used by the Await request to decide whether or not to
generate an event to the client after the trigger has become TRUE. By setting
the event-threshold to an appropriate value, it is possible to detect the
situation where an Await request was processed after the TRIGGER became TRUE,
which usually indicates that the server is not processing requests as fast as
the client expects.

The SYSTEMCOUNTER type provides the client with information about a
SystemCounter. The name field is the textual name of the counter that
identifies the counter to the client. The counter field is the client-side
handle that should be used in requests that require a counter. The resolution
field gives the approximate step size of the system counter. This is a hint to
the client that the extension may not be able to resolve two wait conditions
with test values that differ by less than this step size. A microsecond clock,
for example, may advance in steps of 64 microseconds, so a counter based on
this clock would have a resolution of 64.

The only system counter that is guaranteed to be present is called SERVERTIME,
which counts milliseconds from some arbitrary starting point. The least
significant 32 bits of this counter track the value of Time used by the server
in Events and Requests. Other system counters may be provided by different
implementations of the extension. The X Consortium will maintain a registry of
system counter names to avoid collisions in the name space.

An ALARM is the client-side handle on an Alarm resource.

The FENCE type defines the client-side handle on a server Fence. A fence can
only be in one of two states, represented by a BOOL. If the value is TRUE, the
fence is in the triggered state. Otherwise, the fence is in the not triggered
state.

Errors

Counter This error is generated if the value for a COUNTER argument in a
        request does not name a defined COUNTER.

Alarm   This error is generated if the value for an ALARM argument in a request
        does not name a defined ALARM.

Fence   This error is generated if the value for a FENCE argument in a request
        does not name a defined FENCE.

Requests

                   version-major,version-minor: CARD8
                   =>
                   version-major,version-minor: CARD8

                   This request must be executed before any other requests for
                   this extension. If a client violates this rule, the results
                   of all SYNC requests that it issues are undefined. The
                   request takes the version number of the extension that the
                   client wishes to use and returns the actual version number
                   being implemented by the extension for this client. The
                   extension may return different version numbers to a client
Initialize         depending of the version number supplied by that client.
                   This request should be executed only once for each client
                   connection.

                   Given two different versions of the SYNC protocol, v1 and
                   v2, v1 is compatible with v2 if and only if v1.version_major
                   = v2.version_major and v1.version_minor <= v2.version_minor.
                   Compatible means that the functionality is fully supported
                   in an identical fashion in the two versions.

                   This document describes major version 3, minor version 1 of
                   the SYNC protocol.

                   =>
                   system-counters: LISTofSYSTEMCOUNTER
                   Errors: Alloc

ListSystemCounters This request returns a list of all the system counters that
                   are available at the time the request is executed, which
                   includes the system counters that are maintained by other
                   extensions. The list returned by this request may change as
                   counters are created and destroyed by other extensions.

                   id: COUNTER
                   initial-value: INT64
                   Errors: IDChoice,Alloc
CreateCounter
                   This request creates a counter and assigns the specified id
                   to it. The counter value is initialized to the specified
                   initial-value and there are no clients waiting on the
                   counter.

                   counter: COUNTER
                   Errors: Counter,Access

                   This request destroys the given counter and sets the counter
                   fields for all triggers that specify this counter to None.
                   All clients waiting on the counter are released and a
                   CounterNotify event with the destroyed field set to TRUE is
DestroyCounter     sent to each waiting client, regardless of the
                   event-threshold. All alarms specifying the counter become
                   Inactive and an AlarmNotify event with a state field of
                   Inactive is generated. A counter is destroyed automatically
                   when the connection to the creating client is closed down if
                   the close-down mode is Destroy. An Access error is generated
                   if counter is a system counter. A Counter error is generated
                   if counter does not name a valid counter.

                   counter: COUNTER
                   =>
                   value: INT64
QueryCounter       Errors: Counter

                   This request returns the current value of the given counter
                   or a generates Counter error if counter does not name a
                   valid counter.

                   wait-list: LISTofWAITCONDITION
                   Errors: Counter,Alloc,Value

                   When this request is executed, the triggers in the wait-list
                   are initialized using the wait-value and value-type fields,
                   as described in the definition of TRIGGER above. The
                   processing of further requests for the client is blocked
                   until one or more of the triggers becomes TRUE. This may
                   happen immediately, as a result of the initialization, or at
                   some later time, as a result of a subsequent SetCounter,
                   ChangeCounter or DestroyCounter request.

                   A Value error is generated if wait-list is empty.

                   When the client becomes unblocked, each trigger is checked
                   to determine whether a CounterNotify event should be
                   generated. The difference between the counter and the test
Await              value is calculated by subtracting the test value from the
                   value of the counter. If the test-type is PositiveTransition
                   or PositiveComparison, a CounterNotify event is generated if
                   the difference is at least event-threshold. If the test-type
                   is NegativeTransition or NegativeComparison, a CounterNotify
                   event is generated if the difference is at most
                   event-threshold. If the difference lies outside the range
                   for an INT64, an event is not generated.

                   This threshold check is made for each trigger in the list
                   and a CounterNotify event is generated for every trigger for
                   which the check succeeds. The check for CounterNotify events
                   is performed even if one of the triggers is TRUE when the
                   request is first executed. Note that a CounterNotify event
                   may be generated for a trigger that is FALSE if there are
                   multiple triggers in the request. A CounterNotify event with
                   the destroyed flag set to TRUE is always generated if the
                   counter for one of the triggers is destroyed.

                   counter: COUNTER
                   amount: INT64
                   Errors: Counter,Access,Value

                   This request changes the given counter by adding amount to
                   the current counter value. If the change to this counter
                   satisfies a trigger for which a client is waiting, that
                   client is unblocked and one or more CounterNotify events may
                   be generated. If the change to the counter satisfies the
ChangeCounter      trigger for an alarm, an AlarmNotify event is generated and
                   the alarm is updated. An Access error is generated if
                   counter is a system counter. A Counter error is generated if
                   counter does not name a valid counter. If the resulting
                   value for the counter would be outside the range for an
                   INT64, a Value error is generated and the counter is not
                   changed.

                   It should be noted that all the clients whose triggers are
                   satisfied by this change are unblocked, so this request
                   cannot be used to implement mutual exclusion.

                   counter: COUNTER
                   value: INT64
                   Errors: Counter,Access

SetCounter         This request sets the value of the given counter to value.
                   The effect is equivalent to executing the appropriate
                   ChangeCounter request to change the counter value to value.
                   An Access error is generated if counter names a system
                   counter. A Counter error is generated if counter does not
                   name a valid counter.

                   id: ALARM
                   values-mask: CARD32
                   values-list: LISTofVALUE
                   left">Errors: IDChoice,Counter,Match,Value,Alloc

                   This request creates an alarm and assigns the identifier id
                   to it. The values-mask and values-list specify the
                   attributes that are to be explicitly initialized. The
                   attributes for an Alarm and their defaults are:

                   Attribute Type    Default
                   trigger   TRIGGER counter    None
                                     value-type Absolute
                                     value      0
                                     test-type  PositiveComparison
                   delta     INT64   1           
                   events    BOOL    TRUE        

                   The trigger is initialized as described in the definition of
                   TRIGGER, with an error being generated if necessary.

                   If the counter is None, the state of the alarm is set to
                   Inactive, else it is set to Active.

                   Whenever the trigger becomes TRUE, either as a result of
CreateAlarm        this request or as the result of a SetCounter,
                   ChangeCounter, DestroyCounter, or ChangeAlarm request, an
                   AlarmNotify event is generated and the alarm is updated. The
                   alarm is updated by repeatedly adding delta to the value of
                   the trigger and reinitializing it until it becomes FALSE. If
                   this update would cause value to fall outside the range for
                   an INT64, or if the counter value is None, or if the delta
                   is 0 and test-type is PositiveComparison or
                   NegativeComparison, no change is made to value and the alarm
                   state is changed to Inactive before the event is generated.
                   No further events are generated by an Inactive alarm until a
                   ChangeAlarm or DestroyAlarm request is executed.

                   If the test-type is PositiveComparison or PositiveTransition
                   and delta is less than zero, or if the test-type is
                   NegativeComparison or NegativeTransition and delta is
                   greater than zero, a Match error is generated.

                   The events value enables or disables delivery of AlarmNotify
                   events to the requesting client. The alarm keeps a separate
                   event flag for each client so that other clients may select
                   to receive events from this alarm.

                   An AlarmNotify event is always generated at some time after
                   the execution of a CreateAlarm request. This will happen
                   immediately if the trigger is TRUE, or it will happen later
                   when the trigger becomes TRUE or the Alarm is destroyed.

                   id: ALARM
                   values-mask: CARD32
                   values-list: LISTofVALUE
                   Errors: Alarm,Counter,Value,Match

                   This request changes the parameters of an Alarm. All of the
                   parameters specified for the CreateAlarm request may be
                   changed using this request. The trigger is reinitialized and
                   an AlarmNotify event is generated if appropriate, as
ChangeAlarm        explained in the description of the CreateAlarm request.

                   Changes to the events flag affect the event delivery to the
                   requesting client only and may be used by a client to select
                   or deselect event delivery from an alarm created by another
                   client.

                   The order in which attributes are verified and altered is
                   server-dependent. If an error is generated, a subset of the
                   attributes may have been altered.

                   alarm: ALARM
                   Errors: Alarm

DestroyAlarm       This request destroys an alarm. An alarm is automatically
                   destroyed when the creating client is closed down if the
                   close-down mode is Destroy. When an alarm is destroyed, an
                   AlarmNotify event is generated with a state value of
                   Destroyed.

                   alarm: ALARM
                   =>
                   trigger: TRIGGER
                   delta: INT64
QueryAlarm         events: ALARMEVENTMASK
                   state: ALARMSTATE
                   Errors: Alarm

                   This request retrieves the current parameters for an Alarm.

                   client-resource: XID
                   priority: INT32
                   Errors: Match

                   This request changes the scheduling priority of the client
                   that created client-resource. If client-resource is None,
                   then the priority for the client making the request is
                   changed. A Match error is generated if client-resource is
                   not None and does not name an existing resource in the
                   server. For any two priority values, A and B, A is higher
                   priority if and only if A is greater than B.

                   The priority of a client is set to 0 when the initial client
                   connection is made.

SetPriority        The effect of different client priorities depends on the
                   particular implementation of the extension, and in some
                   cases it may have no effect at all. However, the intention
                   is that higher priority clients will have their requests
                   executed before those of lower priority clients.

                   For most animation applications, it is desirable that
                   animation clients be given priority over nonrealtime
                   clients. This improves the smoothness of the animation on a
                   loaded server. Because a server is free to implement very
                   strict priorities, processing requests for the highest
                   priority client to the exclusion of all others, it is
                   important that a client that may potentially monopolize the
                   whole server, such as an animation that produces continuous
                   output as fast as it can with no rate control, is run at low
                   rather than high priority.

                   client-resource: XID
                   =>
                   priority: INT32
                   Errors: Match

GetPriority        This request returns the scheduling priority of the client
                   that created client-resource. If client-resource is None,
                   then the priority for the client making the request is
                   returned. A Match error is generated if client-resource is
                   not None and does not name an existing resource in the
                   server.

                   drawable: DRAWABLE
                   id: FENCE
                   initially-triggered: BOOL
                   Errors: IDChoice,Alloc
CreateFence
                   This request creates a fence on the screen associated with
                   drawable and assigns the specified id to it. The fence is in
                   the triggered state iff initially-triggered is TRUE. There
                   are no clients waiting on the fence.

                   fence: FENCE
                   Errors: Fence

                   This request puts the given fence in the triggered state
                   after all rendering from previous requests that affects
                   resources owned by the fence's screen has completed. This
                   includes requests from other clients if those requests have
                   been dispatched. This request has no visible effects if the
                   fence was already in the triggered state. A Fence error is
TriggerFence       generated if fence does not name a valid fence.

                   Note that the given fence's state is not necessarily
                   directly modified by this request. The state change need
                   only be queued to occur after the required rendering has
                   completed. Clients should take care to not assume the fence
                   will be in the triggered state in subsequent requests, such
                   as those that operate on the given fence immediately.
                   AwaitFence should first be issued if subsequent requests
                   require the fence to be in the triggered state.

                   fence: FENCE
                   Errors: Fence,Match

                   This request immediately puts the given fence in the not
                   triggered state. A Match error is generated if the fence is
                   not in the triggered state. A Fence error is generated if
ResetFence         fence does not name a valid fence.

                   See the warnings above regarding TriggerFence's delayed
                   effect. In particular, a TriggerFence request immediately
                   followed by a ResetFence request is likely to result in a
                   Match error. An AwaitFence request should be issued between
                   the two.

                   fence: FENCE
                   Errors: Fence

                   This request destroys the given fence. All clients waiting
DestroyFence       on this fence are released. A fence is destroyed
                   automatically when the connection to the client that created
                   the fence is closed if the close-down mode is DestroyAll. A
                   Fence error is generated if fence does not name a valid
                   fence.

                   fence: FENCE
                   =>
                   triggered: BOOL
QueryFence         Errors: Fence

                   This request returns TRUE if the given fence is triggered,
                   or FALSE if it is not triggered. A Fence error is generated
                   if fence does not name a valid fence.

                   fence-list: LISTofFENCE
                   Errors: Fence,Alloc

                   When this request is executed, the processing of further
AwaitFence         requests for the client is blocked until one or more of the
                   fences in fence-list reaches the triggered state. If any of
                   the fences are already in the triggered state, request
                   processing resumes immediately. A Fence error is generated
                   if any member of fence-list does not name a valid fence.

Events

              counter: COUNTER
              wait-value: INT64
              counter-value: INT64
              time: TIME
              count: CARD16
              destroyed: BOOL

              CounterNotify events may be generated when a client becomes
              unblocked after an Await request has been processed. The
CounterNotify wait-value is the value being waited for, and counter-value is
              the actual value of the counter at the time the event was
              generated. The destroyed flag is TRUE if this request was
              generated as the result of the destruction of the counter and
              FALSE otherwise. The time is the server time at which the event
              was generated.

              When a client is unblocked, all the CounterNotify events for the
              Await request are generated contiguously. If count is 0, there
              are no more events to follow for this request. If count is n,
              there are at least n more events to follow.

              alarm: ALARM
              counter-value: INT64
              alarm-value: INT64
              state: ALARMSTATE
              time: TIME

AlarmNotify   An AlarmNotify event is generated when an alarm is triggered.
              alarm-value is the test value of the trigger in the alarm when it
              was triggered, counter-value is the value of the counter that
              triggered the alarm, and time is the server time at which the
              event was generated. The state is the new state of the alarm. If
              state is Inactive, no more events will be generated by this alarm
              until a ChangeAlarm request is executed, the alarm is destroyed,
              or the counter for the alarm is destroyed.

Chapter 2. Encoding

Table of Contents

Encoding New Types
Encoding Errors
Encoding Requests
Encoding Events

Please refer to the X11 Protocol Encoding document as this section uses
syntactic conventions established there and references types defined there.

The name of this extension is "SYNC".

Encoding New Types

The following new types are used by the extension.

ALARM: CARD32
ALARMSTATE:
       0         Active
       1         Inactive
       2         Destroyed
COUNTER: CARD32
INT64: 64-bit signed integer
SYSTEMCOUNTER:
       4         COUNTER                 counter
       8         INT64                   resolution
       2         n                       length of name in bytes
       n         STRING8                 name
       p                                 pad,p=pad(n+2)
TESTTYPE:
       0         PositiveTransition
       1         NegativeTransition
       2         PositiveComparison
       3         NegativeComparison
TRIGGER:
       4         COUNTER                 counter
       4         VALUETYPE               wait-type
       8         INT64                   wait-value
       4         TESTTYPE                test-type  VALUETYPE:
       0         Absolute
       1         Relative
WAITCONDITION:
       20        TRIGGER                 trigger
       8         INT64                   event threshold
FENCE: CARD32

An INT64 is encoded in 8 bytes with the most significant 4 bytes first followed
by the least significant 4 bytes. Within these 4-byte groups, the byte ordering
determined during connection setup is used.

Encoding Errors

Counter
        1    0            Error
        1    Base + 0     code
        2    CARD16       sequence number
        4    CARD32       bad counter
        2    CARD16       minor opcode
        1    CARD8        major opcode
        21                unused
Alarm
        1    0            Error
        1    Base + 1     code
        2    CARD16       sequence number
        4    CARD32       bad alarm
        2    CARD16       minor opcode
        1    CARD8        major opcode
        21                unused
Fence
        1    0            Error
        1    Base + 2     code
        2    CARD16       sequence number
        4    CARD32       bad fence
        2    CARD16       minor opcode
        1    CARD8        major opcode
        21                unused

Encoding Requests

Initialize
        1    CARD8        major opcode
        1    0            minor opcode
        2    2            request length
        1    CARD8        major version
        1    CARD8        minor version
        2                 unused
=>
        1    1            Reply
        1                 unused
        2    CARD16       sequence number
        4    0            reply length
        1    CARD8        major version
        1    CARD8        minor version
        2                 unused
        20                unused

ListSystemCounters
        1    CARD8                  major opcode
        1    1                      minor opcode
        2    1                      request length
=>
        1    1                      Reply
        1                           unused
        2    CARD16                 sequence number
        4    0                      reply length
        4    INT32                  list length
        20                          unused
        4n   list of SYSTEMCOUNTER  system counters

CreateCounter
        1    CARD8                  major opcode
        1    2                      minor opcode
        2    4                      request length
        4    COUNTER                id
        8    INT64                  initial value

DestroyCounter
        1    CARD8                  major opcode
        1    6                      minor opcode^[1]
        2    2                      request length
        4    COUNTER                counter
=>
        1    1                      Reply
        1                           unused
        2    CARD16                 sequence number
        4    0                      reply length
        8    INT64                  counter value
        16                          unused

Await
        1    CARD8                  major opcode
        1    7                      minor opcode^[2]
        2    1 + 7*n                request length
        28n  LISTofWAITCONDITION    wait conditions

ChangeCounter
        1    CARD8                  major opcode
        1    4                      minor opcode^[3]
        2    4                      request length
        4    COUNTER                counter
        8    INT64                  amount

SetCounter
        1    CARD8                  major opcode
        1    3                      minor opcode^[4]
        2    4                      request length
        4    COUNTER                counter
        8    INT64                  value

CreateAlarm
        1    CARD8                  major opcode
        1    8                      minor opcode
        2    3+n                    request length
        4    ALARM                  id
        4    BITMASK                values mask

             #x00000001             counter
             #x00000002             value-type
             #x00000004             value
             #x00000008             test-type
             #x00000010             delta
             #x00000020             events

        4n   LISTofVALUE            values

VALUES
        4    COUNTER                counter
        4    VALUETYPE              value-type
        8    INT64                  value
        4    TESTTYPE               test-type
        8    INT64                  delta
        4    BOOL                   events

ChangeAlarm
        1    CARD8                  major opcode
        1    9                      minor opcode
        2    3+n                    request length
        4    ALARM                  id
        4    BITMASK                values mask
             encodings as for CreateAlarm
        4n   LISTofVALUE            values
             encodings as for CreateAlarm

DestroyAlarm
        1    CARD8        major opcode
        1    11           minor opcode^[5]
        2    2            request length
        4    ALARM        alarm

QueryAlarm
        1    CARD8        major opcode
        1    10           minor opcode^[6]
        2    2            request length
        4    ALARM        alarm
=>
        1    1            Reply
        1                 unused
        2    CARD16       sequence number
        4    2            reply length
        20   TRIGGER      trigger
        8    INT64        delta
        1    BOOL         events
        1    ALARMSTATE   state
        2                 unused

SetPriority
        1    CARD8        major opcode
        1    12           minor opcode
        2    3            request length
        4    CARD32       id
        4    INT32        priority

GetPriority
        1    CARD8        major opcode
        1    13           minor opcode
        2    1            request length
        4    CARD32       id
=>
        1    1            Reply
        1                 unused
        2    CARD16       sequence number
        4    0            reply length
        4    INT32        priority
        20                unused

CreateFence
        1    CARD8        major opcode
        1    14           minor opcode
        2    4            request length
        4    DRAWABLE     drawable
        4    FENCE        id
        1    BOOL         initially triggered
        3                 unused

TriggerFence
        1    CARD8        major opcode
        1    15           minor opcode
        2    2            request length
        4    FENCE        id

ResetFence
        1    CARD8        major opcode
        1    16           minor opcode
        2    2            request length
        4    FENCE        id

DestroyFence
        1    CARD8        major opcode
        1    17           minor opcode
        2    2            request length
        4    FENCE        id

QueryFence
        1    CARD8        major opcode
        1    18           minor opcode
        2    2            request length
        4    FENCE        id
=>
        1    1            Reply
        1                 unused
        2    CARD16       sequence number
        4    0            reply length
        1    BOOL         triggered
        23                unused

AwaitFence
        1    CARD8        major opcode
        1    19           minor opcode
        2    1 + n        request length
        4*n  LISTofFENCE  wait conditions


Encoding Events

CounterNotify
        1    Base + 0     code
        1    0            kind
        2    CARD16       sequence number
        4    COUNTER      counter
        8    INT64        wait value
        8    INT64        counter value
        4    TIME         timestamp
        2    CARD16       count
        1    BOOL         destroyed
        1                 unused

AlarmNotify
        1    Base + 1     code
        1    1            kind
        2    CARD16       sequence number
        4    ALARM        alarm
        8    INT64        counter value
        8    INT64        alarm value
        4    TIME         timestamp
        1    ALARMSTATE   state
        3                 unused


━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

^[1] A previous version of this document gave an incorrect minor opcode

^[2] A previous version of this document gave an incorrect minor opcode.

^[3] A previous version of this document gave an incorrect minor opcode.

^[4] A previous version of this document gave an incorrect minor opcode.

^[5] A previous version of this document gave an incorrect minor opcode.

^[6] A previous version of this document gave an incorrect minor opcode.

