Abstract:
The present invention relates to methods and systems for updating a buffer. In one aspect, the present invention provides a method for updating a buffer, which includes strategically writing to the buffer to enable concurrent read and write to the buffer. The method eliminates the need for double buffering, thereby resulting in implementation cost and space savings compared to conventional buffering approaches. The method also prevents image tearing when used to update a frame buffer associated with a display, but is not limited to such applications. In another aspect, the present invention provides efficient mechanisms to enable buffer update across a communication link. In one example, the present invention provides a method for relaying timing information across a communication link.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority to Provisional Application No. 60/630,853 entitled “MDDI Host Core Design” filed Nov. 24, 2004, Provisional Application No. 60/631,549 entitled “Mobile Display Digital Interface Host Camera Interface Device” filed Nov. 30, 2004, Provisional Application No. 60/632,825 entitled “Camera MDDI Host Device” filed Dec. 2, 2004, Provisional Application No. 60/633,071 entitled “MDDI Overview” filed Dec. 2, 2004, Provisional Application No. 60/633,084 entitled “MDDI Host Core Pad Design” filed Dec. 2, 2004, and Provisional Application No. 60/632,852 entitled “Implementation of the MDDI Host Controller” filed Dec. 2, 2004, and assigned to the assignee hereof and hereby expressly incorporated by reference herein in their entirety.  
         [0002]     The present application is also related to commonly assigned U.S. Pat. No. 6,760,772 B2, titled “Generating and Implementing a Communication Protocol and Interface for High Speed Data Transfer”, issued Jul. 6, 2004, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates generally to methods and systems for updating a buffer. More particularly, the invention relates to methods and systems for updating a buffer across a communication link.  
         [0005]     2. Background of the Invention  
         [0006]     In the field of interconnect technologies, demand for ever increasing data rates, especially as related to video presentations, continues to grow.  
         [0007]     The Mobile Display Digital Interface (MDDI) is a cost-effective, low power consumption, transfer mechanism that enables very-high-speed data transfer over a short-range communication link between a host and a client. MDDI requires a minimum of just four wires plus power for bi-directional data transfer that delivers a maximum bandwidth of up to 3.2 Gbits per second.  
         [0008]     In one application, MDDI increases reliability and decreases power consumption in clamshell phones by significantly reducing the number of wires that run across a handset&#39;s hinge to interconnect the digital baseband controller with an LCD display and/or a camera. This reduction of wires also allows handset manufacturers to lower development costs by simplifying clamshell or sliding handset designs.  
         [0009]     In controlling an LCD display across an MDDI link, one problem that arises relates to image flickering when the display is refreshed. Typically, what is needed is either a long persistence conversion or a refresh rate that is higher than what the human eye can perceive. Long persistence conversion results in image smearing when images appear to move. Therefore, it is desirable for the display to have a high refresh rate. A typical problem that occurs, however, is image tearing. The problem is that while the display is being refreshed at a high rate, the frame buffer associated with the display is being filled at a slower rate. As a result, the display image may reflect both updated and old image information within the same frame of the display.  
         [0010]     In one solution, multiple buffers are used and image information is cycled through the multiple buffers to avoid the image tearing problem described above. This includes commonly known “double buffering” approaches. The drawback of such solution, however, is clearly in the increased cost and chip space requirements in implementation.  
         [0011]     What is needed therefore are methods and systems to enable buffer update solutions that solve the above described problems while satisfying the cost and space requirements of MDDI applications.  
       SUMMARY  
       [0012]     The present invention relates to methods and systems for updating a buffer.  
         [0013]     In one aspect, the present invention provides a method for updating a buffer, which includes strategically writing to the buffer to enable concurrent read and write to the buffer. The method eliminates the need for double buffering, thereby resulting in implementation cost and space savings compared to conventional buffering approaches. Among other advantages, the method prevents image tearing when used to update a frame buffer associated with a display, but is not limited to such applications.  
         [0014]     In another aspect, the present invention provides efficient mechanisms to enable buffer update across a communication link. In one example, the present invention provides a method for relaying timing information across a communication link. The method, however, is not limited to relaying timing information, and may be used in more general contexts as can be understood by persons skilled in the art(s) based on the teachings herein.  
         [0015]     Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.  
         [0017]      FIG. 1  is a block diagram that illustrates an example environment using a Mobile Display Digital Interface (MDDI) interface.  
         [0018]      FIG. 1A  is a diagram of a digital data device interface coupled to a digital device and a peripheral device.  
         [0019]      FIG. 2  is a block diagram that illustrates an MDDI link interconnection according to an embodiment of the example of  FIG. 1 .  
         [0020]      FIG. 3  is an example that illustrates the image tearing problem.  
         [0021]      FIG. 4  is a process flowchart that illustrates a method for updating a buffer according to the present invention.  
         [0022]      FIG. 5  illustrates examples of the method of  FIG. 4 .  
         [0023]      FIGS. 6A, 6B  illustrate buffer read/write strategies.  
         [0024]      FIG. 7  is a process flowchart that illustrates a method for conveying timing information across a communication link according to the present invention.  
         [0025]      FIG. 8  illustrates an example signal timing diagram for initiating MDDI link wakeup to convey timing information. 
     
    
       [0026]     The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.  
       DETAILED DESCRIPTION  
       [0027]     This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto.  
         [0028]     The embodiment(s) described, and references in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.  
         [0029]     Embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.  
         [0000]     Mobile Display Digital Interface (MDDI)  
         [0030]     The Mobile Display Digital Interface (MDDI) is a cost-effective, low power consumption, transfer mechanism that enables very-high-speed serial data transfer over a short-range communication link between a host and a client.  
         [0031]     In the following, examples of MDDI will be presented with respect to a camera module contained in an upper clamshell of a mobile phone. However, it would be apparent to persons skilled in the relevant art(s) that any module having functionally equivalent features to the camera module could be readily substituted and used in embodiments of this invention.  
         [0032]     Further, according to embodiments of the invention, an MDDI host may comprise one of several types of devices that can benefit from using the present invention. For example, the host could be a portable computer in the form of a handheld, laptop, or similar mobile computing device. It could also be a Personal Data Assistant (PDA), a paging device, or one of many wireless telephones or modems. Alternatively, the host could be a portable entertainment or presentation device such as a portable DVD or CD player, or a game playing device. Furthermore, the host can reside as a host device or control element in a variety of other widely used or planned commercial products for which a high speed communication link is desired with a client. For example, a host could be used to transfer data at high rates from a video recording device to a storage based client for improved response, or to a high resolution larger screen for presentations. An appliance such as a refrigerator that incorporates an onboard inventory or computing system and/or Bluetooth connections to other household devices, can have improved display capabilities when operating in an internet or Bluetooth connected mode, or have reduced wiring needs for in-the-door displays (a client) and keypads or scanners (client) while the electronic computer or control systems (host) reside elsewhere in the cabinet. In general, those skilled in the art will appreciate the wide variety of modern electronic devices and appliances that may benefit from the use of this interface, as well as the ability to retrofit older devices with higher data rate transport of information utilizing limited numbers of conductors available in either newly added or existing connectors or cables. At the same time, an MDDI client may comprise a variety of devices useful for presenting information to an end user, or presenting information from a user to the host. For example, a micro-display incorporated in goggles or glasses, a projection device built into a hat or helmet, a small screen or even holographic element built into a vehicle, such as in a window or windshield, or various speaker, headphone, or sound systems for presenting high quality sound or music. Other presentation devices include projectors or projection devices used to present information for meetings, or for movies and television images. Another example would be the use of touch pads or sensitive devices, voice recognition input devices, security scanners, and so forth that may be called upon to transfer a significant amount of information from a device or system user with little actual “input” other than touch or sound from the user. In addition, docking stations for computers and car kits or desk-top kits and holders for wireless telephones may act as interface devices to end users or to other devices and equipment, and employ either clients (output or input devices such as mice) or hosts to assist in the transfer of data, especially where high speed networks are involved. However, those skilled in the art will readily recognize that the present invention is not limited to these devices, there being many other devices on the market, and proposed for use, that are intended to provide end users with high quality images and sound, either in terms of storage and transport or in terms of presentation at playback. The present invention is useful in increasing the data throughput between various elements or devices to accommodate the high data rates needed for realizing the desired user experience.  
         [0033]      FIG. 1A  is a diagram of a digital data device interface  100  coupled to a digital device  150  and a peripheral device  180 . Digital device  150  can include, but is not limited to, a cellular telephone, a personal data assistant, a smart phone or a personal computer. In general digital device  150  can include any type of digital device that serves as a processing unit for digital instructions and the processing of digital presentation data. Digital device  150  includes a system controller  160  and a link controller  170 .  
         [0034]     Peripheral device  180  can include, but is not limited to, a camera, a bar code reader, an image scanner, an audio device, and a sensor. In general peripheral  180  can include any type of audio, video or image capture and display device in which digital presentation data is exchanged between a peripheral and a processing unit. Peripheral  180  includes control blocks  190 . When peripheral  180  is a camera, for example, control blocks  190  can include, but are not limited to lens control, flash or white LED control and shutter control. Digital presentation data can include digital data representing audio, image and multimedia data.  
         [0035]     Digital data interface device  100  transfers digital presentation data at a high rate over a communication link  105 . In one example, an MDDI communication link can be used which supports bi-directional data transfer with a maximum bandwidth of 3.2 Gbits per second. Other high rates of data transfer that are higher or lower than this example rate can be supported depending on the communications link. Digital data interface device  100  includes a message interpreter module  110 , a content module  120 , a control module  130  and a link controller  140 .  
         [0036]     Link controller  140 , which is located within digital data interface  100 , and link controller  170 , which is located within digital device  150  establish communication link  105 . Link controller  140  and link controller  170  may be MDDI link controllers.  
         [0037]     The Video Electronics Standards Association (“VESA”) MDDI Standard, which is incorporated herein by reference in its entirety, describes the requirements of a high-speed digital packet interface that lets portable devices transport digital images from small portable devices to larger external displays. MDDI applies a miniature connector system and thin flexible cable ideal for linking portable computing, communications and entertainment devices to emerging products such as wearable micro displays. It also includes information on how to simplify connections between host processors and a display device, in order to reduce the cost and increase the reliability of these connections. Link controllers  140  and  170  establish communication path  105  based on the VESA MDDI Standard.  
         [0038]     U.S. Pat. No. 6,760,772, entitled Generating and Implementing a Communication Protocol and Interface for High Data Rate Signal Transfer, issued to Zou et al. on Jul. 6, 2004 (&#39;772 Patent”) describes a data interface for transferring digital data between a host and a client over a communication path using packet structures linked together to form a communication protocol for presentation data. Embodiments of the invention taught in the &#39;772 Patent are directed to an MDDI interface. The signal protocol is used by link controllers, such as link controllers  140  and  170 , configured to generate, transmit, and receive packets forming the communications protocol, and to form digital data into one or more types of data packets, with at least one residing in the host device and being coupled to the client through a communications path, such as communications path  105 .  
         [0039]     The interface provides a cost-effective, low power, bi-directional, high-speed data transfer mechanism over a short-range “serial” type data link, which lends itself to implementation with miniature connectors and thin flexible cables. An embodiment of link controllers  140  and  170  establishes communication path  105  based on the teachings of the &#39;772 Patent. The &#39;772 Patent is herein incorporated by reference in its entirety.  
         [0040]     In other embodiments, link controllers  140  and  170  can both be a USB link controller or they both can include a combination of controllers, such as for example, an MDDI link controller and another type of link controller, such as, for example, a USB link controller. Alternatively, link controllers  140  and  170  can include a combination of controllers, such as an MDDI link controller and a single link for exchanging acknowledgement messages between digital data interface device  100  and digital device  150 . Link controllers  140  and  170  additionally can support other types of interfaces, such as an Ethernet or RS-232 serial port interface. Additional interfaces can be supported as will be known by individuals skilled in the relevant arts based on the teachings herein.  
         [0041]     Within digital data interface device  100 , message interpreter module  110  receives commands from and generates response messages through communication link  105  to system controller  160 , interprets the command messages, and routes the information content of the commands to an appropriate module within digital data interface device  100 .  
         [0042]     Content module  120  receives data from peripheral device  180 , stores the data and transfers the data to system controller  160  through communication link  105 .  
         [0043]     Control module  130  receives information from message interpreter  130 , and routes information to control blocks  190  of peripheral device  180 . Control module  130  can also receive information from control blocks  190  and routes the information to the message interpreter module  110 .  
         [0044]      FIG. 1  is a block diagram that illustrates an example environment using an MDDI interface. In the example of  FIG. 1 , MDDI is used to interconnect modules across the hinge of a clamshell phone  100 .  
         [0045]     Referring to  FIG. 1 , a lower clamshell section  102  of clamshell phone  100  includes a Mobile Station Modem (MSM) baseband chip  104 . MSM  104  is a digital baseband controller. An upper clamshell section  114  of clamshell phone  100  includes a Liquid Crystal Display (LCD) module  116  and a camera module  118 .  
         [0046]     Still referring to  FIG. 1 , an MDDI link  110  connects camera module  118  to MSM  104 . Typically, an MDDI link controller is integrated into each of camera module  118  and MSM  104 . In the example of  FIG. 1 , an MDDI Host  122  is integrated into camera module  112 , while an MDDI Client  106  resides on the MSM side of the MDDI link  110 . Typically, the MDDI host is the master controller of the MDDI link. In the example of  FIG. 1 , pixel data from camera module  118  are received and formatted into MDDI packets by MDDI Host  122  before being transmitted onto MDDI link  110 . MDDI client  106  receives the MDDI packets and re-converts them into pixel data of the same format as generated by camera module  118 . The pixel data are then sent to an appropriate block in MSM  104  for processing.  
         [0047]     Still referring to  FIG. 1 , an MDDI link  112  connects LCD module  116  to MSM  104 . In the example of  FIG. 1 , MDDI link  112  interconnects an MDDI Host  108 , integrated into MSM  104 , and an MDDI Client  120  integrated into LCD module  116 . In the example of  FIG. 1 , image data generated by a graphics controller of MSM  104  are received and formatted into MDDI packets by MDDI Host  108  before being transmitted onto MDDI link  112 . MDDI client  120  receives the MDDI packets and re-converts them into image data for use by LCD module  116 . Typically, image data is buffered using a frame buffer before being used to refresh the LCD display.  
         [0048]      FIG. 2  is a block diagram that illustrates MDDI link interconnection  112  according to the example of  FIG. 1 . As described above, one of the functions of MDDI link  112  is to transfer image data from MSM  104  to LCD Module  116 . A frame interface (not shown in  FIG. 2 ) connects MDDI link controller  120  to modules of LCD Module  116 . Similarly, another frame interface (not shown in  FIG. 2 ) connects MDDI link controller  108  to appropriate modules of MSM  104 . Typically, MDDI link controller  108  represents the host controller of the MDDI link, while MDDI link controller  120  represents the client controller of the MDDI. Other implementations, however, may reverse the roles of the two controllers.  
         [0049]     MDDI link  112  includes a minimum of four wires, comprising two wires for data signals  202  and  204  and two wires for probe signals  206  and  208 , in addition to two wires for power signals  210  and  211 . Data signals  202  and  204  are bi-directional. Accordingly, data can be transmitted in either direction (from host to client and vice versa) using data signals  202  and  204 . Strobe signals  206  and  208  are unidirectional, and may only be driven by the host controller of the link. Accordingly, in the example of  FIG. 2 , only host controller  108  may drive strobe signals  206  and  208 .  
         [0000]     Method and Systems for Updating a Buffer  
         [0050]     As described above, MDDI can be used to connect a baseband processor (MSM  104  in  FIG. 2 , for example) and a graphics controller (LCD module  116  in  FIG. 2 , for example). The baseband processor channels image information, typically received from a camera sensor, to the graphics controller, which uses the image information to create a display image. Typically, the graphics controller employs one or more frame buffers to store the image information received from the baseband processor before using it to generate the display image. As described above, image tearing is one problem that occurs. This happens when the image information is being read out of the frame buffer at a rate slower or faster than the rate at which it is being written to the frame buffer. Methods and systems for updating a buffer, which, among other advantages, solve the image tearing problem, will be described herein. It should be noted, however, that methods and systems according to the present invention are not limited to the specific exemplary embodiments in which they will described or to being used in an MDDI environment. Further, methods and systems of the present invention can be employed in various other applications that utilize buffering, and that may benefit from the advantages of the present invention.  
         [0000]     Image Tearing  
         [0051]      FIG. 3  illustrates two examples of image tearing that can occur while reading from and/or writing to a buffer. The diagram of  FIG. 3  shows plots of read and write pointers as functions of buffer position and time. The read pointer represents the position in the buffer that is being read. The write pointer indicates the position in the buffer that is being written to. In the example of  FIG. 3 , the buffer position is defined in terms of pixel position in the buffer.  
         [0052]     In the first example in  FIG. 3 , the buffer is being read at a slower rate than it is written to. This is illustrated by the relative slopes of read and write pointer lines  302  and  304 . Note that read and write pointer lines  302  and  304  intersect at time t 0 . Before time t 0 , pixels in the buffer are being read prior to being updated. After time t 0 , pixels are being updated prior to be read. Accordingly, within the same frame (from time  0  to time t 1 ), pixels in positions  0  to p 0  (which corresponds to the pixel position read at time t 0 ) are read with older image information relative to pixels from position p 0  to the last pixel in the buffer, which are read with updated image information. The result is image tearing with a lower portion of the image reflecting newer image information relative to an upper portion of the image.  
         [0053]     In the second example in  FIG. 3 , the buffer is being read at a faster rate than it is written to. This is illustrated by the relative slopes of read and write pointer lines  302  and  306 . Read and write pointer lines  302  and  306  intersect at time t 2 . Before time t 2 , pixels in the buffer are being updated prior to being read. After time t 2 , pixels are being read prior to being updated. Accordingly, within the same frame (from time t 1  to time t 3 ), pixels in positions  0  to p 2  (which corresponds to the pixel position read at time t 2 ) are read with newer image information relative to pixels from position p 2  to the last pixel in the buffer, which are read with old image information. The result is image tearing with an upper portion of the image reflecting newer image information relative to a lower portion of the image.  
         [0000]     Method for Updating a Buffer  
         [0054]     A method to strategically update a buffer will now be provided. The method prevents image tearing when used to update a frame buffer associated with a display. The method may also be used in other buffering applications based on its apparent advantages as will be described herein.  
         [0055]      FIG. 4  is a process flowchart  400  that illustrates a method for updating a buffer according to the present invention. Process flowchart  400  begins in step  410 , which includes determining a read line position in the buffer. The read line position indicates a line currently being read from the buffer. Typically, step  410  is achieved by determining the value of a read pointer that points to the read line position in the buffer.  
         [0056]     Step  420  includes partitioning the buffer into at least a first section that is safe to update and a second section that must not be updated based on the read line position. It is noted here that partitioning the buffer does not refer here to a physical but to a logical partitioning of the buffer. Further, a logical partition of the buffer is not fixed and may change as will be understood from the teachings herein. The first section of the buffer includes lines of the buffer that have been read within the current buffer reading cycle based on the read line position. The first section also includes lines of the buffer that can be updated based on the read line position. In other words, the first section includes lines whose content has just been read or lines that can be updated prior to the read line position reaching them based on the buffer read speed and the buffer write speed. Lines that cannot be updated prior to the read line position reaching them based on the buffer read speed and the buffer write speed belong to the second section of the buffer. In other words, lines of the second section of the buffer are those for which there is not sufficient time to update before they have to be read. Accordingly, lines of the second section of the buffer must have been updated during the last reading cycle of the buffer.  
         [0057]     Step  430  includes updating the buffer by writing data at a line of the first section which follows the second section based on the read line position. Typically, the buffer is updated at a position which is both safe to update as described above and which has already been read during the last reading cycle of the buffer. In one embodiment, step  430  includes writing data at a line of the first section which immediately follows the last line of the second section. Other variations of step  430  may also be possible as will be apparent to a person skilled in the art based on the teachings disclosed herein.  
         [0000]     Example Illustration  
         [0058]      FIG. 5  provides examples that illustrate the method described above in  FIG. 4 .  FIG. 5  shows three examples A, B, and C of reading a buffer  500 . For purposes of illustration only, buffer  500  is shown to include  352  lines of data. A read pointer  510  indicates the read line position in the buffer. Sections labeled with the roman numeral “I” represent lines that belong to the first section of the buffer as described above. Sections labeled with the roman numeral “II” represent lines that belong to the second section of the buffer as described above.  
         [0059]     In example A, shaded area “I” represents lines of the first section of the buffer which have already been read during the current reading cycle of the buffer. In the example, this area includes lines  1  through m- 1 . Read pointer  510  indicates that line m is currently being read. Accordingly, area “II” in example A represents lines of buffer  500  that cannot be updated based on the current position of read pointer  510 . In other words, there is no sufficient time to update lines in area “II” based on the current position of read pointer  510  and the read and write speeds to the buffer. Note that the first section of the buffer also includes an unshaded area “I” below area “II”. This area “I” belongs to the first section as it is safe to update, but should not be updated given that it has not been read during the current reading cycle of the buffer. Updating unshaded area “I” prior to reading it would result in image tearing, as described in  FIG. 3 , where the upper portion of the image reflects older image information relative to the lower portion of the image.  
         [0060]     In example B, the shaded area represents lines of the buffer which have already been read during the current reading cycle of the buffer. In the example, this area includes lines  1  through  351 . Read pointer  510  indicates that line  352  is currently being read. Accordingly, area “II” in example B represents lines that must have been updated given the current read line position. Lines in area “II” cannot be updated based on the current read line position and the read and write speeds to the buffer, and belong to the second section of the buffer based on the description above. Lines in area “I” belong to the first section of the buffer, and are safe to update. To update the buffer, writing can begin in area “I”. Data can be written at a line in area “I” that immediately follows area “II”. This corresponds to line m in example B.  
         [0061]     Example C illustrates a scenario subsequent to the one shown in B. In example C, read pointer  510  has wrapped around and is reading line m of the buffer. Accordingly, lines preceding the read pointer in the buffer belong to the first section of the buffer, and may be updated. Lines in area “II” must have been updated during the last write cycle to the buffer given the current read line position. Lines in area “II” cannot be updated, and belong to the second section of the buffer as described above. In other words, lines in area “II” must contain updated information given the read line position, as there is not sufficient time to update them before they have to be read. Shaded area “I” represents lines of the first section of the buffer that are safe to update, but should not be updated given that they have not been read during the last reading cycle of the buffer.  
         [0000]     Buffer Read/Write Strategies  
         [0062]     Buffer read/write strategies to avoid image tearing or equivalent problems related to buffer update are described herein. Buffer update strategies according to the present invention further eliminate the need for the commonly adopted “double buffering” technique. Instead, a single buffer is used, which results in both implementation cost and space savings. The present invention is not limited to the exemplary strategies described herein, and variations which are apparent to persons skilled in the art(s) are also considered to be within the scope of the present invention.  
         [0063]      FIGS. 6A and 6B  illustrate exemplary buffer read/write strategies according to the present invention. The diagrams of  FIGS. 6A and 6B  show plots of read pointer  612  and write pointers  614  and  616  as functions of buffer position and time. In the examples of  FIGS. 6A and 6B , the buffer position is defined in terms of pixel position in the buffer, which may be equivalently replaced with any other measure of buffer position, such as line number, for example.  
         [0064]     Referring to  FIG. 6A , an exemplary buffer read/write strategy is depicted over two reading cycles of the buffer. In the first reading cycle, from time  0  to time t 1 , the first half of the buffer is updated, while the entire buffer content is read. In the second reading cycle of the buffer, from time t 1  to time t 2 , the second half of the buffer is updated, while the entire buffer content is read. Note that the first half of the buffer, during the second reading cycle, contains updated information that were written to the buffer during the first reading cycle. The second half of the buffer, during the second cycle, is updated prior to being read as shown by write pointer  614  preceding read pointer  612  in time over the second reading cycle. Accordingly, over both reading cycles, data read from the buffer belongs to the same update cycle of the buffer, and no image tearing occurs.  
         [0065]      FIG. 6B  illustrates another exemplary buffer read/write strategy over two reading cycles of the buffer. During the first reading cycle, the first half of the buffer is updated from time t 0  to time t 1 . During the second reading cycle, the second half of the buffer is updated from time t 1  to time t 2 . Note that writing to the buffer starts at a time to during the first cycle such that, during the first cycle, the entire buffer is read with an initial information content and not an updated content due to the writing process. On the other hand, writing to the buffer ends at a time t 2  during the second cycle such that, during the second cycle, the entire buffer contains updated information content when it is read. This is shown by write pointer  616  preceding read pointer  612  in time over the second reading cycle. Accordingly, image tearing will not occur over both reading cycles in the example of  FIG. 6B .  
         [0000]     Buffer Update Through a Communication Link  
         [0066]     Methods and systems for updating a buffer according to the present invention may be used in a variety of applications. In one application, as described above, the buffer update approach may be used to update a frame buffer associated with a display. In another application, the buffer is updated remotely, wherein it is written to by a first processor and is read by a second processor, and wherein the first and second processors communicate through a communication link. For example, the first and second processors represent an MSM baseband processor and an LCD module, respectively, that communicate through an MDDI link, as illustrated in  FIG. 2 . In certain applications, synchronization between the first and second processors will be required.  
         [0067]     Methods and systems related to synchronization to enable buffer update across a communication link will now be provided. As will be understood by a person skilled in the art(s) based on the teachings herein, certain aspects of the methods and systems that will be presented may be applicable to synchronization problems in general, and are not limited to synchronization for enabling remote buffer update.  
         [0068]     In one aspect, synchronization between the first and second processors includes scheduling a first event at the first processor that is triggered by a second event at the second processor. This is typically done by writing to a register to enable the triggering of an interrupt that causes the first event at the first processor whenever the second event occurs at the second processor. For example, in a remote buffer update application, where the buffer is updated by the first processor and read by the second processor, the first event may represent the need to start writing to the buffer, while the second event may represent that the read pointer has finished a complete reading cycle of the buffer. The second event may then be triggered at the second processor based on the read line position in the buffer.  
         [0069]     In another aspect, methods to convey synchronization information across the communication link are provided. The methods may be employed to relay synchronization information related to buffer update, as described above, for example.  FIG. 7  is a process flowchart  700  that illustrates a method for conveying timing information across a communication link between a first processor and a second processor, when the communication link is in hibernation mode. Process flowchart  700  begins in step  710 , which includes scheduling a time event at the first processor to convey timing information to the second processor. The time event may be a periodic event as required by the specific application. For example, in the case of a buffer update application, the time event may be related to the read line position in the buffer.  
         [0070]     Step  720  includes initiating a link wakeup by the first processor at the occurrence of the time event. For example, in the case of a buffer update across an MDDI link, where an MDDI client is located at the LCD module side of the interconnection, the MDDI client may initiate a link wakeup by driving the data signal to a logic one to notify the MDDI host that the buffer should be updated.  
         [0071]     Subsequently, step  730  includes detecting the link wakeup at the second processor (for example, an MDDI host on the MSM side of the MDDI interconnection), and using the detected link wakeup timing to synchronize the first and second processors with respect to the timing information that is being conveyed. For example, in the case of a buffer update across an MDDI link, when the MDDI host detects the link wakeup by the MDDI client, it can synchronize itself with the MDDI client with respect to the buffer update start time.  
         [0072]     It can be appreciated by a person skilled in the art based on the teachings herein that the method described in  FIG. 7  may be extended to convey any kind of timing information across a communication link, and is not limited to buffer update synchronization purposes. The advantages of such method are through saving the link and conveying information by simply waking the link up.  
         [0073]      FIG. 8  illustrates an example timing diagram  800  for initiating link wakeup to convey timing information across an MDDI interconnection. For example, the MDDI interconnection may be such as the one described above with reference to  FIG. 2  with an MDDI host located at the MSM and an MDDI client located at the LCD module. The MDDI client, accordingly, would initiate a link wakeup to convey buffer update information to the MDDI host, which, in turn, would start refreshing the buffer located in the LCD module. In the example of  FIG. 8 , vsync_wake signal  802  represents a value written to a register at the MDDI host to enable a wakeup at the host based on vsync signal  806 . Wakeup at the host occurs whenever the value of vsync_wake  802  is high. Vsync signal  806  represents a value of a signal “vertical sync”, which occurs at the client and is related to buffer update time. For example, vsync  806  goes high whenever the read pointer has wrapped and is reading from the beginning of the buffer. Link_active signal  804  represents whether or not the data signal of the MDDI interconnection is active or in hibernation. Mddi_client_wakeup signal  808  represents a signal at the client, which responds to vsync  806  to wake up the client.  
         [0074]     In the example of  FIG. 8 , vsync_wake  802  is set at the host at time A. At time B, the MDDI link goes into hibernation mode. At time C, vsync  806  goes high indicating that the buffer needs to be refreshed by the host. As a result, mddi_client_wakeup  808  also goes high to wake the client up to initiate the link wakeup. The client initiates the link wakeup by driving the data signal of the interconnection, and the link goes active at time D. Subsequently, vsync_wake  802  and mddi_client_wakeup return to zero, and the host detects the link wakeup and begins to refresh the buffer at the client.  
         [0000]     Conclusion  
         [0075]     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.