Chapter 9

X Synchronization Extension

This Chapter explains X Synchronization Extension. This extended function is necessary to allow synchronization to be implemented among client systems in the multimedia application fields handling video images and voices. This extended function adopted as one of the X Consortium standards.

9.1 SYNCHRONIZATION

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 due to the need for round-trip requests which keep the client and server synchronized.

The Synchronization extension provides primitives which allow synchronization between clients to take place entirely within the X server. This removes any error introduced by the network and make it possible to synchronize clients on different hosts running different operation system. This is important for multi-media applications where audio, video and graphics data streams are being synchronized. The extension also provides internal timer 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.

9.2 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 and Alarm to the set of resources managed by the server. A counter has a 64-bit integer value which may be increased or decreased by client requests or by the server internally. A client can block by sending an Await request which waits until on of a set of synchronization conditions, called TRIGGERs, becomes TRUE.

The CreateCounter request allows a client to create a Counter which 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, which 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 which advances with the server time as defined by the core protocol, and it may also provide counters which advance with the real-world time or which change each time the CRT screen is refreshed. Other extensions may provide their own extension-specific system counters.

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

9.3 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.

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 which 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 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 which 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 which initialized the trigger will return a Value error. If counter is None and the value-type is Relative, the request which 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 form 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 form a value greater than the test value to a value less than or equal to the test value. If the test-tvpe 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 which 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 System Counter. The name field is the textual name of the counter which identifies the counter to the client. The counter field is the client-side handle which should be used in requests which 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, amy 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-btis 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.

9.4 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.

9.5 REQUESTS

Initialize

version-major,version-minor: CARD8

version-major,version-minor: CARD8
This request must be executed before nay 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 which 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 depending of the version number supplied by that client. This request should only be executed once for each client connection.
Given two different versions of the SYNC protocol, v1 an v2, v1 is compatible with v2 if and only if v1.version_major=v2.version_majorand 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 0 of the SYNC protocol.

ListSystemCounters

system-counters: LISTofSYSTEMCOUNTER

Errors: Alloc

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

Createcounter

id: COUNTER
initial-value: INT64

Errors: ID Choice, Alloc

This request creates a counter and assigns the identifier id to it. The counter value is initialized to initial value and there are no clients waiting on the counter.

Destroy Counter

counter: COUNTER

Erros: Counter,Access

This request destroys the given counter and sets the counter fields for all triggers which 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 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.

QueryCounter

counter: COUNTER

value: INT64

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.

Await

wait-lisr. 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 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 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 on 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 i 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.

ChangeCounter

counter: COUNTER
amount INT64

Erros: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 client is waiting, that client is unblocked and one or more CounterNotify events may be generated . If the change to the counter satisfies the 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.

Setcounter

counter: COUTNER
value: INT64

Errors: Counter,Access

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.

CreateAlarm

id: ALARM
values-mask: CARD32
values-list LISTofVALUE

Erros: ID Choice , 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 which are to be explicitly initialized. The attributes for an Alarm and their defaults are:

Attribute	Type	Default
trigger	RIGGER	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 this request or as the result of a SetCounter, ChangeCounter, DestoryCounter 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 re-initializing it until it becomes FASE. If this update would cause value to fall outside the range for an INT64, or if the countervalue is None, orif 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 DestoyAlarm 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 form 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.

ChangeAlarm

id: ALARM
values-mask: CARD32
values-list LISTofVALUE

Erros: 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 re-initialized and an AlarmNotify event is generated if appropriate, as 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 sued by a client to select or de-select 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.

Destroy Alarm

alarm: ALARM

Errors: Alarm

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.

QueryAlarm

alarm: ALARM

trigger: TRIGGER
delta: INT64
events: ALARMEVENTMASK
state: ALARMSTATE

Errors: Alarm

This request retrieves the current parameters for an Alarm.

SetPriority

client-resource: XID
priority: INT32

Errors: Match

This request changes the scheduling priority of the client which 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 no None and does not name an existing resource in the server. For any two priority value, A an dB, 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.

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 application, it is desirable that animation clients are given priority over non-real-time 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 other, it is important that a client which may potentially monopolize the whole server, such as an animation which produces continuous output as fast as it can with no rate control, is run at low rather than high priority.

GetPriority

client-resource: XID

priority: INT32

Errors: Match

This request returns the scheduling priority of the client which 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 clientresource is not None and does not name an existing resource in the server.

9.6 EVENTS

CounterNotify

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. wait-value is the value being waited for an 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. name 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 continuously. If count is n, there are at least n more events to follow.

AlarmNotify

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

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 which triggered the alarm and time is the server time at which the event was generated. 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.

9.7 ENCODING

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".

9.7.1 New Types

The following new types are sued 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	eventthreshold

An INT64 is encode 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.

9.7.2 Errors

Counter

1	0	Error
1	Base + 0	code
2	CARD16	sequence number
4	CARD32	badcounter
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

9.7.3 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	variable	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

Destroy Counter

1	CARD8	major opcode
1	3	minor opcode
2	2	request length
4	COUNTER	counter

Query Counter

1	CARD8	major opcode
1	4	minor opcode
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	5
2	1+7*n	request length
28n	LIST of WAITCONDITION	wait conditions

ChangeCounter

1	CARD8	major opcode
1	6	minor opcode
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

Destroy Alarm

1	CARD8	major opcode
1	10	minor opcode
2	2	request length
4	ALARM	alarm

QueryAlarm

1	CARD8	major opcode
1	11	minor opcode
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

9.7.4 Events

CounterNotify

1	Base+0	code
1	0	kind
2	CARD16	sequenced number
4	COUNTER	counter
8	INT64	wait value
8	INT64	countervalue
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

9.8 C LANGUAGE BINDING

The C routines provide direct access to the protocol and add no additional semantics.

The include file for this extension is <x 11/extensions/sync.h>.

Most of the names in the language binding are derived from the protocol names by prepending XSync to the protocol name and changing the capitalization.

9.8.1 C Functions

Most of the following functions generate SYNC protocol requests.

Status
XSyncQueryExtension (Display * dpy , int * event_base_return , int * error_base return )

If dpy supports the SYNC extension, this function returns True, sets *event_base_return to the event number for the first SYNC event, and sets *error_base_return to the error number for the first SYNC error. If dpy does not support the SYNC extension, this function returns False.

Status
XSyncInirtialize (Display * dpy , int * major_version_return , int * minor_version_return )

Set *major_verison_return and *minor_version_return to the major/minor SYNC protocol version supported by the server. If the XSync library is compatible with the version returned by the sever, this function returns True. If dpy does not support the SYNC extension, or if there was an error during communication with the server, or if the server and library protocol versions are incompatible, this function returns False. The only XSync function that may be called before this function is XSyncQueryExtension. If a client violates this rule, the effects of all XSync calls that it makes are undefined.

XSyncSystemCounter *
XSyncListSystemCounters (Display * dpy, int * n_counters_return)

Returns a pointer to an array of system counters supported by the display, and sets *n_counters_return to the number of counters in the array. The array should be freed with XSyncFreeSystemCounterList. If dpy does not support the SYNC extension, or if there was an error during communication with the server, or if the server does not support any system counters, this function returns NULL.

XSync System Counter has the following fields:

void
XSyncFreeSystemCounterList ( XSync System counter * list)

Frees the memory associated with the system counter list returned by XSync ListSystemCounters.

Xsynccounter
XSync CreateCounter (Display * dpy, XSyncvalue initial_value)

Creates a counter on the dpy with the given initial_value and returns the counter ID. Returns None if dpy does not support the SYNC extension.

Status
XSync set counter (Display * dpy ,XSyncCounter counter, XSyncValue value )

Sets counter to value. Returns False if dpy does not support the SYNC extension, else turns True.

Status
XSyncChangeCounter (Display * dpy, XSyncCounter counter ,XSyncValue value )

Sets counter to value. Returns False if dpy does not support the SYNC extension, else returns True.

Status
XSyncChangeCounter (Display * dpy, XSyncCounter counter, XSyncValue value)

Adds value to counter. Returns False if dpy does not support the SYNC extension, else returns True.

Status
XSyncDestroyCounter (Display * dpy, XSyncCounter counter)

Destroys counter. Retums False if dpy does not support the SYNC extension, else returns True.

Status
XSync Query Counter (display * dpy, XSynccounter counter, XSyncvalue * value_return )

Sets *value_return to the current value of counter. Returns False if there was an error during communication with the server, or if dpy does not support the SYNC extension, else returns True.

Status
XSyncAwait (display * dpy , XSyncWaitCondition * wait_list , int n_conditions )

Awaits on the conditions in wait_list . n_conditions is the number of wait conditions in wait_list. Returns False if dpy does not support the SYNC extension, else returns True. The await is processed asynchronously by the server; this function always returns immediately after issuing the request.

XSyncWaitCondition has the following fields:

XSyncvalueType can be either XSyncAbsolute or XSyncRelative.

XSyncTestType can be one of XS ync PositiveTransition,
XSyncNegativeTransition, XS ync PositiveComparison, or
XSyncNegativeComparison.

XSyncAlarm
XSyndCreateAlarm (Display * dpy , unsigned long values_mask , XSyncAlarmAttributes * values )

Creates an alarm and returns the alarm ID. Returns None if the display does not support the SYNC extension. values_mask and values specify the alarm attributes.

XSyncAlarmAttributes has the following fields. The attributes_mask column specifies the symbol that the caller should OR into values_mask to indicate that the value for the corresponding attribute was actually supplied. Default values are used for all attributes that do not have their attribute_mask OR'ed into value_mask . See the protocol description for CreateAlarm for the defaults.

Status
XSyncDestroyAlarm (display * dpy, XSyncAlarm alarm )

Destroys alarm . Returns False if dpy does not support he SYNC extension, else returns True.

Status
XSyncQueryAlarm (Display * dpy , XSyncAlarm alarm , XSyncAlarmAttributes * values_return)

Sets *values_return to the alarm's attributes. Returns False if there was an error during communication with the server, or if dpy does not support the SYNC extension, else returns True.

Status
XSyncChangeAlarm (Display * dpy , XSyncAlarm alarm , unsigned long values_mask , XSyncAalrmAttributes * value )

Changes alarm's attributes. The attributes to change are specified as in XSyncCreateAlarm. Returns False if dpy does not support he SYNC extension, else returns True.

Status
XSyncSetPriorty (Display * dpy , XID client_resource_id , int priority)

Sets the priority of the client owning client-resource-id to priority. If client_resource_id is None, sets the caller's priority. Returns False if dpy does not support the SYNC extension, else returns True.

Status
XSyncGetPriority (Display * dpy , XID client_resource_id , int * return_priority )

Sets *return priority to the priority of the client owning client_resource_id . If client_resource_id is None, sets *return_priority to the caller's priority. Returns False if there was an error during communication with the server, or if dpy does not support the SYNC extension, else returns True.

9.8.2 C Macros/Functions

The following procedures manipulate 64 bit values. They are defined both as macros and as functions. By default, the macro form is used. To sue the function form, #undef the macro name to uncover the function.

void
XSyncIntToValue (XSyncvalue *pv, int i)

Converts i to an XSyncvalue and store it in *pv. Performs sign extension (*pv will have the same sign as i.)

void
XSyncIntsToValue (XSyncvalue *pv, unsigned int low, int high )

Stores low int he low 32 bits of *pv and high in the high 32 bits of *pv.

Bool
XSyncValueGreaterThan (xsyncvalue a, XSyncValue b )

Returns True if a is greater than b , else returns False.

Bool
XSyncValueLessThan (XSyncvalue a, XSyncvalue b )

Returns True if a is less than b , else returns False.

Bool
XSyncValueGreaterOrEqual (XSyncvalue a, XSyncValue b )

Returns True if a is greater than or equal to b , else returns False.

Bool
XSyncValueLessOrEqual (xsyncvalue a, XSyncValue b)

Returns True if a is less than or equal to b ,

Bool
XSyncValueEqual (XSyncvalue a, XSyncvalue b)

Returns True if a is equal to b, else returns False.

Bool
XSyncValue Is Negative (XSyncValue v)

Returns True if v is negative, else returns False.

Bool
XSyncValueIszero (XSyncValue v)

Return True if v is zero, else returns False.

Bool
XSyncValueIsPostive (XSyncValue v)

Returns True if v is positive, else returns False.

unsigned int
XSyncValueLow32 (XSyncValue v)

Returns the low 32 bits of v.

int
XSyncValueHigh32 (XSyncValue v)
Returns the high 32 bits of v.

void
XSyncValueAdd (XSyncValue * presult , XSyncvalue a, XSyncvalue b, Bool * poverflow )

Adds a to b and stores the result in *presult . If the result could not fit in 64 bits, *poverflow is set to True else it is set to False.

void
XSyncvalueSubtract (XSyncvalue * presult , XSyncvalue a, XSyncvalue b, Bool * poverflow )

Subtracts b from a and stores the result in *presult . If the result could not fit in 64 bits, overflow is set to True else it is set to False.

void
XSyncmaxvalue ( XSyncValue * pv)
Set *pv to the maximum value expressible in 64 bits.

void
XSyncMinValue ( XSyncValue * pv)

Sets *pv to the minimum value expressible in 64 bits.

9.8.3 Events

Let event_base be the value event_base_return as defined in the function XSyncQueryextension.

An XSynCounterNotifyEvent's type field has the value event_base + XSynccounterNotify. The fields of this structure are:

An XSyncAlarmNotifyEvent's type field has the value event_base + XSyncAlarmNotify. The fields of this structure are:

9.8.4 Errors

Let error_base be the value error_base_return as defined in the function XSyncQueryextension.

An XSyncAlarmError's error_code field has the value error_base + XsyncBadAlarm. The fields of this structure are:

An XSynCounterError's error_co has the value error_base + XSyncsadCounter. The fields of this structure are: