Patent Publication Number: US-7721159-B2

Title: Passing debug information

Description:
CROSS REFERENCE AND INCORPORATION BY REFERENCE 
     This application is related in whole or in part to the following U.S. patent application Ser. Nos. 10/756,441, 10/756,439, 10/756,685, 10/756,435, 10/756,530, 10/756,529, 10/756,667, 10/756,600, 11/056,471, 11/056,066, and Ser. No. 11/056,472, and cross references and, herein, incorporates by reference, in their entirety, these applications. 
     FIELD OF INVENTION 
     The present invention relates to data communications architectures for computer processors and, more particularly, to communications architectures for computer processors employing serializers and deserializers. 
     BACKGROUND 
     Computing architectures that operate efficiently and that can process data quickly are generally preferred over their counterparts. The speed at which these computing architectures process data may be limited by a number of factors that include the design of the architecture, operating conditions, quality of utilized components, and the protocols, logic, and methodologies employed by the computer architecture when processing data. Latencies in the communication of data across components arising from data communications architectures and protocols of a computing architecture may also impact the speed at which data may be processed. 
     A number of data communications architectures are currently employed to communicate data between cooperating components of a computer architecture (e.g. computer processors within a computing environment&#39;s processing unit or between a computer processor and peripheral component such as a data storage device). For example, IDE/ATA (Integrated Drive Electronics/Advanced Technology Attachment) and SCSI (Small Computer Systems Interface) are both common interfaces to hard drives (as well as some other devices, such as CD-ROM and DVD drives), and there are several versions of each. Other data communications architectures include PCI (Peripheral Components Interconnect), AGP (Accelerated Graphics Port), USB (Universal Serial Bus), serial data communications ports, and parallel data communications ports. 
     Although each of the above data communications architectures are effective in transmitting data between cooperating components, each of these architectures have drawbacks, performance limitations and may not be reliable. Specifically, such data communication architectures are not designed to handle voluminous amounts of data communications, which are communicated at high clock frequencies (e.g. several Giga Hertz). Additionally, the PCI, IDE, and SCSI data communication architectures generally require overhead processing calculations when communicating data that impacts overall data communications speed. Stated differently, in addition to the desired data being communicated additional overhead processing data must be communicated. As such, less overall data is processed during each clock cycle. 
     Responsive to the need for higher bandwidth data communications architectures, the SERDES (serializer/deserializer) data communications architecture was developed. SERDES operates to encode and decode data according to a predefined scheme (e.g. eight-bit/ten-bit-8b10b encoding). The encoded data is communicated over one or more communication channels from the serializer to a corresponding deserializer for decoding. The SERDES data communication architecture has been shown to increase data communications bandwidth between cooperating components. In this context, SERDES data communication architectures are deployed as data buses operating to carry data between cooperating components. 
     SUMMARY 
     A data communications architecture employing serializers and deserializers for use in communicating data between computer processing components of a computing environment to reduce latency is provided. In an illustrative implementation, a data communications architecture comprises a data interface, a serializer and a deserializer. In operation, data from computer processing components is received by the serializer. The serializer cooperating with the data interface encodes the data for communication to the deserializer according to a selected encoding protocol. Operationally, the serializer and deserializer (SERDES) cooperate to form a communications link or communications channel. The data interface, among other things, allows for the collection of data to be transferred across the link from each end of the link, provides link management and control information, encodes error protection and provides logic for processing the data across the communications channel. 
     Further to the exemplary implementation, the illustrative data communications architecture further comprises data buffers, a training module, a debugging module, an error injection module and an error detection module. These monitors and/or modules comprise a portion of the serializer and the deserializer. In operation, these monitors and/or modules cooperate with the data interface and instruction sets contained in the serializer and deserializer to realize functions including, but not limited to, processing debug information, processing link identification information, injecting errors across communications links, and performing error detection. 
     Other features of the invention are further described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The data communications architecture and methods of use are further described with reference to the accompanying drawings in which: 
         FIG. 1  is a block diagram of an exemplary computing environment in accordance with an implementation of the herein described systems and methods; 
         FIG. 2  is a block diagram showing the cooperation of exemplary components of an exemplary data communications architecture; 
         FIG. 3  is a block diagram of a transmit core in accordance with an exemplary implementation of a data communications architecture; 
         FIG. 4  is a block diagram of a receiving core in accordance with an exemplary implementation of a data communications architecture; 
         FIG. 5  is a flowchart diagram showing the processing performed by an exemplary data communications architecture when communicating data; 
         FIG. 6  is a flowchart diagram showing the processing performed by an exemplary data communications architecture when handling debug information; 
         FIG. 7  is a flowchart diagram showing the processing performed by an exemplary data communications architecture when handling identification information; 
         FIG. 8  is a flowchart diagram showing the processing performed by an exemplary data communications architecture when injecting errors as part of a link test; and 
         FIG. 9  is a flowchart diagram showing the processing performed by an exemplary data communications architecture when handling error detection. 
     
    
    
     DETAILED DESCRIPTION 
     Overview: 
     To provide the infrastructure bandwidth needed by computing environments, implementations have turned to utilizing serializers/deserializers (SERDES) point to point data communications architectures operating at high frequencies. In applying the SERDES data communications architecture to a computing environment&#39;s internal data communications infrastructure, a number of limitations come to light. In general terms, unnecessary latency in data communications arise from inefficient data communications architecture management. The management of the SERDES data communications architecture may be performed by a data interface that, among other things, collects data for communication along the SERDES communication links and provides error detection and handling instructions for errant data. 
     The present invention provides a data interface for use by SERDES link channels that support operations occurring bi-directionally between data communications architecture components. In an illustrative implementation, a mechanism is provided to collect data for transfer across a SERDES link from each end of the link. Additionally the mechanism may operate to provide overlay link management information, to encode error detection, and to encode the data into the proper format. The data interface of the herein described illustrative implementation also maintains logic that directs SERDES components to collect, generate, embed, and/or communicate particular types of data (e.g. error detection information, link identification information, error information, and debugging information) between SERDES link components for reliability testing and/or characterization, debugging, link training, and to check that such data is correctly collected and communicated. 
     The illustrative SERDES data communications architecture may also employ a data buffer to store data. In operation, the data buffer may be used to store data until correct receipt is confirmed by a response from the receiving end of a SERDES communications link. In such case, an acknowledgement may be embedded as part of data communicated between cooperating components of the SERDES data communications architecture. When an error is detected by SERDES components, the data buffer may be used to resend the data to correct the error. 
     Furthermore, the illustrative implementation may orchestrate the use of multiple parallel SERDES communications channels. A SERDES communications channel may comprise a logical communications link operating on a physical link (e.g. wires) between SERDES components (e.g. serializers and deserializers). When performing error detection, and other operations, the illustrative SERDES data communications architecture may employ a spare channel. Additionally, such spare channel may be used to maintain communication availability even in the event of a hard failure of one of the channels. 
     Illustrative Computing Environment 
       FIG. 1  depicts an exemplary computing system  100  in accordance with herein described system and methods. Computing system  100  is capable of executing a variety of computing applications  180 . Exemplary computing system  100  is controlled primarily by computer readable instructions, which may be in the form of software, where and how such software is stored or accessed. Such software may be executed within central processing unit (CPU)  110  to cause data processing system  100  to do work. In many known computer servers, workstations and personal computers central processing unit  110  is implemented by micro-electronic chips CPUs called microprocessors. Coprocessor  115  is an optional processor, distinct from main CPU  110 , that performs additional functions or assists CPU  110 . CPU  110  may be connected to co-processor  115  through interconnect  112 . One common type of coprocessor is the floating-point coprocessor, also called a numeric or math coprocessor, which is designed to perform numeric calculations faster and better than general-purpose CPU  110 . 
     It is appreciated that although an illustrative computing environment is shown to comprise a single CPU  110  that such description is merely illustrative as computing environment  100  may comprise a number of CPUs  110 . Additionally computing environment  100  may exploit the resources of remote CPUs (not shown) through communications network  160  or some other data communications means (not shown). 
     In operation, CPU  110  fetches, decodes, and executes instructions, and transfers information to and from other resources via the computer&#39;s main data-transfer path, system bus  105 . Such a system bus connects the components in computing system  100  and defines the medium for data exchange. System bus  105  typically includes data lines for sending data, address lines for sending addresses, and control lines for sending interrupts and for operating the system bus. An example of such a system bus is the PCI (Peripheral Component Interconnect) bus. Some of today&#39;s advanced busses provide a function called bus arbitration that regulates access to the bus by extension cards, controllers, and CPU  110 . Devices that attach to these busses and arbitrate to take over the bus are called bus masters. Bus master support also allows multiprocessor configurations of the busses to be created by the addition of bus master adapters containing a processor and its support chips. 
     Memory devices coupled to system bus  105  include random access memory (RAM)  125  and read only memory (ROM)  130 . Such memories include circuitry that allows information to be stored and retrieved. ROMs  130  generally contain stored data that cannot be modified. Data stored in RAM  125  can be read or changed by CPU  110  or other hardware devices. Access to RAM  125  and/or ROM  130  may be controlled by memory controller  120 . Memory controller  120  may provide an address translation function that translates virtual addresses into physical addresses as instructions are executed. Memory controller  120  may also provide a memory protection function that isolates processes within the system and isolates system processes from user processes. Thus, a program running in user mode can normally access only memory mapped by its own process virtual address space; it cannot access memory within another process&#39;s virtual address space unless memory sharing between the processes has been set up. 
     In addition, computing system  100  may contain peripherals controller  135  responsible for communicating instructions from CPU  110  to peripherals, such as, printer  140 , keyboard  145 , mouse  150 , and data storage drive  155 . 
     Display  165 , which is controlled by display controller  163 , is used to display visual output generated by computing system  100 . Such visual output may include text, graphics, animated graphics, and video. Display  165  may be implemented with a CRT-based video display, an LCD-based flat-panel display, gas plasma-based flat-panel display, a touch-panel, or other display forms. Display controller  163  includes electronic components required to generate a video signal that is sent to display  165 . 
     Further, computing system  100  may contain network adaptor  170  which may be used to connect computing system  100  to an external communication network  160 . Communications network  160  may provide computer users with means of communicating and transferring software and information electronically. Additionally, communications network  160  may provide distributed processing, which involves several computers and the sharing of workloads or cooperative efforts in performing a task. It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used. 
     It is appreciated that exemplary computer system  100  is merely illustrative of a computing environment in which the herein described systems and methods may operate and does not limit the implementation of the herein described systems and methods in computing environments having differing components and configurations as the inventive concepts described herein may be implemented in various computing environments having various components and configurations. 
     Data Communications Architecture: 
       FIGS. 2-4  depict block diagrams of an illustrative data communications architecture for use in an exemplary computing environment. The illustrative data communications architecture may be implemented as components of the computing environment and may employ SERDES components. Specifically,  FIG. 2  shows a block diagram of illustrative data communications architecture  200 . As is shown in  FIG. 2 , data communications architecture  200  comprises data communications interface modules  205  and  210  cooperating to communicate data  230  over physical links  220 . Data interface communications modules  205  and  210  comprise at least one transmit core and at least one receiving core. Physical links  220  attach to data communications interface modules  205  and  210  through physical connectors  225 . 
     In operation, exemplary computing environment (not shown) cooperates with data communications interface modules  205  and  210  to communicate data between data communications interface modules  205  and  210 . In the illustrative implementation, data communication interface modules may reside in disparate geographic locations within exemplary computing environment (not shown) or may reside as part of one of exemplary computing environment&#39;s (not shown) printed circuit boards (PCB). As is shown, data may be communicated in a selected direction or bi-directionally, as indicated by the arrows  232  and  234  on physical links  220  and data  230 , between transmit cores and receiving cores of data communications interfaces  205  and  210 . Also, it is appreciated that physical links  220  are depicted having differing line thickness to indicate different physical link  220  media. 
     Furthermore, as is shown, dashed box  215  shows the components of an exemplary data communications back plane. In the implementation provided, back plane  215  is shown to have a pair of transmit-receive cores operating to communicate data. Specifically, data is processed by transmit core  235  of data communications interface  205  for communication through physical connector  225  and physical links  220  to receiving core  245  of data communications interface  210 . Similarly, data may be processed for communication by transmit core  250  of data communications interface  210  to receiving core  240  of data communications interface  205 . Moreover, transmit-receiving core pairs  235 ,  240  and  245 ,  250  may cooperate to form a communications channel. As a communications channel the transmit-receive core pairs may be aligned and trained to process data according to a selected encoding protocol such as eight-bit-ten-bit (8b10b) encoding. 
     Further, as is shown in  FIG. 2 , data  230  may comprise a number of packets. Specifically, data  230  may contain a header portion and data packet portion. The data packet portion may further contain small data packets. It is appreciated that in the illustrative implementation provided, a small packet may be considered a data packet that is smaller in size than a normal, full sized data packet. In operation, various data, control, training, and channel management information may be communicated over exemplary data communications architecture  200  as data  230 . 
       FIG. 3  shows a block diagram of exemplary transmit core environment  300  depicting its components and their cooperation. As is shown in  FIG. 3 , exemplary transmit core environment  300  comprises a plurality of transmit cores ranging from transmit core  300 - 1  to transmit core  300 - n.  Transmit core  300 - 1  is shown to comprise logic block a plurality of serializers and drivers from serializer  1  to serializer n, and driver  1  to driver m, respectively. Additionally, transmit core  300 - 1  cooperates with an external data communications component (not shown) to obtain clock signal CLK. Also, as is shown, transmit core  300 - 1  comprises logic which maintains instruction sets to instruct the components of transmit core  300 - 1  (e.g. serializer  1 ) to perform functions in accordance with data communications operations. The logic of transmit core  300 - 1  may also act to maintain one or more modules and mechanisms for use during data communications operations including, but not limited to, data buffers (not shown), a debugging module  305 , a training module  310 , an error injection module  315  and an error detection module  320 . 
     In operation, data is provided as input to one of transmit core  300 - 1 &#39;s serializers. The data is encoded according to a selected encoding protocol (e.g. 8 bit-10 bit encoding) and is prepared for communication to a cooperating data communications component by one of the transmit core&#39;s drivers at one of the transmit core&#39;s output channels. The encoding protocol may employ CLK signal to encode a number of bits within a selected cycle(s) of the CLK signal. For example, Data A may be encoded by serializer  1  of transmit core  300 - 1  according to a selected encoding protocol and prepared for communication by driver  1  to produce Encoded Data at channel A output as per instructions provided by transmit core  300 - 1 &#39;s logic. Similarly, Data B may be encoded by serializer  2  of transmit core  300 - 1  according to a selected encoding protocol and prepared for communication by driver  2  to produce Encoded Data at channel B. Such encoding process and data communication preparation is performed across the remaining serializers and drivers of transmit core  300 - 1  and the other transmit cores of transmit core environment  300 . 
       FIG. 4  shows a block diagram of exemplary receiving core environment  400  depicting its components and their cooperation. As is shown in  FIG. 4 , exemplary receiving core  400  comprises a plurality of receiving cores ranging from receiving core  400 - 1  to receiving core  400 - n.  Receiving core  400 - 1  is shown to comprise a logic block a plurality of deserializers and drivers from deserializer  1  to deserializer n, and from driver  1  to driver m, respectively. Additionally, receiving core  400 - 1  cooperates with an external data communications component (not shown) to obtain clock signal CLK. Also, as is shown, receiving core  400 - 1  comprises logic which maintains instruction sets to instruct the components of receiving core  400 - 1  (e.g. deserializer  1 ) to perform functions in accordance with data communications operations. The logic of receiving core  400 - 1  may also act to maintain one or more modules and mechanisms for use during data communications operations including, but not limited to, data buffers (not shown), a debugging module  405 , a training module  410 , an error injection module  415  and an error detection module  420 . 
     In operation, encoded data is provided as input to one of receiving core  400 - 1 &#39;s deserializers. The data is decoded according to a selected decoding protocol (e.g. 10 bit-8 bit) and is prepared for communication by one of the receiving core&#39;s drivers to a cooperating data communications component at one of the receiving core&#39;s deserializer&#39;s outputs. The decoding protocol may employ a CLK signal to decode a number of bits within a selected cycle(s) of the CLK signal. For example, Encoded Data A may be decoded by deserializer  1  of receiving core  400 - 1  according to a selected decoding protocol and prepared for communication by driver  1  to produce Data A as per instructions provided by receiving core  400 - 1 &#39;s logic. Similarly, Encoded Data B may be decoded by deserializer  2  of receiving core  400 - 1  according to a selected decoding protocol and prepared for communication by driver  2  to produce Data B. Such decoding process and data communication preparation is performed across the remaining deserializers and drivers of receiving core  400 - 1  and the other receiving cores of transmit core environment  400 . 
     Taken together  FIG. 3  and  FIG. 4  describe an exemplary communications channel environment such that data is encoded for communication by one or more transmit cores for decoding and subsequent processing by one or more receiving cores. Although described as separate components, it is appreciated that transmit cores and receiving cores may reside on a single communications component (see data communications interface  205  of  FIG. 2 ). Moreover, transmit cores and receiving cores may operate as pairs to form one or more bi-directional data communications channels. 
     Communicating Data Across Communications Links: 
       FIG. 5  shows the processing performed by exemplary data communications architecture  200  when establishing a communications channel. As is shown, processing begins at block  500  and proceeds to block  505  where the communications components are powered up for operation. From there, processing proceeds to block  510  where communications links are established between the data communication architecture components. The communications links are then trained at block  515  to form a communications channel. Training data is then sent over the communications channel at block  520  to test the communications channel. A check is then performed at block  525  to determine if the communications channel test was successful. If it was successful, processing proceeds to block  540  where a check is performed to determine if there is stream of data to communicate over the successfully tested communications channel. If at block  540  it is determined that there is no data to communicate, processing reverts to the input of block  540 . However, if there is a stream of data to communicate over the successfully tested and trained communications channel, processing proceeds to block  545  where the stream of data is encoded by serializers. The encoded stream of data is then communicated over the communications channel to cooperating deserializers at block  550 . The stream of data is then decoded by the deserializers at block  555 . A check is then performed at block  560  to determine if each small data packet of the stream of data was successfully communicated. If the small data packet was successfully transmitted, processing reverts to block  540  and proceeds there from. However, if the small data packet was not successfully communicated, processing reverts back to block  530  where the communications channel is retrained and continues from there. 
     However, if at block  525  it is determined that the communications channel test was not successful, processing proceeds to block  530  where the communications links are retrained. From there processing proceeds to block  535  where control information is communicated between the communications link components. From there, processing reverts to block  520  and proceeds there from. 
     In operation, the illustrative implementation provides that the training sequence is governed by the deserializers of a communications link. Specifically, initial training is deemed completed upon the recognition of an indication of the writing of a selected software type register on the deserializer. At such time, data is driven onto the link by the serializers of the communications channel. In the context of deserializer operations, the deserializers maintain one or more instructions sets which direct the deserializers to detect activity on the link to signal cooperating serializers to begin initialization. The deserializers and serializers of the communications channels maintain at least one instruction set to direct the channels to power up. Upon successful power up, a per channel self test is performed from which the results are collected and compared. The instruction set then directs the serializers and deserializers to communicate a selected data pattern which is expected by the deserializers which allow the deserializers to determine bit units grouping for use by the encoding and decoding protocols utilized by the serializers and deserializers. 
     Additionally, a second recognizable data pattern is communicated to the deserializers which the deserializers attribute as the small packet data communications. By setting the small packet data communications the deserializers can operate to match small packets together in groupings consistent with how the small packets were originally communicated. Once the second data pattern is successfully communicated and processed, a control signal is sent from the deserializers to the serializers of the communications links indicating that training has been completed. At this point data packets may be communicated across the trained channels. 
     Moreover, the illustrative implementation provides that should an error occur over the communications link, the link may perform a retraining process. Link retraining is similar to the above-described link training outside of foregoing the powering up the communication channel components. Retraining may be triggered by a number of events, including but not limited to, the recognition of an error across the communications link or by reception of an error signal on the link generated by the receiving end of the communications link. 
     Debug Operations: 
     Exemplary data communications architecture  200  of  FIG. 2  is also capable of passing debug data for processing and analysis. In the context of a SERDES data communications architecture, more visibility into the internal design of the exemplary data communications architecture can translate into more efficient debug and validation of the SERDES data communications architecture design and implementation. In the SERDES data communications architecture, during debug operation, debug data is routed across the various components of the architecture for processing and analysis. Proper staging and off-loading of the debug information occurs when the debug data is successfully propagated across the architecture. 
     In the implementation provided, the debug data may originate from an internal debug data hardware component comprising a portion of either of the transmit core ( 300  of  FIG. 3 ) or receiving core ( 400  of  FIG. 4 ). The debug data is processed according to one or more instruction sets to propagate the debug data among the cooperating components of the exemplary communications architecture. In the implementation provided the exemplary architecture may receive debug data having a first selected number of bits and pair such debug data to create a modified debug data (e.g. debug data packet) having a second selected number of bits. The paired debug data may then be buffered to match it to a communication link frequency and then communicated across the communication link. On the receiving end, the paired debug data may be captured and decomposed to a data packet having the first selected number of bits. 
     Included in the debug operations may be the capability by the receiving end of an exemplary communications link of the exemplary communications architecture to collect regular non-debug transactions of the link and provide all, or part, of the non-debug transactions to the internal debug logic for subsequent communication (e.g. transaction data repeated on a different exemplary outbound link of the exemplary communications architecture). In doing so, the debug logic contributes to more efficient processing and communication of data across the exemplary data communications architecture. 
     Additionally, the illustrative implementation provides that the transmit end of the communications link may either pair alternating cycles of the internal debug data hardware component as a debug data packet, or it may utilize a valid indication sent along with the debug data to match up debug data being forwarded from a cooperating data communications architecture component (e.g. a link port). Furthermore, the illustrative implementation provides that the exemplary data communications architecture may enter debug operations through the initiation of a link retraining. Upon completion of the link training sequence, debug operations proceed. 
       FIG. 6  shows the processing performed by exemplary data communications architecture  200  when handling debug data. As is shown, processing begins at block  600  and proceeds to block  610  where the debug data, having an original selected number of bits (e.g. 76 bits), is paired up to generate a debug data packet having a second selected number of bits (e.g. 152 bits). From there, the debug data packet is buffered to match it up to the communications link frequency at block  615 . The debug data packet is then communicated across the communications link at block  620 . From there the debug data packet is captured and processed at the receiving end of the communications link at block  625 . 
     A check is then performed at block  640  to determine if there are link malfunctions. If the check at block  640  indicates a link malfunction, processing proceeds to block  645  where the malfunction is reported for further action. Processing then proceeds to block  660  where the communications link is retrained. From there processing reverts to block  610  and continues from there. 
     However, if at block  640  it is determined that there are no link malfunctions, processing proceeds to block  635  where the debug data packet is decomposed to put in a form where the debug data has its original number of selected bits. From there, processing proceeds to block  650  to continue with data transactions. Processing then terminates at block  655 . 
     Link Identification Information: 
     Exemplary data communications architecture  200  is also capable of passing link identification information. The illustrative implementation operates to allow for the confirmation, validation, and mapping of the physical communications links of exemplary communications data architecture  200  through the use of link identification information. 
     In the context of a SERDES data communications architecture, several links are used together for each point to point connection within the exemplary data communications architecture. In the illustrative implementation, the communication nodes of a SERDES data communications architecture may be connected into crossbar hardware components which facilitate the communication of data across a SERDES data communications architecture. These physical connections direct and dictate the operation of the exemplary data communications architecture. To ensure that these connections are correct, and/or to build a mapping of the connections, knowledge about the connections is required. 
     The illustrative implementation provides that the communications links of the exemplary data communications architecture may be trained prior to use. During training, among other things, the exemplary data communications architecture, identifies the placement of the clocks of the various cooperating components of the data communications architecture. Using the clock position information, data packets may be aligned from the transmitting end to the receiving end of the communications link ensuring cohesive data communications. 
     The illustrative implementation further provides that, in operation, a location identifier is generated and communicated from the transmitting end of an exemplary communications link to the receiving end of the communications link providing location (e.g. mapping and connection) information about the transmitting end of the communications link. In the illustrative implementation, the location identifier may be embedded in the training sequence at some selected interval or training step but prior to the link being released for normal operation. The embedded location identifier is captured by the receiving end as per the receiving end&#39;s logic (e.g. instructions sets and commands), during the training sequence, placing the location identification signal in a storage component for subsequent processing. In this context, the exemplary data communications architecture may utilize one or more instruction sets to process the location identification information (e.g. through the use of internal or external software) to generate a topology of the data communication architecture connections and connection relationships. 
     Specifically, the data pattern (e.g. location identifier) to be passed through the transmitting end of the communications link may be hard-wired by hardware logic and/or be programmable via an instruction set (e.g. software) or may be provided by external sources such as cooperating hardware components. The illustrative implementation provides that the location identifier data field may be of the programmable kind loaded into the receiving end by shifting in the data pattern (e.g. location identifier) from an external input communications port that may be driven by one or more field programmable gate arrays (FPGA) (not shown). In being of the programmable type, the data pattern may include additional information about the physical connection beyond just location, including but not limited to, hardware type (e.g. chip type), link frequency and link status. In the context of status information, such information may include, but is not limited to, reset progress, port status, configuration information or error status. 
       FIG. 7  shows the processing performed by exemplary data communications architecture  200  when passing link identification information. As is shown, processing begins at block  700  and proceeds to block  705  where data communications architecture initiates training of the communications link. From there processing proceeds to block  710  where a location identifier is obtained that identifies the relative position of the transmitting end to the receiving end of an exemplary communications link. At block  715  the location identifier is embedded as part of the training sequence of the communications link. Processing then proceeds to block  720  where the location identifier is captured ad processed by the receiving end of the communications link. The location identifier value is compared with an expected value at block  725  by the receiving end of the communications link. 
     A check is then performed at block  830  to determine if there were any errors in the transmission of the location identifier. If there were no errors determined at block  830 , processing proceeds to block  735  where training is completed and data transactions performed at block  745 . 
     However, if at block  730  it is determined that there were errors, processing proceeds to block  750  where the error is reported. The errors are then resolved at block  755 . From there, processing proceeds to block  705  and continues from there. 
     Error Injection: 
     Exemplary data communications architecture  200  of  FIG. 2  is also capable of injecting selected errors as part of communications link test. In the context of a SERDES data communications architecture, the illustrative implementation validates error case functionality in a system under evaluation (e.g. testing of a communications link). 
     SERDES data communications architectures provide for several different correctness checks of the data received at the receiving end of a communications link. Different actions are expected based on the nature of the error, and different information can be expected at the receiving end of the communications link. The illustrative implementation specifies a variety of injected error events triggered by a signal from the debug logic (e.g.  315  of  FIG. 3 ) found on the transmitting end of the communications link. For example such error events may include, but are not limited to, simple single bit errors, skipping or adding a small data packet, and turning off a communications link channel. 
     Additionally, the illustrative implementation provides for more than one error to be injected as part of a test sequence. In this context, a subsequent error may be injected so that it occurs simultaneously with the first error, or when a second trigger occurs. With such capability multiple error events are capable of being tested. Additionally, the illustrative implementation may allow for the specification of the duration of each error type. This may be from one to several cycles, or permanent (e.g. until the condition is cleared off the communications link). As such the illustrative implementation is capable of handling of both sporadic and stuck-at type failures. Moreover, the illustrative implementation may capture the corrupted small data packets in a buffer (e.g.  300  of  FIG. 3 ) on the transmit end of the communications link when an error trigger occurs. In doing so, a reference may be created to compare to the captured error logs at the receiving end of the link to confirm expected communications link behavior. 
       FIG. 8  shows the processing performed by exemplary data communications architecture  200  of  FIG. 2  when injecting errors as part of a communications link test. As is shown, processing begins at block  800  and proceeds to block  805  where a communication link is established. From there, processing proceeds to block  810  where one or more errors (e.g. stall, time lapse, incorrect small data packet, etc.) are generated for injection into data to be communicated from the transmitting end to the receiving end of the communications link. Processing then proceeds to block  815  where the generated errors are injected into the data. The modified data is then communicated across the communications link at block  820 . The error(s) are then captured on the receiving end of the communications link at block  825 . The captured errors are then analyzed to compare with original injected errors at block  830 . Based on the comparisons, the communications link operation is verified at block  835 . A check is then performed at block  840  to determine if the link is behaving as expected. If the check at block  840  indicates that the communications link is behaving as expected, processing terminates at block  850 . 
     However, if at block  840  it is determined that the link is behaving incorrectly, processing proceeds to block  845  where the communications link malfunctions are analyzed. From there, processing terminates at block  850 . 
     Error Detection: 
     Exemplary data communications architecture  200  of  FIG. 2  is also capable of efficiently detecting errors in data communication transactions without introducing latency into the communications link. In the context of a SERDES data communications architecture, the illustrative implementation is capable of retrying data transfers that fail to accurately pass across a SERDES communications link. 
     In SERDES data communications architectures, data packets may be tracked and monitored to determine successful transmission. In this context, the tag of selected small data packet that cross the link are monitored to determine successful transmission from the transmitting end of the communications link to the receiving end of the communications link. Upon successful transmission, an acknowledgement message may be sent from the receiving end of the communications link to the transmitting end of the communications link to indicate a successful transmission. As described previously, transactions may be sent across the communications link as a sequence of small data packets: one header small data packet with routing and transaction and transaction type information followed by as many additional sequence of small data packets as are necessary to complete the data transfer. In the illustrative implementation, the header may include the current small data packet tag. 
     In operation, the receiving end of the link checks the tag included in the header packets and flags a link error if the expected tag is not found. As such, an error due to a dropped or repeated small data packet will be discovered when the next small data packet expected to be a header does not have the correct tag. However, inefficiencies may result as an error may not be detected until the full transaction is completed. 
     The illustrative implementation provides the capability of including bits of the implied tag into the parity field(s) used to protect the small data packets for bit errors. In operation, the bits of the tag are included in a different one of the parity bits calculated to detect bit errors. As such, lost or repeated small data packets will result in a parity calculation error on the receiving end of the communications link. The illustrative implementation, upon detecting a parity error, may request the retransmission of the small data packet and may also prevent corrupted data from being forwarded from the receiving end of the communications link. 
       FIG. 9  shows the processing performed by exemplary data communications architecture  200  of  FIG. 2  when detecting errors in data communications transactions. As is shown, processing begins at block  900  and proceeds to block  905  where a communications link is established. From there processing proceeds to block  910  where the tag bits of the data-implied tag are generated. The generated tag bits are then encoded (e.g. calculate eight parity bits across the channels carrying data wherein each parity bit is based off the 1, 2, 3, . . . 8 th  bit of the 8 bits of data sent on a communications link) into the parity bit calculation on the transmitting end of the communications link at block  915 . From there, processing proceeds to block  920  where the data having the encoded tag bits as part of the parity bits is communicated across the communications link. The data is received at the receiving end of the communications link and the parity of the data is calculated by the receiving end at block  925 . A check is then performed at block  930  to determine if there are any errors in the transmitted parity calculation and the received parity calculation. If at block  930  it is determined that there are no errors, processing proceeds to block  940  where the data communications transactions continue. Processing then terminates at block  945 . 
     However, if at block  930 , it is determined that there are errors processing proceeds to block  940  where a request for the retransmission of data is sent by the receiving end of the communications link to the transmitting end of the communications link. Processing then reverts back to block  910  and continues from there. 
     In sum, the herein described apparatus and methods provide a data communication architecture employing for use as a computing environments communication fabric that reduces data latency. It is understood, however, that the invention is susceptible to various modifications and alternative constructions. There is no intention to limit the invention to the specific constructions described herein. On the contrary, the invention is intended to cover all modifications, alternative constructions, and equivalents falling within the scope and spirit of the invention. 
     It should also be noted that the present invention may be implemented in a variety of computer environments (including both non-wireless and wireless computer environments), partial computing environments, and real world environments. The various techniques described herein may be implemented in hardware or software, or a combination of both. Preferably, the techniques are implemented in computing environments maintaining programmable computers that include a processor, a storage medium readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device. Computing hardware logic cooperating with various instructions sets are applied to data to perform the functions described above and to generate output information. The output information is applied to one or more output devices. Programs used by the exemplary computing hardware may be preferably implemented in various programming languages, including high level procedural or object oriented programming language to communicate with a computer system. Illustratively the herein described apparatus and methods may be implemented in assembly or machine language, if desired. In any case, the language may be a compiled or interpreted language. Each such computer program is preferably stored on a storage medium or device (e.g., ROM or magnetic disk) that is readable by a general or special purpose programmable computer for configuring and operating the computer when the storage medium or device is read by the computer to perform the procedures described above. The apparatus may also be considered to be implemented as a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner. 
     Although an exemplary implementation of the invention has been described in detail above, those skilled in the art will readily appreciate that many additional modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, these and all such modifications are intended to be included within the scope of this invention. The invention may be better defined by the following exemplary claims.