Patent Publication Number: US-2021181832-A1

Title: Display link power management using in-band low-frequency periodic signaling

Description:
TECHNICAL FIELD 
     This disclosure relates in general to the field of computer systems and, more particularly, to power management for display links (e.g., DisplayPort-based links) using low-frequency periodic signaling (LFPS). 
     BACKGROUND 
     DisplayPort specifications currently do not have link power management mechanisms; however, embedded DisplayPort (eDP) specifications define a mechanism for Advanced Link Power Management (ALPM). The current eDP link management technique involves the use of wake signaling over a sideband AUX (auxiliary) interface. This technique may have one or more issues when applied to DisplayPort embodiments, however. For instance, it may require a tight coupling between the main link and the AUX interface that is unmanageable over the display topology (which may include a number of different devices, e.g., docks, branch devices, LTTPRs, etc.). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of an example computing system in accordance with certain embodiments. 
         FIG. 2  illustrates an example sleep signaling sequence in a DisplayPort-based topology in accordance with certain embodiments. 
         FIG. 3  illustrates an example Low Frequency Periodic Signaling (LFPS)-based sequence in accordance with certain embodiments. 
         FIG. 4  illustrates an example LFPS-based wake sequence in accordance with certain embodiments. 
         FIGS. 5A-5B  illustrate an example LFPS-based wake sequence in a DisplayPort-based topology in accordance with certain embodiments. 
         FIG. 6  illustrates another example LFPS-based wake sequence in a DisplayPort-based topology in accordance with certain embodiments. 
         FIG. 7  is a flow diagram of an example process of initiating a transition from an active link state to a low power link state in accordance with certain embodiments. 
         FIG. 8  is a flow diagram of an example process of initiating a transition from a low power link state to an active link state in accordance with certain embodiments. 
         FIG. 9  is an example illustration of a processor according to an embodiment. 
         FIG. 10  illustrates a computing system that is arranged in a point-to-point (PtP) configuration according to an embodiment. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     In the following description, numerous specific details are set forth, such as examples of specific configurations, structures, architectural details, etc. in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that these specific details need not be employed to practice embodiments of the present disclosure. In some instances, well known components or methods may be utilized, and such details haven&#39;t been described in detail in order to avoid unnecessarily obscuring embodiments of the present disclosure. 
       FIG. 1  illustrates a block diagram of an example computing system  100  in accordance with certain embodiments. The example computing system  100  comprises a display  102  coupled to a video source device  104  (also referred to herein as a “display source” or “source”) via a link  106 . In the example shown, the display  102  is coupled to a video source device  104  to display a representation of a video signal received from the video source device  104 . The display  102  comprises a scaler chip  108 , a display driver  110 , a panel  114 , and a memory  116 . Some embodiments may include a display with any suitable combination of components (including any of those shown or other components). Scaler chip  108  includes standby controller  118 , port input selector  120 , image processor  122 , timing controller (TCON) interface  124 , backlight controller  126 , central processing unit (CPU)  128 , and memory controller  130 . 
     Standby controller  118  is operable to manage operations associated with entry into standby and exit from standby for the display  102 . For example, the standby controller  118  may coordinate a context save and restore procedure, or the entry into and exit from standby for the display  102 . In various embodiments, standby controller  118  may coordinate with other components of display  102 . In some embodiments, all or a portion of standby controller  118  may be integrated within another component of the scaler chip  108 , such as the port input selector  120  or CPU  128 ; or other component of the display  102 . Thus, in some embodiments the standby controller  118  may be a distinct logic component or may include a collection of logic from various components of the scaler chip  108  (or other components of the display  102 ). 
     Port input selector  120  is operable to select a port from among a plurality of ports of the display  102  and to pass a video signal received through the port to a processing pipeline of the display  102 . The port input selector  120  may include a port interface that comprises or is coupled to a plurality of ports of the display. The display  102  may include any number of ports of any type. For example, display  102  may include a DisplayPort™ port, a High-Definition Multimedia Interface (HDMI™) port, a Universal Serial Bus (USB) port, a Digital Visual Interface (DVI) port, a Video Graphics Array (VGA) port, or other suitable port. Display  102  may include any suitable combination of ports, including multiple ports of the same type or multiple ports of different types. The port input selector  120  may include selection logic coupled to the port interface to select a particular port and to pass the signal received through the particular port on to additional logic (e.g., the standby controller  118 , the image processor  122 , etc.). In some embodiments, the port input selector  120  may also include conversion logic to receive a signal from any of the ports of the display  102  and convert the signal to a common format (e.g., a digital pixel format) for further processing. 
     Image processor  122  may receive a video signal from the port input selector  120  and perform further processing on the video signal. In some embodiments, the image processor  122  may execute one or more algorithms to improve the image quality of the video signal. For example, image processor  122  may perform resolution upscaling, contrast adjustment, color adjustment, or other suitable image processing. In some embodiments, image processor  122  may superimpose one or more images (e.g., a user menu of the display  102 ) on the video signal. 
     TCON interface  124  may receive a processed signal from image processor  122  and convert the signal to a format (e.g., a serial high speed interface format such as Embedded DisplayPort™ (eDP) or V-by-One®) compatible with a TCON of the display driver  110 . 
     Backlight controller  126  may include a backlight driver and may generate signals that may be used by the backlight driver to produce current to light up the panel  114 . 
     CPU  128  may provide various functions of the display  102 . For example, the CPU  128  may manage the on-screen display and user configuration adjustments of the display  102 . The CPU  128  may communicate with other components of the display  102  (e.g., to bring up a menu or change the brightness of the display in response to a user selection). 
     Memory controller  130  may control the transfer of data between one or more components of the scaler chip  108  and the memory  116 . Memory  116  may include any suitable volatile or non-volatile memory to support the operations of the display  102 . For example, the memory  116  may be used to store instructions executed by the components (e.g., CPU  128 , standby controller  118 , image processor  122 , or other component), frame data (e.g., values of pixels), on-screen display data, or other suitable data. In some embodiments, memory  116  may comprise multiple different memory modules (e.g., each of which may be dedicated to particular types of data) located on any one or more components of the display  102 . For example, in various embodiments, the scaler chip  108  may include one or more memory modules to support the operation of the scaler chip  108 . 
     Display driver  110  may comprise circuitry to receive a video signal and to drive electrical signals to the display elements of the panel  114  to cause the panel  114  to display the video. In a particular embodiment, display driver may comprise a TCON. In a particular embodiment, display driver  110  comprises one or more row and column drivers to drive the display elements. The display driver  110  may include one or more digital to analog converters (DACs) to produce the appropriate currents to drive the display elements. 
     In various embodiments, panel  114  may generate light or allow for the transmission of light in a plurality of pixels. Panel  114  may comprise a display substrate on which a plurality of pixels are located. The pixels define a display area within which a video signal comprising still images, videos, or other content defined by a video signal can be displayed. Panel  114  may utilize any suitable display technology, such as, e.g., a thin-film-transistor liquid crystal display (TFT LCD), micro-light emitting diode (micro-LED), organic LED (OLED), quantum dot LED (QLED), or other suitable display technology. 
     The components of the display  102  may be arranged in any suitable manner. In one embodiment, a first printed circuit board may comprise the scaler chip  108  and a second printed circuit board may comprise the display driver  110  (in some embodiments a separate printed circuit board may house the TCON). In some embodiments, memory  116  or a portion thereof may be included on the first printed circuit board (or integrated on the scaler chip  108 ). 
     Video source device  104  may be any suitable computing device to communicate a video signal to the display  102 . For example, video source device  104  may be a desktop computing system, a laptop computing system, a server computing system, a storage system, a handheld device, a tablet, or other suitable computing device. 
     In the embodiment depicted, video source device  104  comprises processor  132 , operating system  136  (which may be executed by processor  132 ), memory  140 , I/O controller  142 , and graphics processing unit (GPU)  144 . Processor  132  is depicted as including two processing cores  134 A and  134 B, though the processor  132  may include any suitable number of cores. 
     The operating system  136  may execute a display driver  138  that controls the connection from the video source device  104  over the link  106  to the display  102  and the communication of the video signal (and supporting communications) over the connection. 
     The GPU  144  may generate the video signal that is communicated to the display  102 . In the embodiment depicted, the GPU  144  is a discrete component, though in other embodiments, the GPU  144  may be integrated with processor  132 . 
     Memory  140  may include any suitable volatile or non-volatile memory to support the operations of the display  102 . The memory  140  may be used to store instructions executed by the components (e.g., processor  132  or GPU  144 ), or other suitable data. In some embodiments, memory  140  may comprise multiple different memory modules (e.g., each of which may be dedicated to particular types of data) located on any one or more components of the display video source device  104 . In some embodiments, memory  140  may comprise a system memory. 
     Link  106  may comprise any suitable transmission medium operable to communicate analog or digital data between the display  102  and the video source device  104 . In some embodiments, link  106  may comprise a cable with a connector on each end. For example, link  106  may comprise a DisplayPort™ cable, an HDMI™ cable, a USB cable, a DVI cable, a VGA cable, or other suitable cable. In some embodiments, the link  106  may be an internal connection between the video source device  104  and the display  102  (e.g., for notebook computers or other computer systems with connected or embedded displays). 
     In some embodiments, the link  106  may implement a specification-based protocol, such as a DisplayPort or Embedded DisplayPort (eDP) protocol. Current eDP specifications define a mechanism for Advanced Link Power Management (ALPM), while current DisplayPort specifications do not have link power management mechanisms. The current eDP link management technique involves the use of wake signaling over a sideband AUX (auxiliary) interface. This technique may have one or more issues, however, when applied to DisplayPort topologies. For instance, it may require a tight coupling between the main link and the AUX interface that is unmanageable over the display topology (which may include a number of different devices, e.g., docks, branch devices, LTTPRs (Link-Training Tunable PHY Repeaters), etc.). There is no current solution in DisplayPort specifications for link state power management over the display topology—i.e., once the display is on, the link must stay up and in an active state. 
     Embodiments of the present disclosure may provide a unified link-based mechanism for entry and exit from power managed link states in both DP and eDP topologies. In certain instances, embodiments of the present disclosure may be comparable in power to the current eDP mechanism, but may be able to be deployed for both eDP and DP topologies. In particular embodiments, for instance, a Low Frequency Periodic Signaling (LFPS) may be utilized over a main link. The LFPS does not require a handshake over the AUX interface and can therefore be applied to a DisplayPort topology. In addition, it provides a low latency and low power mechanism that can be used for eDP as well, allowing for a unified approach for link state power management for both eDP and DP topologies. 
       FIG. 2  illustrates an example sleep signaling sequence  200  in a DisplayPort-based topology in accordance with certain embodiments. In particular, the examples show a sleep signal pattern  202  that is transmitted from a DisplayPort-compatible or eDP-compatible transmitter (DPTX)  210  (e.g., video source device  104  of  FIG. 1 ) to a DisplayPort-compatible or eDP-compatible receiver (DPRX)  230  (e.g., display  102  of  FIG. 1 ) via a number of intermediate LTTPRs  221 - 228 . As per certain DisplayPort specifications (e.g., DP v2.0), a source device (e.g., source device  104  of  FIG. 1 ) may be required in certain instances to indicate to a sink device (e.g., display  102  of  FIG. 1 ) through an AUX-based DPCD (DisplayPort Configuration Data) register write operation indicating that it is turning off the main link. This can add hundreds of micro-seconds of latency, which makes this scheme unusable for quick turnoff/on between active frames. However, in embodiments of the present disclosure, source device may transmit a specific pattern or packet (e.g., as described below) on the main link that indicates the main link is transitioning to a lower power state. The source, intermediate branch/retimer (e.g., LTTPR), and sink devices may accordingly transition into low power states locally after the indication is received. 
     As shown in  FIG. 2 , each device in the topology may decode the advanced link power management pattern/code sequence (e.g., pattern  202 , which may be a ML_PHY_SLEEP as described below), or packet and react accordingly. As there are multiple devices in the example display topology shown in  FIG. 2 , the DPTX  210  and LTTPRs ( 222 - 228 ) may continue to transmit the link power management patterns on the main link as shown until all the devices in the topology have decoded the pattern and taken appropriate action. 
     For instance, the DPTX  210  may transmit a ML_PHY_SLEEP/_STANDBY pattern (e.g., as described below) a number of times equal to the number of devices on the link other than the source device (e.g., number of intermediate devices+display), which may be equal to one more than the number of LTTPRs in the topology (TOTAL_LTTPR_CNT+1). In the example shown, that means the DPTX  210  transmits the pattern 9 times. The DPTX may transmit each sleep pattern in 80 bits for 8b/10b encoding or 129 bits for 128b/132b encoding, and may transmit a minimum of 2560 bits (for 8b/10b) or 4096 bits (for 128b/132b) of scrambled zeroes  204  between the patterns  202  as shown in  FIG. 2 , after which it may provide an output at the common mode voltage (indicated by OFF in  FIG. 2 ). The DPRX  230 , after receiving a ML_PHY_SLEEP/STANDBY pattern  202  may turn off its high-speed receiving circuit until it senses an Low Frequency Periodic Signaling (LFPS) wake signal as described below. Intermediate LTTPRs may count the number of ML_PHY_SLEEP/_STANDBY patterns it receives/detects on its UFP, and once the number of patterns detected becomes equal to its LTTPR_CNT+1, it may provide an output at the common mode voltage on its DFP TX_PHY. For example, LTTPR8  228  in  FIG. 2  (LTTPR_CNT=8) may provide the common mode voltage after detecting  9  ML_PHY_SLEEP/STANDBY patterns on the UFP  228   u . The maximum latency on the ML_PHY_SLEEP transmission through the LTTPR may be no more than 2560 bits (for 8b/10b) or 4096 bits (for 128b/132b) bit-time. 
     In certain instances, the pattern used for reduced bit rate (RBR) and high bit rate (HBR) frequencies could be the same patterns used in the eDP standard for link management, as shown in Table 1 below. In the case of ANSI8b10b encoding, the transmitter may maintain disparity across the sequence. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Link Management signaling scheme for ANSI8b10b encoding 
               
            
           
           
               
               
               
            
               
                   
                 PHY Layer Power- 
                 Advanced Link Power 
               
               
                 Coding 
                 Down Signal 
                 Management Code Sequence 
               
               
                   
               
               
                 8b_10b 
                 ML_PHY_SLEEP 
                 K28.5, K27.7, K28.5, K27.7, 
               
               
                   
                   
                 K28.5, K28.5, K28.5, K28.5 
               
               
                   
                 ML_PHY_STANDBY 
                 K28.5, K27.7, K28.5, K27.7, 
               
               
                   
                   
                 K27.7, K27.7, K27.7, K27.7 
               
               
                   
               
            
           
         
       
     
     An example of an advanced main link power management packet for UHBR* frequencies with 128b_132b encoding are shown in Table 2 below. The 1-bit CDI may be set to 1 and XORing 12 of the 1-bit CDIs with 333h for DC balancing may continue as in normal operation. The sequence shown in Table 2 is without pre-coding—during transmission pre-coding would be applied to the sequence, hence DC balancing may be maintained. The pattern may be transmitted starting at any 129-bit Word boundary. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Link Management signaling scheme for 128_132b encoding 
               
            
           
           
               
               
               
            
               
                   
                 PHY Layer Power- 
                 Advanced Link Power 
               
               
                 Coding 
                 Down Signal 
                 Management Packet 
               
               
                   
               
               
                 128b_132b 
                 ML_PHY_SLEEP 
                 CDI + 89898989, 89898989, 
               
               
                   
                   
                 89898989, 89898989 
               
               
                   
                 ML_PHY_STANDBY 
                 CDI + 89555555, 89555555, 
               
               
                   
                   
                 89555555, 89555555 
               
               
                   
               
            
           
         
       
     
       FIG. 3  illustrates an example Low Frequency Periodic Signaling (LFPS)-based sequence  300  in accordance with certain embodiments. The example LFPS sequence  300  may be transmitted by a display source (e.g., video source device  104  of  FIG. 1 ) over a link (e.g., link  106 ) to a display (e.g., display  102  of  FIG. 1 ) to wake the display from a sleep or standby state. In certain embodiments, the LFPS sequence  300  may be implemented in a DisplayPort or Embedded DisplayPort (eDP)-based topology. 
     In certain embodiments, two low-power link states may be defined, e.g., a “ML_PHY_SLEEP” sleep state and “ML_PHY_StandBy” standby state. These link states may address a wake scenario for Decision Feedback (DFE) refresh at HBR3 (High Bit Rate 3) and UHBR (Ultra High Bit Rate). In some instances, the standby state may be implemented, e.g., when the main link off time is below 40 uSec, and the sleep state may be implemented when the main link off time is 40 uSec and above. Aspects of the example LFPS sequence  300  or another type of LFPS signal may be sent over the main link to exit from either of these power management link states. 
     The example LFPS sequence  300  includes segments  310 ,  320 ,  330 ,  340 . The segment  310  indicates a common mode, e.g., the standby or sleep mode as described above. The segment  320  includes a set of low-frequency pulses that are used to indicate a transition out of the sleep or standby state. In certain embodiments, the segment  320  includes at least 7 fixed length pulses with a pulse length (tPeriod) between 25 ns-50 ns, amounting to a total segment time between 175 ns-400 ns. The segment  330  is a silent period in which no signals are transmitted. In certain embodiments, the period of silence may be defined as the lanes in Common Mode, and the silence period may be between 80 nS-120 nS before a signal is transmitted in the segment  340 . The signal transmitted in the segment  340  may be a PHY link (physical link) establishment signal. For instance, in the example shown, the segment  340  includes a ML_PHY_LOCK or ML_PHY_LOCK_LTTPR pattern transmission. The ML_PHY_LOCK/ML_PHY_LOCK_LTTPR pattern transmission may be used for calibration, equalization, and/or activation by a display or LTTPR in certain instances. 
     In certain embodiments that implement reduced bit rate (RBR) or ultra high bit rate (UHBR) frequencies that use ANSI8b10b coding, the ML_PHY_LOCK pattern may include TPS4 (CP2520 Pattern 3)−K28.0−, K28.5−, K28.5+, K28.0−, 248 00 hs, and the ML_PHY_LOCK_LTTPR may include the CP2520 Pattern 1 with count indication of 248: −K28.0−, K28.1+, K28.1+, K28.0−248 00 hs. In certain embodiments that implement UHBR* frequencies that use 128b/132b encoding, the ML_PHY_LOCK pattern is the same as 128b/132b_tps2 with one change where the LT_SCRAMBLER_RESET PHY sync replaces replaced every 4th PHY_SYNC_ONLY PHY sync symbol, as opposed to every 16th on the 128b/132b_tps2. This pattern may reduce wake latency in certain instances. The ML_PHY_LOCK_LTTPR pattern for 128b/132b_tps2_wake_LTTPR may be the same as the 128b/132b_tps2_wake pattern but with new coding for PHY_SYN_ONLY symbol 3355AA55h, replacing 333C3C3Ch. 
     In some embodiments, devices in the topology may repeat the transmission of the LFPS downstream to other devices of the topology after detecting the pulse sequence of segment  320 . For example, an upward facing port (UFP) in a branch device (e.g., LTTPR_UFP) may transmit or repeat the LFPS to the next downstream device once a threshold number of pulses (e.g., 3) are detected. Table 3 below indicates example LFPS Parameters that may be implemented. In some eDP topology embodiments, the LPFS may use lower clock frequencies (e.g., 1 MHz) to reduce power with increased latency. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 LFPS Parameters 
               
            
           
           
               
               
               
               
               
            
               
                 Symbol 
                 Description 
                 Min 
                 Max 
                 Units 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 tPeriod 
                 Period of LFPS 
                 25 
                 50 
                 ns 
               
               
                   
                 cycle (clock 
               
               
                   
                 pattern) - 
               
               
                   
                 enables clock 
               
               
                   
                 frequences 
               
               
                   
                 between 
               
               
                   
                 20-40 MHz 
               
               
                 LFPS Period 
                 Duration for 
                 175 
                 400 
                 ns 
               
               
                   
                 LFPS Sequence 
               
               
                   
                 7-10 pulses of 
               
               
                   
                 tLFPS_Cycle 
               
               
                 tSilence 
                 Period of time 
                 80 
                 120 
                 ns 
               
               
                   
                 for which slience 
               
               
                   
                 shall be set after 
               
               
                   
                 the LFPS 
               
               
                   
                 sequence 
               
               
                 V_CM_AC_LFPS 
                 Common mode 
                 — 
                 100 
                 mV 
               
               
                   
                 noise 
                   
                   
                 pk-pk 
               
               
                 V_TX_DIFF_PP_LFPS 
                 LFPS 
                 800 
                 1200 
                 mV 
               
               
                   
                 peak-to-peak 
                   
                   
                 pk-pk 
               
               
                   
                 differential 
               
               
                   
                 amplitude 
               
               
                 V_LFPS_RX_DETECT_TH 
                 LFPS RX detect 
                 100 
                 300 
                 mV 
               
               
                   
                 threshold -- 
                   
                   
                 pk-pk 
               
               
                   
                 Signal shall be 
               
               
                   
                 rejected below 
               
               
                   
                 minimum level 
               
               
                   
                 and shall be 
               
               
                   
                 accepted above 
               
               
                   
                 maximum level 
               
               
                 tRiseFall 
                 Rise/Fall time of 
                 — 
                 4 
                 ns 
               
               
                   
                 LFPS signal, 
               
               
                   
                 measured from 
               
               
                   
                 20% to 80% of 
               
               
                   
                 the signal 
               
               
                   
                 dynamic 
               
               
                 LFPS_DUTY_CYCLE 
                 Duty cycle of the 
                 45 
                 55 
                 % 
               
               
                   
                 LFPS signal - 
               
               
                   
                 applies for all 
               
               
                   
                 LFPS cycles 
               
               
                   
               
            
           
         
       
     
       FIG. 4  illustrates an example LFPS-based wake sequence  400  in accordance with certain embodiments. The example wake sequence  400  may be transmitted by a display source (e.g., video source device  104  of  FIG. 1 ) over a link (e.g., link  106 ) to a display (e.g., display  102  of  FIG. 1 ) to wake the display from a sleep or standby state. In certain embodiments, the wake sequence  400  may be implemented in a DisplayPort or Embedded DisplayPort (eDP)-based topology. In the example shown, the wake sequence  400  includes three segments  410 ,  420 ,  430 , followed by a transmission of data on the link. 
     The first segment  410  includes a pulse sequence similar to segment  320  of  FIG. 3 . In the example shown, the pulse sequence of segment  320  includes seven pulses in a period of 166 ns-350 ns. However, any suitable number of pulses and timing may be implemented in other embodiments. In certain embodiments, the pulse sequence may be repeated sequentially over each hop of a topology starting at the display source and ending with the last hop terminating in the display. In certain embodiments, the sequential wake sequence may takes about 175-350 usec period per hop. 
     The second segment  420  includes a physical link (PHY) establishment signaling sequence, which may include link training information for the devices of the link between the display source and display. In the example shown, the second segment  420  begins with a period of silence (e.g., 80-120 ns) followed by a ML_PHY_LOCK/ML_PHY_LOCK_LTTPR sequence for a period t 1  (e.g., 25 uSec for exit from Standby and 50 uSec for exit from sleep to enable DFE calibration). The silence period and period t 1  may be of any suitable length of time, e.g., as shown below in Table 2. In certain instances, the display source (or LTTPR UFP) may have completed CDR_DONE and EQ adjustment based on the pattern (ML_LOCK_PHY for the UFP of the most upstream LTTPR and for ML_LOCK_PHY_LTTPR for the rest of the UFP&#39;s) by the end of the PHY Establishment period t 1 . In certain embodiments, the PHY establishment sequence may be repeated sequentially on all the hops of the topology to reduce latency. For example, each LTTPR in the topology may transmit a locally generated ML_PHY_LOCK_LTTPR pattern on its downward facing port (DFP). 
     The third segment  430  includes a sequential clock and data switch (CDS) sequence, which may be used to establish a clock signal (e.g., from the GPU) in the topology and may be when the symbol and lane alignment occur. The CDS period t 2  may be link-rate dependent, in certain instances. Aspects of the CDS sequence are described further below. 
     These three phases may initiate completion of the exit from the low power states in the link devices to an active power state, and thereafter normal data transmission (video stream) may begin as shown. 
     Table 4 below indicates example wake sequence latencies for DisplayPort UHBR10 implementations. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Example Wake Sequence latencies for UHBR10 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Total Wake 
                 Total Wake 
                   
               
               
                   
                 Time name 
                   
                 Max 
                 Standby 
                 Sleep 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 LFPS 
                 350 
                 ns 
                 350 
                 ns 
                 350 
                 ns 
               
               
                   
                 Silence 
                 120 
                 ns 
                 470 
                 ns 
                 470 
                 ns 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 t1 Standby 
                 25 
                 uSec 
                 25.47 
                 uSec 
                 N/A 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 t1 Sleep 
                 50 
                 uSec 
                 N/A 
                 50.47 
                 uSec 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 t2 
                 11.7 
                 uSec 
                 37.17 
                 uSec 
                 62.17 
                 uSec 
               
               
                   
                   
               
            
           
         
       
     
       FIGS. 5A-5B  illustrate an example LFPS-based wake sequence  500  in a DisplayPort-based topology in accordance with certain embodiments. In particular, the examples show an LFPS-based wake sequence that is transmitted from a DisplayPort-compatible or eDP-compatible transmitter (DPTX)  510  (e.g., video source device  104  of  FIG. 1 ) to a DisplayPort-compatible or eDP-compatible receiver (DPRX)  530  (e.g., display  102  of  FIG. 1 ) via a number of intermediate LTTPRs  521 - 528 , which repeat aspects of the LFPS-based sequence as shown. The LTTPRs may be implemented at various points in the link between the DPTX and DPRX (e.g., link  106  of  FIG. 1 ), such as, for example, in a dock, USB hub, or other intermediate device between the DPTX and DPRX. The same or similar LFPS-based sequence shown in  FIG. 5A  may be implemented in other topologies as well. 
     In the example shown in  FIG. 5A , the DPTX initiates a wake pulse sequence similar to the sequences of segment  310  of  FIG. 3  and segment  220  of  FIG. 2 , which is transmitted to/received by the UFP of LTTPR8  428   u . The wake pulse sequence is followed by a period of silence, a PHY establishment sequence, and a CDS sequence as described above. The LTTPR8 transmits the wake pulse sequence downstream in the topology via the DFP  428   d  (after a small 1.5 us delay). This process is repeated downstream through the other LTTPRs as shown in  FIGS. 5A-5B  ( FIG. 5B  illustrates another view of how each of the signals of the LFPS-based wake sequence are transmitted downstream over time). 
     In some embodiments, an LTTPR may switch from the ML_PHY_LOCK_LTTPR pattern to the ML_PHY_LOCK pattern when it completes the concurrent PHY establishment, with the most upstream LTTPR first and the most downstream LTTPR last. The LTTPR may lock to the incoming clock signal from the GPU during the CDS sequence. Prior to entering the CDS sequence, the PHY EQ may be stable and the symbol boundary/inter-lane may be aligned with incoming ML_PHY_LOCK or ML_PHY_LOCK_LTTPR signals. 
     In some embodiments, the CDS sequence may include the follow operations. First, a LTTPR_UFP may detect the pattern change from the ML_PHY_LOCK_LTTPR to ML_PHY_LOCK pattern, and a loss of lanes/symbol alignment may result due to the clock switch. After three consecutive Training Pattern Sequence (TPS) cycles of the ML_PHY_LOCK pattern, the LTTPR_UFP may realign to the incoming ML_PHY_LOCK. The TPS patterns may be predetermined patterns transmitted on the main link during a link training process. After verifying at least four consecutive TPS cycles, the LTTPR may switch the reference clock of the DFP serial bit clock generation from a local clock to the recovered clock of the UFP, which may take about ˜0.3 uSec in some instances. Thereafter, the LTTPR may switch the DFP transmission pattern from the locally-generated ML_PHY_LOCK_LTTPR to the incoming ML_PHY_LOCK, which may require at least two consecutive TPS cycles of ML_PHY_LOCK before switching to Normal Data in some instances. The total time required may be around 9 TPS cycles+0.3 uSec, in certain instances. The CDS sequence may end with a scramble reset as first symbol for 8b/10b SST or MST and POST_LT_SCRAMBLE_RESET for 128b/132b. 
       FIG. 6  illustrates another example LFPS-based wake sequence  600  in a DisplayPort-based topology in accordance with certain embodiments. In particular, in the example shown, the wake signaling sequence  600  occurs sequentially through the topology (as opposed to the repeating implementation shown in  FIGS. 5A-5B ). For instance, the example wake sequence  600  includes the DPTX  610  (which may be implemented similar to the DPTX  510  of  FIGS. 5A-5B ) initiating a wake pulse sequence similar to the sequences of segment  410  of  FIG. 4  and segment  320  of  FIG. 3 , which is followed by a period of silence, a PHY establishment sequence, and a CDS sequence as described above. However, instead of quickly initiating the wake pulse sequence as described above with respect to  FIGS. 5A-5B  (i.e., only with slight delay of ˜10-15 us), the LTTPR  620  may wait until the CDS sequence is complete before transmitting the wake pulse sequence to the next hop in the topology (e.g., another LTTPR or a DPRX). This sequential transmission pattern may continue until the DPRX is reached, after which the normal data stream may be initiated (as shown). 
     The example sequence  600  may simplify branch device implementations, e.g., in the LTTPR devices, by allowing the device to be in a deeper sleep state for a longer time, thus allowing for better power management. For instance, in some cases, the DPTX and DPRX power savings achieved through the sequence  600  may remain unchanged from the example sequence  600  described above; however, the power savings in the LTTPRs may be doubled. However, there may be a latency overhead with a fully sequential wake such as the sequence  600 . For example, exit time (from sleep/standby) may be 60 uSec-70 uSec with an additional 60 uSec-70 uSec per LTTPR in the topology. 
     One or more of the following processes may be used to initiate power state transitions in devices of a DP-based link (e.g., a link between a video source device and display that is implemented based on a DisplayPort (DP) or embedded DisplayPort (eDP) specification (e.g., DP v2.1 or higher, or eDP v1.5 or higher)). The example processes may be implemented in software, firmware, hardware, or a combination thereof. In some embodiments, a computer-readable medium (e.g., volatile memory non-volatile memory, or a combination thereof) may be encoded with instructions that implement one or more of the operations in the example processes below. For example, in some embodiments, operations in the example processes shown in  FIGS. 7-8 , may be performed by one or more components of a video source device (e.g., GPU  144  of  FIG. 1 ). The example processes may include additional or different operations, and the operations may be performed in the order shown or in another order. In some cases, one or more of the operations shown in  FIGS. 7-8  are implemented as processes that include multiple operations, sub-processes, or other types of routines. In some cases, operations can be combined, performed in another order, performed in parallel, iterated, or otherwise repeated or performed another manner. 
       FIG. 7  is a flow diagram of an example process  700  of initiating a transition from an active link state to a low power link state in accordance with certain embodiments. The low power link state may refer to the scenario where devices of the DP link are transitioned into a low power state and transmit/output a common mode voltage rather than active signals (e.g., video signals) on the DP link. 
     At  702 , the video display source decides to transition to the low power link state. The determination may be made for any suitable reason. At  704 , one or more sleep signal patterns are transmitted over the DP link. The sleep pattern may be formatted as described above with respect to  FIG. 2 . As described above with respect to  FIG. 2 , the number of sleep patterns transmitted by the video source device or intermediate devices may be dependent on the number of devices of the DP link. In some instances, scrambled zeroes may be transmitted between each sleep pattern transmitted. At  706 , after the required number of sleep patterns are transmitted on the DP link, the video source device transitions into the low power state and outputs a common mode voltage on the link (i.e., does not transmit video signals or other data on the link). 
       FIG. 8  is a flow diagram of an example process  800  of initiating a transition from a low power link state to an active link state in accordance with certain embodiments. The active link state may refer to the scenario where devices of the DP link are transitioned into or are in an active power state and transmit/output active data signals (e.g., video signals) on the DP link. 
     At  802 , the video display source decides to transition to the active link state. The determination may be made for any suitable reason. At  804 , a wake pulse sequence is transmitted on the DP link. The wake pulse sequence may be formatted as described above with respect to segment  320  of  FIG. 3 . In some embodiments, a period of “silence” (i.e., the common mode voltage may be transmitted on the link) may follow the wake pulse sequence as described above with respect to  FIGS. 3-4 . At  806 , a physical link establishment signal pattern is transmitted on the link. The physical link establishment pattern may be formatted as described above with respect to  FIGS. 3-4 . At  808 , a clock establishment signal pattern is transmitted on the link. The clock establishment signal pattern may be formatted as described above with respect to  FIGS. 3-4 . Finally, at  810 , video signals are transmitted on the DP link. 
       FIGS. 9-10  are block diagrams of example computer architectures that may be used in accordance with embodiments disclosed herein. For example, in some embodiments, a computer system (e.g., a computer system  100 ) may contain one or more aspects shown in  FIGS. 9-10  (e.g., video source device  104  may be implemented with one or more components shown in  FIGS. 9 and 10 ) and may implement one or more aspects of the present disclosure. Other computer architecture designs known in the art for processors and computing systems may also be used. Generally, suitable computer architectures for embodiments disclosed herein can include, but are not limited to, configurations illustrated in  FIGS. 9-10 . 
       FIG. 9  is an example illustration of a processor according to an embodiment. Processor  900  is an example of a type of hardware device that can be used in connection with the implementations above. Processor  900  may be any type of processor, such as a microprocessor, an embedded processor, a digital signal processor (DSP), a network processor, a multi-core processor, a single core processor, or other device to execute code. Although only one processor  900  is illustrated in  FIG. 9 , a processing element may alternatively include more than one of processor  900  illustrated in  FIG. 9 . Processor  900  may be a single-threaded core or, for at least one embodiment, the processor  900  may be multi-threaded in that it may include more than one hardware thread context (or “logical processor”) per core. 
       FIG. 9  also illustrates a memory  902  coupled to processor  900  in accordance with an embodiment. Memory  902  may be any of a wide variety of memories (including various layers of memory hierarchy) as are known or otherwise available to those of skill in the art. Such memory elements can include, but are not limited to, random access memory (RAM), read only memory (ROM), logic blocks of a field programmable gate array (FPGA), erasable programmable read only memory (EPROM), and electrically erasable programmable ROM (EEPROM). 
     Processor  900  can execute any type of instructions associated with algorithms, processes, or operations detailed herein. Generally, processor  900  can transform an element or an article (e.g., data) from one state or thing to another state or thing. 
     Code  904 , which may be one or more instructions to be executed by processor  900 , may be stored in memory  902 , or may be stored in software, hardware, firmware, or any suitable combination thereof, or in any other internal or external component, device, element, or object where appropriate and based on particular needs. In one example, processor  900  can follow a program sequence of instructions indicated by code  904 . Each instruction enters a front-end logic  906  and is processed by one or more decoders  908 . The decoder may generate, as its output, a micro operation such as a fixed width micro operation in a predefined format, or may generate other instructions, microinstructions, or control signals that reflect the original code instruction. Front-end logic  906  also includes register renaming logic  910  and scheduling logic  912 , which generally allocate resources and queue the operation corresponding to the instruction for execution. 
     Processor  900  can also include execution logic  914  having a set of execution units  916   a ,  916   b ,  916   n , etc. Some embodiments may include a number of execution units dedicated to specific functions or sets of functions. Other embodiments may include only one execution unit or one execution unit that can perform a particular function. Execution logic  914  performs the operations specified by code instructions. 
     After completion of execution of the operations specified by the code instructions, back-end logic  918  can retire the instructions of code  904 . In one embodiment, processor  900  allows out of order execution but requires in order retirement of instructions. Retirement logic  920  may take a variety of known forms (e.g., re-order buffers or the like). In this manner, processor  900  is transformed during execution of code  904 , at least in terms of the output generated by the decoder, hardware registers and tables utilized by register renaming logic  910 , and any registers (not shown) modified by execution logic  914 . 
     Although not shown in  FIG. 9 , a processing element may include other elements on a chip with processor  900 . For example, a processing element may include memory control logic along with processor  900 . The processing element may include I/O control logic and/or may include I/O control logic integrated with memory control logic. The processing element may also include one or more caches. In some embodiments, non-volatile memory (such as flash memory or fuses) may also be included on the chip with processor  900 . 
       FIG. 10  illustrates a computing system  1000  that is arranged in a point-to-point (PtP) configuration according to an embodiment. In particular,  FIG. 10  shows a system where processors, memory, and input/output devices are interconnected by a number of point-to-point interfaces. Generally, one or more of the computing systems described herein may be configured in the same or similar manner as computing system  1000 . 
     Processors  1070  and  1080  may also each include integrated memory controller logic (MC)  1072  and  1082  to communicate with memory elements  1032  and  1034 . In alternative embodiments, memory controller logic  1072  and  1082  may be discrete logic separate from processors  1070  and  1080 . Memory elements  1032  and/or  1034  may store various data to be used by processors  1070  and  1080  in achieving operations and functionality outlined herein. 
     Processors  1070  and  1080  may be any type of processor, such as those discussed in connection with other figures. Processors  1070  and  1080  may exchange data via a point-to-point (PtP) interface  1050  using point-to-point interface circuits  1078  and  1088 , respectively. Processors  1070  and  1080  may each exchange data with a chipset  1090  via individual point-to-point interfaces  1052  and  1054  using point-to-point interface circuits  1076 ,  1086 ,  1094 , and  1098 . Chipset  1090  may also exchange data with a co-processor  1038 , such as a high-performance graphics circuit, machine learning accelerator, or other co-processor  1038 , via an interface  1039 , which could be a PtP interface circuit. In alternative embodiments, any or all of the PtP links illustrated in  FIG. 10  could be implemented as a multi-drop bus rather than a PtP link. 
     Chipset  1090  may be in communication with a bus  1020  via an interface circuit  1096 . Bus  1020  may have one or more devices that communicate over it, such as a bus bridge  1018  and I/O devices  1016 . Via a bus  1010 , bus bridge  1018  may be in communication with other devices such as a user interface  1012  (such as a keyboard, mouse, touchscreen, or other input devices), communication devices  1026  (such as modems, network interface devices, or other types of communication devices that may communicate through a computer network  1060 ), audio I/O devices  1016 , and/or a data storage device  1028 . Data storage device  1028  may store code  1030 , which may be executed by processors  1070  and/or  1080 . In alternative embodiments, any portions of the bus architectures could be implemented with one or more PtP links. 
     The computer system depicted in  FIG. 10  is a schematic illustration of an embodiment of a computing system that may be utilized to implement various embodiments discussed herein. It will be appreciated that various components of the system depicted in  FIG. 10  may be combined in a system-on-a-chip (SoC) architecture or in any other suitable configuration capable of achieving the functionality and features of examples and implementations provided herein. 
     While some of the systems and solutions described and illustrated herein have been described as containing or being associated with a plurality of elements, not all elements explicitly illustrated or described may be utilized in each alternative implementation of the present disclosure. Additionally, one or more of the elements described herein may be located external to a system, while in other instances, certain elements may be included within or as a portion of one or more of the other described elements, as well as other elements not described in the illustrated implementation. Further, certain elements may be combined with other components, as well as used for alternative or additional purposes in addition to those purposes described herein. 
     Further, it should be appreciated that the examples presented above are non-limiting examples provided merely for purposes of illustrating certain principles and features and not necessarily limiting or constraining the potential embodiments of the concepts described herein. For instance, a variety of different embodiments can be realized utilizing various combinations of the features and components described herein, including combinations realized through the various implementations of components described herein. Other implementations, features, and details should be appreciated from the contents of this Specification. 
     Although this disclosure has been described in terms of certain implementations and generally associated methods, alterations and permutations of these implementations and methods will be apparent to those skilled in the art. For example, the actions described herein can be performed in a different order than as described and still achieve the desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve the desired results. In certain implementations, multitasking and parallel processing may be advantageous. Additionally, other user interface layouts and functionality can be supported. Other variations are within the scope of the following claims. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any embodiments or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     The following examples pertain to embodiments in accordance with this Specification. It will be understood that certain examples may be combined with certain other examples, in certain embodiments. 
     Example 1 includes an apparatus comprising: a port comprising circuitry to couple the apparatus to one or more devices over a DisplayPort (DP)-based link; a processor to generate signals for communication over the DP-based link; and memory comprising instructions to cause the processor to: initiate a transition to a low power state in devices of the DP-based link by transmitting a sleep pattern signal over the DP-based link; and initiate a transition to an active power state in devices of the DP-based link by transmitting a wake pulse sequence and physical link establishment signal pattern over the DP-based link. 
     Example 2 includes the subject matter of Example 1 and/or other Example(s), and optionally, wherein the instructions are to transmit the sleep pattern over the DP-based link a number of times equal to the number of devices on the DP-based link other than the apparatus. 
     Example 3 includes the subject matter of Example 1 or 2 and/or other Example(s), and optionally, wherein each sleep pattern is 80 bits in 8b/10b encoding. 
     Example 4 includes the subject matter of Example 1 or 2 and/or other Example(s), and optionally, wherein each sleep pattern is 129 bits in 128b/132b encoding. 
     Example 5 includes the subject matter of Example 2 and/or other Example(s), and optionally, wherein the instructions are to transmit scrambled zeroes between each of the transmitted sleep patterns. 
     Example 6 includes the subject matter of Example 5 and/or other Example(s), and optionally, wherein the scrambled zeroes are at least 2560 bits in in 8b/10b encoding. 
     Example 7 includes the subject matter of Example 5 and/or other Example(s), and optionally, wherein the scrambled zeroes are at least 4096 bits in 128b/132b encoding. 
     Example 8 includes the subject matter of any one of Examples 1-7 and/or other Example(s), and optionally, wherein the instructions are to transmit a wake pulse sequence that includes a number of fixed length pulses. 
     Example 9 includes the subject matter of Example 8 and/or other Example(s), and optionally, wherein the instructions are to transmit at least seven pulses having a pulse length between 25 ns-50 ns. 
     Example 10 includes the subject matter of Example 8 and/or other Example(s), and optionally, wherein the instructions are to transmit the wake pulse sequence over a period of 175 ns-400 ns. 
     Example 11 includes the subject matter of any one of Examples 1-10 and/or other Example(s), and optionally, wherein the instructions are to output a common mode voltage between the wake pulse sequence and the physical link establishment signal pattern. 
     Example 12 includes the subject matter of Example 11 and/or other Example(s), and optionally, wherein the instructions are to output the common mode voltage over a period of 80 ns-120 ns. 
     Example 13 includes the subject matter of any one of Examples 1-12 and/or other Example(s), and optionally, wherein the instructions are to initiate the transition to the active power state by further transmitting signals to establish a clock signal in the devices of the DP-based link. 
     Example 14 includes the subject matter of any one of Examples 1-13 and/or other Example(s), and optionally, wherein the instructions are to cause the processor to transmit a common mode voltage over the DP-based link in the low power state, and transmit video signals over the DP-based link in the active power state. 
     Example 15 includes one or more computer-readable media comprising instructions that, when executed by a machine, cause the machine to: cause a video source device coupled to a display over a DisplayPort (DP)-based link to initiate a transition to a low power state in devices of the DP-based link by transmitting a sleep pattern signal over the DP-based link; and cause the video source device to initiate a transition to an active power state in the devices of the DP-based link by transmitting a wake pulse sequence and physical link establishment signal pattern over the DP-based link. 
     Example 16 includes the subject matter of Example 15 and/or other Example(s), and optionally, wherein the instructions are to transmit the sleep pattern over the DP-based link a number of times equal to the number of devices on the DP-based link other than the apparatus. 
     Example 17 includes the subject matter of Example 15 or 16 and/or other Example(s), and optionally, wherein each sleep pattern is 80 bits in 8b/10b encoding. 
     Example 18 includes the subject matter of Example 15 or 16 and/or other Example(s), and optionally, wherein each sleep pattern is 129 bits in 128b/132b encoding. 
     Example 19 includes the subject matter of Example 16 and/or other Example(s), and optionally, wherein the instructions are to transmit scrambled zeroes between each of the transmitted sleep patterns. 
     Example 20 includes the subject matter of Example 19 and/or other Example(s), and optionally, wherein the scrambled zeroes are at least 2560 bits in in 8b/10b encoding. 
     Example 21 includes the subject matter of Example 19 and/or other Example(s), and optionally, wherein the scrambled zeroes are at least 4096 bits in 128b/132b encoding. 
     Example 22 includes the subject matter of any one of Examples 15-21 and/or other Example(s), and optionally, wherein the instructions are to transmit a wake pulse sequence that includes a number of fixed length pulses. 
     Example 23 includes the subject matter of Example 22 and/or other Example(s), and optionally, wherein the instructions are to transmit at least seven pulses having a pulse length between 25 ns-50 ns. 
     Example 24 includes the subject matter of Example 22 and/or other Example(s), and optionally, wherein the instructions are to transmit the wake pulse sequence over a period of 175 ns-400 ns. 
     Example 25 includes the subject matter of any one of Examples 15-24 and/or other Example(s), and optionally, wherein the instructions are to output a common mode voltage between the wake pulse sequence and the physical link establishment signal pattern. 
     Example 26 includes the subject matter of Example 25 and/or other Example(s), and optionally, wherein the instructions are to output the common mode voltage over a period of 80 ns-120 ns. 
     Example 27 includes the subject matter of any one of Examples 15-26 and/or other Example(s), and optionally, wherein the instructions are to initiate the transition to the active power state by further transmitting signals to establish a clock signal in the devices of the DP-based link. 
     Example 28 includes the subject matter of any one of Examples 15-27 and/or other Example(s), and optionally, wherein the instructions are to cause the processor to transmit a common mode voltage over the DP-based link in the low power state, and transmit video signals over the DP-based link in the active power state. 
     Example 29 includes a system comprising: a display; and a video source device coupled to the display over a DisplayPort (DP)-based link, the video source device comprising circuitry to: initiate a transition to a low power state in devices of the DP-based link by transmitting a sleep pattern signal over the DP-based link; and initiate a transition to an active power state in devices of the DP-based link by transmitting a wake pulse sequence and physical link establishment signal pattern over the DP-based link. 
     Example 30 includes the subject matter of Example 29 and/or other Example(s), and optionally, wherein the circuitry is to initiate the transition to the active power state by further transmitting signals to establish a clock signal in the devices of the DP-based link. 
     Example 31 includes the subject matter of Example 29 or 30 and/or other Example(s), and optionally, wherein the system comprises one or more intermediate devices between the display and the video source device in the DP-based link. 
     Example 32 includes the subject matter of Example 31 and/or other Example(s), and optionally, wherein the circuitry is to transmit the sleep pattern signal a number of times equal to one more than the number of intermediate devices. 
     Example 33 includes the subject matter of Example 31 and/or other Example(s), and optionally, wherein each intermediate device is to transmit the wake pulse sequence to a downstream device of the DP-based link in response to detecting the wake pulse sequence transmitted by an upstream device of the DP-based link. 
     Example 34 includes the subject matter of Example 31 and/or other Example(s), and optionally, wherein each intermediate device is to transmit the wake pulse sequence to a downstream device of the DP-based link based on detecting the wake pulse sequence and physical link establishment signal pattern transmitted by an upstream device of the DP-based link. 
     Example 35 includes the subject matter of Example 29 and/or other Example(s), and optionally, wherein the circuitry is to transmit the sleep pattern over the DP-based link a number of times equal to the number of devices on the DP-based link other than the apparatus. 
     Example 36 includes the subject matter of Example 29 or 35 and/or other Example(s), and optionally, wherein each sleep pattern is 80 bits in 8b/10b encoding. 
     Example 37 includes the subject matter of Example 29 or 35 and/or other Example(s), and optionally, wherein each sleep pattern is 129 bits in 128b/132b encoding. 
     Example 38 includes the subject matter of Example 35 and/or other Example(s), and optionally, wherein the instructions are to transmit scrambled zeroes between each of the transmitted sleep patterns. 
     Example 39 includes the subject matter of Example 38 and/or other Example(s), and optionally, wherein the scrambled zeroes are at least 2560 bits in in 8b/10b encoding. 
     Example 40 includes the subject matter of Example 38 and/or other Example(s), and optionally, wherein the scrambled zeroes are at least 4096 bits in 128b/132b encoding. 
     Example 41 includes the subject matter of any one of Examples 29-40 and/or other Example(s), and optionally, wherein the instructions are to transmit a wake pulse sequence that includes a number of fixed length pulses. 
     Example 42 includes the subject matter of Example 41 and/or other Example(s), and optionally, wherein the instructions are to transmit at least seven pulses having a pulse length between 25 ns-50 ns. 
     Example 43 includes the subject matter of Example 41 and/or other Example(s), and optionally, wherein the instructions are to transmit the wake pulse sequence over a period of 175 ns-400 ns. 
     Example 44 includes the subject matter of any one of Examples 29-43 and/or other Example(s), and optionally, wherein the instructions are to output a common mode voltage between the wake pulse sequence and the physical link establishment signal pattern. 
     Example 45 includes the subject matter of Example 44 and/or other Example(s), and optionally, wherein the instructions are to output the common mode voltage over a period of 80 ns-120 ns. 
     Example 46 includes the subject matter of any one of Examples 29-45 and/or other Example(s), and optionally, wherein the instructions are to initiate the transition to the active power state by further transmitting signals to establish a clock signal in the devices of the DP-based link. 
     Example 47 includes the subject matter of any one of Examples 29-46 and/or other Example(s), and optionally, wherein the instructions are to cause the processor to transmit a common mode voltage over the DP-based link in the low power state, and transmit video signals over the DP-based link in the active power state. 
     Example 48 includes a method of initiating a transition to an active power state in devices of a DisplayPort (DP)-based link, comprising: transmitting a wake pulse sequence from a video source device over a DisplayPort (DP)-based link; transmitting a physical link establishment signal pattern over the DP-based link; transmitting a CDS signal pattern over the DP-based link; and transmitting a video signal over the DP-based link. 
     Example 49 includes the subject matter of Example 48 and/or other Example(s), and optionally, wherein the instructions are to transmit a wake pulse sequence that includes a number of fixed length pulses. 
     Example 50 includes the subject matter of Example 49 and/or other Example(s), and optionally, wherein the instructions are to transmit at least seven pulses having a pulse length between 25 ns-50 ns. 
     Example 51 includes the subject matter of Example 49 and/or other Example(s), and optionally, wherein the instructions are to transmit the wake pulse sequence over a period of 175 ns-400 ns. 
     Example 52 includes the subject matter of Example 48 and/or other Example(s), and optionally, wherein the instructions are to output a common mode voltage between the wake pulse sequence and the physical link establishment signal pattern. 
     Example 53 includes the subject matter of Example 52 and/or other Example(s), and optionally, wherein the instructions are to output the common mode voltage over a period of 80 ns-120 ns. 
     Example 54 includes the subject matter of Example 48 and/or other Example(s), and optionally, wherein the instructions are to initiate the transition to the active power state by further transmitting signals to establish a clock signal in the devices of the DP-based link. 
     Example 55 includes the subject matter of Example 48 and/or other Example(s), and optionally, further comprising transmitting a sleep pattern over the DP-based link. 
     Example 56 includes the subject matter of Example 55 and/or other Example(s), and optionally, wherein the sleep pattern is transmitted a number of times equal to the number of devices on the DP-based link other than the apparatus. 
     Example 57 includes the subject matter of Example 55 or 56 and/or other Example(s), and optionally, wherein each sleep pattern is 80 bits in 8b/10b encoding. 
     Example 58 includes the subject matter of Example 55 or 56 and/or other Example(s), and optionally, wherein each sleep pattern is 129 bits in 128b/132b encoding. 
     Example 59 includes the subject matter of Example 56 and/or other Example(s), and optionally, wherein the instructions are to transmit scrambled zeroes between each of the transmitted sleep patterns. 
     Example 60 includes the subject matter of Example 59 and/or other Example(s), and optionally, wherein the scrambled zeroes are at least 2560 bits in in 8b/10b encoding. 
     Example 61 includes the subject matter of Example 59 and/or other Example(s), and optionally, wherein the scrambled zeroes are at least 4096 bits in 128b/132b encoding. 
     Example 62 includes an apparatus for implementing any method as disclosed herein. 
     Example 63 includes one or more computer-readable media comprising instructions that, when executed by a machine, cause the machine to implement any method as disclosed herein. 
     Thus, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results.