U.S. patent application number 12/821306 was filed with the patent office on 2011-07-28 for message passing framework for audio/video streaming in a topology of devices.
Invention is credited to Srikanth Kambhatla.
Application Number | 20110185026 12/821306 |
Document ID | / |
Family ID | 44309012 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110185026 |
Kind Code |
A1 |
Kambhatla; Srikanth |
July 28, 2011 |
Message Passing Framework for Audio/Video Streaming in a Topology
of Devices
Abstract
Resources may be managed in a topology for audio/video
streaming. The topology includes audio/video sources and sinks and
intervening branch devices. Messages between these sources, sinks,
and branch devices may be used for resource management.
Inventors: |
Kambhatla; Srikanth;
(Portland, OR) |
Family ID: |
44309012 |
Appl. No.: |
12/821306 |
Filed: |
June 23, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61298936 |
Jan 28, 2010 |
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Current U.S.
Class: |
709/206 |
Current CPC
Class: |
G09G 2352/00 20130101;
G09G 5/006 20130101; G06F 13/4027 20130101; G06F 13/4221 20130101;
G09G 2350/00 20130101; H04L 43/0882 20130101; G09G 2370/10
20130101; H04L 65/1089 20130101; G09G 2370/20 20130101; G06F 3/1423
20130101; H04L 65/4069 20130101; G09G 2370/04 20130101 |
Class at
Publication: |
709/206 |
International
Class: |
G06F 15/16 20060101
G06F015/16 |
Claims
1. A method comprising: enabling any device in a topology of
devices, including devices that source and sink video data, to take
an action specified in a message depending on a type indicator
within the message.
2. The method of claim 1 including enabling each device in the
topology that receives a message sent from a source to a sink to
take action depending on the nature of the indicator in the
message.
3. The method of claim 1 including determining whether the message
indicator indicates actions are done on the way to the destination
and, if so, performing any actions required upon receipt of the
message.
4. The method of claim 1 including determining whether the message
indicator indicates actions are performed only on the
acknowledgement from the ultimate destination and, if so, only
performing any actions upon receipt of an acknowledgment.
5. The method of claim 1 including determining whether the
message's indicator indicates only the destination performs actions
and, if so, determining if the receiving device is the destination
and, if so, and only if so, performing the action in the
message.
6. The method of claim 5 including, if the device is not the
destination of the message, forwarding the message along a path to
the destination.
7. The method of claim 1 including, upon completion of an action in
the message, providing an acknowledgement back to the source.
8. The method of claim 1 including implementing path training in
response to a message that requires action upon receipt of the
message.
9. The method of claim 1 including implementing path training using
a message which requires action only upon receipt of the
acknowledgement from the destination of the message.
10. The method of claim 1 including receiving messages which
require action by devices within the topology of devices that
source and sink audio and video data depending on the type of
message and whether or not the device is the destination of the
message.
11. A computer readable medium storing instructions for execution
by a processor in a device in a topology of devices including a
source and sink of video data to: receive a message with an action
to be performed; determine the message type; and based on the
message type, perform an action specified in the message.
12. The medium of claim 11 further storing instructions to
determine whether the message type is one in which actions are to
be done on the way to the destination and, if so, perform any
actions required upon receipt of the message.
13. The medium of claim 11 further storing instructions to
determine whether the message is of the type in which actions are
performed only on the acknowledgement from the ultimate destination
and, if so, only perform any actions upon receipt of an
acknowledgement.
14. The medium of claim 11 further storing instructions to
determine whether the message's type is one in which only the
destination performs actions and, if so, determine if the receiving
device is the destination and, if so, and only if so, performing
the action indicated in the message.
15. The medium of claim 14 further storing instructions to forward
the message along a path to the destination if the device is not
the destination of the message.
16. The medium of claim 11 further storing instructions to provide
an acknowledgement back to the source upon completion of an action
indicated in the message.
17. The medium of claim 11 further storing instructions to
implement path training in response to a message that requires
action upon receipt of the message.
18. The medium of claim 11 further storing instructions to
implement path training using a message that requires action only
upon receipt of an acknowledgement from the destination of the
message.
19. The medium of claim 11 further storing instructions to receive
messages which require action by devices within the topology of
devices that source and sink video data depending on the type of
message and whether or not the receiving device is the destination
of the message.
20. The medium of claim 11 further storing instructions to enable
messages that can be acted upon by any device along the path of the
message between the source and the destination of the message.
21. An apparatus comprising: a receiver to receive messages from a
source in a topology of devices, said source to source video data
to a sink in the topology; a transmitter to transmit video data
toward the sink; and a unit to receive a message from a source with
an action to be performed, determine the message type, determine
whether to perform an action specified in the message upon receipt
of the message, upon receipt of an acknowledgement from the
destination of the message, or to not perform the action at
all.
22. The apparatus of claim 21, said unit to determine whether the
message type is one in which actions are to be done on the way to
the destination and, if so, perform the action in the message upon
receipt of the message.
23. The apparatus of claim 21, said unit to determine whether the
message is of the type in which actions are to be performed only on
the acknowledgement from the ultimate destination and, if so, only
perform the actions upon receipt of the acknowledgement.
24. The apparatus of claim 21, said unit to determine whether the
message's type is one in which only the destination of the message
performs the action and, if so, determine if the apparatus is the
destination and, if so, and only if so, perform the action
indicated in the message.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to provisional application
Ser. No. 61/298,936, filed on Jan. 28, 2010, hereby incorporated by
reference herein.
BACKGROUND
[0002] This relates generally to devices that source and sink video
and audio data.
[0003] DisplayPort is a digital audio/video interconnect standard
of the Video Electronic Standards Association (VESA). It allows
video and audio to be coupled from a computer to a video display or
an audio playback system. The DisplayPort connector supports 1, 2,
or 4 data pairs in a main link that also carries clock and optional
audio signals with symbol rates of 1.62, 2.7, or 5.4 gigabits per
second. A 1.1 standard was approved in May 2006 and in 2009 a 1.2
standard, with increased data rates, was announced. The DisplayPort
1.2 standard doubles the bandwidth of the 1.1 standard.
[0004] With the DisplayPort 1.2 standard, two WQXGA monitors may
sink audio/video data from a single source link or four WUXGA
monitors may sink data from a single source link. In addition, the
1.2 standard allows a higher speed AUX which may be used for
Universal Serial Bus (USB) peripheral device data transfer,
microphone audio transfer, or camera video transfer, to mention a
few applications.
[0005] Display or sink devices can be connected to source devices,
such as personal computers or consumer electronic devices, either
directly or through what are called branch devices. Many types of
branch devices exist including repeaters that repeat audio or video
information, converters that convert audio or video information
from one format to another, replicaters, which reproduce the data,
and concentrators that take streams from two or more source devices
as inputs and transmit them on its downstream links. Interface
standards, such as DisplayPort 1.2, allow multiple streams on one
link; in such cases, these two or more input streams may be
transmitted onto a single downstream link. Some concentrators may
operate in a switched fashion, i.e. only one selected source may
transmit at a time.
[0006] Together, the source, sink, and branch devices form a
topology in which a given source may be streaming video to one or
more sinks through zero or more branch devices. Active video data
flows through links connecting various device types. Each link is
constrained by its bandwidth and the number of streams that it
supports. A sink will have a limited number of audio and video
endpoints to render the stream. Thus, based on the topology, there
may be contention for the available video or audio resources.
[0007] One such topology, shown in FIG. 1, may include two sources
and five sinks, as indicated. A source number 1 wants to stream
video to sink number 1 and source number 2 wants to stream video to
sink number 2, the link between branch number 2 and branch number 3
is common to both paths. Thus, issues may arise at the source with
respect to this contention, including how much bandwidth is
available in that or any other link along the path. Another issue
is how resources on the path can be reserved. Still another issue
is how many audio/visual streams can be driven. Other issues
include how access to shared resources can be managed and how
errors can be communicated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic depiction of a audio/video
distribution topology in accordance with one embodiment;
[0009] FIG. 2 is a sequence chart for enumeration, commit and
release in accordance with one embodiment;
[0010] FIG. 3 is a schematic depiction for one embodiment of a
branch device;
[0011] FIG. 4 is a flow chart for enumeration software in
accordance with one embodiment;
[0012] FIG. 5 is a message sequence chart in accordance with one
embodiment;
[0013] FIG. 6 is a sequence chart for enumeration of path resources
in accordance with one embodiment;
[0014] FIG. 7 is a sequence chart showing how various display
configurations can be established for the topology shown in FIG.
6;
[0015] FIG. 8 is a depiction of a potential mapping between two
sources and two sinks in accordance with one embodiment;
[0016] FIG. 9 is a flow chart for one embodiment;
[0017] FIG. 10 is a flow chart for one embodiment;
[0018] FIG. 11 shows a message sequence in accordance with one
embodiment;
[0019] FIG. 12 is an up action path message sequence in accordance
with one embodiment;
[0020] FIG. 13 is a mapping of destination sequences in accordance
with one embodiment;
[0021] FIG. 14 is a message sequence chart for an uplink action
path message in accordance with one embodiment;
[0022] FIG. 15 is a depiction of connections between source and
branch devices in accordance with one embodiment;
[0023] FIG. 16 is a depiction of multiple source and branch devices
according to one embodiment;
[0024] FIG. 17 is a depiction of a topology with two video end
points in accordance with one embodiment; and
[0025] FIG. 18 is a flow chart for one embodiment.
DETAILED DESCRIPTION
[0026] In accordance with some embodiments, specific messages may
be exchanged between devices that source and sink video and audio
data. Coordinated action may be taken by devices along a path
between source and sink devices in response to those messages.
Messages may be sent to a targeted destination that is specified by
its address. The messages ENUM_PATH_RESOURCES,
COMMIT_PATH_RESOURCES, and RELEASE_PATH_RESOURCES may be used, as
indicated in FIG. 2. These messages can be sent on the AUX channel
in the DisplayPort specification, for example.
[0027] Address spaces are generated before message transmission.
Each source 10 sends ENUM_PATH_RESOURCE message 18 to the desired
sink 16 to enumerate the main link bandwidth and the number of
streams. The branch device 14, just upstream of the desired sink
16, responds with the available bandwidth (BW=x) and number of
streams (# STREAMS=s), as indicated at 20. Before this reply is
propagated further upstream, the upstream branch 12 alters the
available bandwidth (BW=x') and stream number (# STREAMS=s') from
the downstream branch 14 to reflect what is achievable from the
downstream path, as indicated at 22.
[0028] Eventually, the source 10 gets the path resources. The
message is sent on a control bus (such as AUX on DisplayPort), but
the query is for main link resources. There is no reservation of
bandwidth on the control bus and control messages are exchanged
between devices in the topology, even as the main link resource are
completely spoken for by one or two sources.
[0029] As part of the processing of the message, each device may
need to train the main link along the specified path to determine
the amount of bandwidth available as downstream link. Audio
resources are also enumerated as part of this procedure. This is to
determine the number of end points that are available for streaming
in any given point in time.
[0030] Link bandwidth enumeration feeds into operating system
operations, such as video mode enumeration. Based on this and
asynchronous selection by the end user of the video mode to be
driven out, a commit procedure may be accomplished using a
COMMIT_PATH_RESOURCES message 24 as follows. Enumerated bandwidth
may not be available at commit time. For example, different sources
may send different ENUM_PATH_RESOURCES messages at any given time
to the same sink. They could also be for different sinks with paths
that have a common link. As an example, the sequence of source
number 1 enumeration, followed by source number 2 enumeration,
followed by source number 1 commit, is followed, for example, by
source number 2 commit which fails because of the previous source
number 1 commit.
[0031] The source 10 sends a COMMIT_PATH_RESOURCE message 24 to the
sink 16. The message has the desired bandwidth and number of
streams. All devices along the specified path (e.g. branches 12 and
14) reserve the resources for this source. The replies 26 and 28
may indicate a success or failure.
[0032] Each device propagates COMMIT_PATH_RESOURCES 24 only when it
is able to successfully commit the desired resources. In addition
to independent resource commits from different source devices, it
is possible that the intermediate links along the path may retrain
to a lower bandwidth, providing another reason for failure. Link
training is the handshake that is performed to make the transmitter
or receiver agree on an electrical configuration. To account for a
topology of devices, this notion is extended to an entire path,
where each link on the path needs to be trained in a coordinated
fashion called path training.
[0033] It is possible that some devices may have successfully
committed resources for a video stream before a downstream device
fails to commit. In order to release these resources, the source
device may send out a RELEASE_PATH_RESOURCES 30 message after
receiving a failure on COMMIT_PATH_RESOURCES.
[0034] An active video starts after successful completion of
COMMIT_PATH_RESOURCES. Conversely, when the stream is to be
terminated, the source issues RELEASE_PATH_RESOURCES 32 to enable
release of committed resources at devices along the path.
[0035] Referring to FIG. 3, the source 10, sink 16, and each of the
branch devices 12 or 14, indicated in FIG. 3 as 34, includes a
processor 36. The processor may be coupled to a receiver 38 and the
transmitter 40. The processor 36 may also be coupled to a storage
42 which stores software including the enumerate software 44, in
one embodiment. Thus, the storage 42 may a computer readable medium
that stores instructions executed by the processor 36. The storage
42 may be a semiconductor, optical, or magnetic memory.
[0036] The enumerate sequence 44, shown in FIG. 4, may be software
in one embodiment, but it also may be implemented in hardware or
firmware. A check at diamond 46 determines whether an enumerate
message has been received by a branch device. If so, the message
receiving branch device replies to the upstream branch device with
the receiving device's available bandwidth and available number of
streams.
[0037] If a receiving device does not receive the enumerate message
after a period of time, a check at diamond 50 determines if a
non-receiving device is an upstream device that receives a message
from a downstream device specifying a bandwidth and number of
streams. If so, the upstream device modifies the received bandwidth
and number of streams needed to reflect its capabilities. It then
sends either the original bandwidth and number of streams or the
modified numbers, as needed, to the next branch or to the source,
as indicated in block 54.
[0038] Referring to FIG. 5, a message sequence chart for addition
and deletion of a stream includes a source 60 and two sinks 62, 64
with appropriate stream identifiers. The identifier for sink1 62 is
"1" and the identifier for sink2 64 is 1.2. Each device includes a
port labeled "1" or "2".
[0039] Then, referring to FIG. 6, a sequence chart between a
source1 60, a branch plus sink1 62, and a sink2 64 is depicted. AUX
refers to the control channel and main link refers to the data
channel.
[0040] Each link in a topology, such as that shown in FIG. 5, for
example, may consist of independent control and data channels and
the connections are point-to-point. There is an ability to send
messages on the control channel to any device using addressing and
routing mechanisms. The procedure involves locally unique
identifiers for the stream at the sources and maintenance of
mapping tables and concentrators, as shown in FIG. 6.
[0041] During an address generation phase, addresses are agreed to
for each of the devices in the topology by sending address
generation messages 66. Then the source sends ENUM_PATH_RESOURCES
message 68 to the branch+sink1 62 over the control channel,
indicated as AUX. It also sends a COMMIT_PATH_RESOURCES message 70
over the control path as well as to the branch+sink1 62.
[0042] Binding is the procedure by which devices in the topology
agree on a destination for the next stream. The binding procedure
begins, after enumeration, with a source wanting to transmit a new
stream, sending out an ADD_STREAM message 72 to the desired
destination sink device identified with a locally unique stream
identifier (e.g. 1.2 for sink2). All devices along the path from
source 60 to sink device 64 remember the stream identifier and the
input port (e.g. 1 or 2) on which the stream has been received in
their mapping tables.
[0043] Each branch device 62 performs a mapping of the input stream
identifier (ID 1 for itself) to an output stream identifier (1.2
for sink2 64). In the absence of multiple sources, the input stream
identifier is the same as the output stream identifier. Each
branching device remembers the output stream identifier and output
port number in its mapping table as well.
[0044] Finally, the branch devices forward the message onwards to
the destination as indicated by the route/address contained in the
message, assuming there are no other resource constraints on those
devices, as indicated at 74. In case of such resource constraints,
the branch device simply sends a negative acknowledgement to the
source. The message ends at the desired destination. If the sink
device is able to receive the stream, it responds with an
acknowledgement 76 to the source. Otherwise, the sink device sends
a negative acknowledgement. Then the sink knows that it needs to
consume the next new stream that is on the data channel. All branch
devices propagate the acknowledgements 78 back up to the
source.
[0045] Upon receipt of the acknowledgement, the source device sends
the new stream 80 out on the data channel on its link that leads to
the desired destination. The branch device routes the stream along
the path for the new stream as remembered from their mapping
tables, as indicated at 82. The sink device knows it needs to
consume the new stream based on the message it had previously
received and presents the stream on the display.
[0046] Unbinding or deletion is performed through the delete stream
message 84, 86 sent to the intended destination with the same
stream identifier. This causes the sink device to expect stoppage
of the stream and for the branch devices to alter their mapping
tables accordingly. Receipt of an acknowledge message to a delete
stream message triggers the source to stop sending the stream on
the data channel.
[0047] In FIG. 7, various display configurations can be established
for the topology shown in FIG. 4. A "single display" configuration
is simply one display device that presents audio video data. It
uses the messages 72, 74, 80, 82, 84, and 86 already described. The
"clone mode" configuration is where the same content 92 is sent to
be displayed on two monitors or display devices. "Extended desktop"
is an alternative dual display configuration in which different
images 94, 96 are shown on both monitors.
[0048] When multiple sources are present in the topology, as
indicated in FIG. 8, from source1 98 and source2 100, each source
may issue an ADD_STREAM message with the same stream identifier (in
this case #1) at the same time on an overlapping path. In this
case, a concentrator branch device 102 that is on the overlapping
path for these new streams only propagates an ADD_STREAM message
for one source (in this case source1), while blocking the others.
That is, only one new stream can be added at a time. After the
unblocked source's message has been conveyed on the data channel,
an additional ADD_STREAM message is propagated for the blocked
source.
[0049] In the presence of multiple input ports on a branch device
104, the next available stream identifier is assigned and the
branch device remembers the input stream identifier and port number
to its output stream identifier and port number in its mapping
table 108.
[0050] As one use case, a new stream may be added. The concentrator
branch device adds a new entry to its mapping table when it sees an
add stream message with an identifier that is not active. If
needed, it generates a new output identifier for that stream and
uses that while propagating the ADD_STREAM message. A concentrator
branch device may add a destination address for this identifier in
its mapping table. Another use case is an existing stream extended.
If the same source adds a second sink to a stream that is already
active through another ADD_STREAM message, the concentrator branch
device will not add a new entry in its mapping table since the
mapping it had already created is still valid. However, the
concentrator does add the second destination address to its input
identifier in its mapping table.
[0051] Still another use case is the removal of a sink from a
stream. The concentrator marks the address of the sink for deletion
from a list of destination devices when it receives a delete stream
message with that sink's address for an active identifier.
Subsequently, when it receives a delete stream acknowledgement
message from the sink device, it propagates the message back to the
source using the mapping table to alter the identifier that will be
recognized by the source. It then deletes the sink's address for
that stream from its mapping table. If that was the last sink
receiving the stream with that identifier, it deletes the entry
from its mapping table. Otherwise, if there is at least one other
sink consuming the stream with that identifier, the entry in the
mapping table is not deleted.
[0052] Referring to FIG. 9, a sequence 110, in accordance with one
embodiment for implementing the binding described above, is
depicted. The sequence may be implemented in software, hardware, or
firmware. In software embodiments, the sequence may be implemented
by instructions executed by a processor, such as the processor 36
shown in FIG. 3, for a branch device 34. In such case, the sequence
may be stored on the storage 42.
[0053] Initially, a branch device receives an ADD_STREAM message,
as indicated in block 112. It stores the STREAM_ID and the input
port from that message in its mapping table, as indicated in block
114. Then the branch device maps the input STREAM_ID to an output
STREAM_ID, as indicated at block 116. It stores the output
STREAM_ID and output port number in its mapping table, as indicated
in block 118. Then it forwards the message onwards, as indicated in
block 120. Ultimately, if the message is successfully delivered, an
acknowledgment message will be received from a downstream device
and the branch device forwards the acknowledgement message
upstream, as indicated in block 122.
[0054] In some embodiments, a message passing framework 124, shown
in FIG. 10, may allow for action by all devices along a path or
action only by the destination device. Messages have identifiers,
with a new identifier being allocated as each new message is
defined. The definition of a message includes determination of
whether it is a path or a destination message. Path messages are of
two types, depending on the direction in which the action is
performed, on the way down towards the sink, in which case it is a
down action path message, or on the way back up to the source
device, in which case it is up action path message. Messages may be
initiated by any device in the topology. Each message has a
destination address and associating routing information.
[0055] The message passing framework 124, shown in FIG. 10, may be
implemented in software, hardware, or firmware. For example, it may
be implemented in software in the form of instructions stored on a
computer readable medium, such as the storage 42 shown in FIG. 3,
in the device 34, which may be a branch device or sink device, for
example.
[0056] In accordance with one embodiment, the sequence shown in
FIG. 10 begins by receiving a message from an upstream device, as
indicated in block 126. The device receiving the message may be a
branch device or a sink device, as two examples. The receiving
device, whether it is the ultimate destination or not, obtains the
message definition, as indicated in block 128. Then, in diamond
130, the device checks to determine whether an up action message is
indicated by the message definition. If so, it performs the actions
requested in the message on receipt of the message, as indicated in
block 132.
[0057] Otherwise, it is not an up action message, a check at
diamond 134 determines whether it is a down action message. If it
is a down action message, as indicated in block 136, the actions
are performed on the acknowledgement, as opposed upon the receipt
of the message.
[0058] Conversely, if it is not a down action message, then, as
determined in diamond 138, if it is a destination message, the
action is only performed if the device receiving the message is the
ultimate destination, as indicated in block 140.
[0059] The message passing framework enables devices to perform
coordinated action on a specified path in a point-to-point topology
of connected audio visual source, branch, and sink devices. The
framework can be used for a variety of operations including
topology discovery, address generation, routing, binding and stream
management, resource management, and power management.
[0060] A down action message, shown in FIG. 11, works as follows.
Prior to sending a message, the source 110 performs any message
specific action 119 needed. The message 112 is sent only if the
source action succeeds. The source device transmits a message to
the destination device by sending it on a downstream port, as
determined based on the address/routing information. Each branch
device 114 or 116 or sink 118 that receives the message performs
action 119 as required by that message type. Upon the successful
completion of action at the destination (e.g. sink 118), it
responds with an acknowledgement (ACK) 120. This acknowledgement is
propagated back up to the source.
[0061] An up action message 122 works as depicted in FIG. 12. Here,
the actions 119 are done as part of the acknowledgement 120.
[0062] Destination messages work as depicted in FIG. 13. Action 119
is only done by the destination, in this example, the sink 118. The
other devices in the path simply forward the message and the
acknowledgement.
[0063] A use of a down action path message is illustrated in FIG.
14 for path training, which is training all the links on a path. In
FIG. 13, the action 119 at each device is link training. The
message used is TRAIN_LINKS_ON_PATH, although any other message
could be used. In FIG. 13, the message is directed at branch
116.
[0064] FIG. 15 is a message sequence chart for TRAIN_LINKS_ON_PATH
when implemented as an up action message. Here, the actions 119 all
occur as part of the acknowledgements 120.
[0065] An interface-specific framework may enable a source device
to determine that the functions enumerated through different paths
are part of the same device. The DisplayPort Standard is an example
of an "interface." Different paths for enumeration can be: a) paths
featuring different interface types or b) just different paths
within the same interface type. The framework enables a device to
be used in conjunction with container identifier initiatives that
Microsoft.RTM. Windows.RTM. and other technologies, such as
Universal Serial bus (USB) support, and enables device centric
rather than function centric user interfaces for connected
devices.
[0066] The framework may include a 16 byte globally unique
identifier (GUID) exposed through a set of container_ID registers
(which could be DisplayPort configuration data (DPCD) in the case
of DisplayPort). The DPCD is essentially a set of registers used
for status checking, command communication, and providing context
for an interrupt. The container_ID registers may be supported on
branch devices, composite sink devices, and any device that has
multiple transports.
[0067] A sink device with a given number of video end points is
expected to respond with that number of Extended Display
Identification Data (EDID) structures. The EDID data structure
tells the source about the capabilities of the monitor. EDID is a
VESA standard. When a sink device has an integrated Universal
Serial Bus (USE) or hub device, the globally unique identifier of
the sink matches the globally unique identifier in the container
descriptor of that USE device or hub. All functions that are
integrated into the device advertise the same globally unique
identifier, regardless of the interface type through which they are
accessed. In a sink that has multiple video end points, the
container_ID registers from each address returns the same globally
unique identifier. For each device in the topology, the source
device reads the globally unique identifier as part of the topology
discovery process. If the device contains a globally unique
identifier, the source device reads the globally unique identifier
to determine if the same device has been accessed for multiple
paths or through multiple interfaces.
[0068] Otherwise, a source device infers the functions that are in
the same physical device through some interface specific means. In
the case where the interface is a DisplayPort Standard, this can be
based on the relative address (RAD) of the downstream device. When
faced with a topology of devices, each device initiating
communication needs to generate an address for the destination
device that is valid in the network. That address is called the
relative address because the address generated by each device is
valid but could be different from what is generated on another
source for the same destination. Then, the source reads the EDID
from each relative address. A globally unique identifier is
generated and associated with the device as identified through
EDID. This generated globally unique identifier is used with the
container identifier framework in the operating system.
[0069] Thus, the EDID contains a unique serial number in some
embodiments. If this is not valid, there is a change of the same
globally unique identifier being associated with multiple EDIDs,
resulting in poor user experience.
[0070] Multiple connections between source and branch devices are
shown in FIG. 16. In this case, the source generates two addresses
for the sink device since there are two paths to that sink. Since
the source reads the same globally unique identifier through both
paths, it is able to infer that both paths read the same sink
device. Had the globally unique identifier been missing, the source
reads the EDID from both paths which would be the same, generates a
globally unique identifier, and associates that globally unique
identifier with the sink device. This identifier is then returned
to the operating system.
[0071] FIG. 17 shows an example with two video end points. The
sequence of the source is as follows. The source again generates
two addresses, one for each video end point in the sink device. The
source reads the container identifier for the register from each
video end point address. Since the sink has two interfaces into it,
the framework requires a globally unique identifier to be present
in the sink and requires that globally unique identifier to be the
same in both interfaces. The source detects that the globally
unique identifier is the same and infers that the two video end
points are part of the same physical device.
[0072] Referring to FIG. 18, in accordance with one embodiment, a
sequence 150 may be implemented by a source in the form shown in
FIG. 3. In some embodiments, the sequence shown in FIG. 18 may be
implemented in software, hardware, or firmware. In software
embodiments, it may be implemented by a sequence of instructions
executed by a processor, such as the processor 36, and stored on a
storage device 42.
[0073] During an initial enumeration or topology discovery phase,
an identifier is read for each device in the topology (block 152).
In other words, the source obtains the identifier for the devices
in the topology. That identifier can be any of the identifiers
already discussed herein. Then the source establishes a connection
to a destination downstream of the source via a path, as indicated
at block 154. Then the source compares the identifiers of the
device in the connection path, as indicated in block 156. If, as
determined in block 158, the identifiers match, the source
concludes that the path devices with matching identifiers are part
of the same branch or sink device. Thus, the ambiguity that may
arise when two devices have the same identifier may be handled
easily, in some embodiments.
[0074] References throughout this specification to "one embodiment"
or "an embodiment" mean that a particular feature, structure, or
characteristic described in connection with the embodiment is
included in at least one implementation encompassed within the
present invention. Thus, appearances of the phrase "one embodiment"
or "in an embodiment" are not necessarily referring to the same
embodiment. Furthermore, the particular features, structures, or
characteristics may be instituted in other suitable forms other
than the particular embodiment illustrated and all such forms may
be encompassed within the claims of the present application.
[0075] While the present invention has been described with respect
to a limited number of embodiments, those skilled in the art will
appreciate numerous modifications and variations therefrom. It is
intended that the appended claims cover all such modifications and
variations as fall within the true spirit and scope of this present
invention.
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