Patent Publication Number: US-2012042207-A1

Title: Methods and structures for testing sas-2 speed options in speed negotiation windows

Description:
RELATED APPLICATIONS  
     The patent application is related to co-pending, commonly owned patent application Ser. No. XX/YYY,YYY (06-2564) filed on the same day and entitled METHODS AND STRUCTURES FOR TESTING SAS TRANSCEIVER TRAINING OPTIONS IN SAS-2 TRAINING WINDOWS which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
     The invention relates to serial attached SCSI (“SAS”) communications and more specifically relates to improvements in use of SAS-2 speed negotiation windows to test various configurations of speed options for supported SAS speeds between two devices. 
     BACKGROUND  
     In SAS communications one or more SAS initiator devices may be coupled to one or more SAS target devices through zero or more SAS expanders to form a SAS domain. In general, SAS initiator devices may initiate or request an initial connection to a particular identified SAS target device. Prior to initiating or requesting such a connection, devices within the SAS domain must perform initial processing to establish one or more mutually supported speeds for communication between any pair of connected devices. In general, each SAS device (initiator, target, or expander) may support one or more SAS speeds for communication with other SAS devices coupled to its PHYs. SAS specifications provide for a variety of SAS speeds standardized for communications between SAS devices. Some devices may support only one or a few lower speeds, other devices may support only one or a few higher speeds, and many devices support a broad spectrum of high and/or low SAS speeds. 
     The process of establishing the mutually supported speeds that may be used for communication between any two devices is referred to as speed negotiation. In the currently evolving SAS-2 specifications, each device must support processing during a speed negotiation window. The speed negotiation process in the specification defines signals exchanged between a pair of SAS devices to determine one or more SAS speeds supported by both devices in a particular desired link. If multiple speeds are supported by both devices, the highest supported speed is generally utilized if performance is critical while a slower speed may be utilized if reliability is more important than communication speed. 
     As presently specified in the evolving SAS-2 specifications, processing during the speed negotiation window exchanges signals between a pair of SAS devices and simply identifies all the potential speeds that are supported by both devices. In addition to the SAS speed, the evolving SAS-2 specifications specify a number of speed options that may be modified in support of each SAS speed. These speed options include, for example, whether or not spread spectrum clocking is supported for each SAS speed, the type of spread spectrum clocking supported, and the logical link rate requested in support of SAS-2 multiplexing. The SAS-2 specifications and other related background material generally known to those of ordinary skill in the art is readily available at www.t10.org and other public locations and sites. 
     Interoperability of SAS devices from various vendors is an ongoing challenge. In particular, in view of the various speed options that may be specified for each SAS speed, the challenge of interoperability is further exacerbated. As presently specified in the evolving SAS-2 specifications, there is little assurance that a particular SAS speed, though mutually supported by both devices, will provide reliable exchanges between the pair of devices. One vendor may utilize particular default speed options settings while another vendor may prefer other default speed option settings for the same SAS speed. Nothing in the present evolving version of the SAS-2 specifications provides for relief from this interoperability challenge. 
     It is evident from the above discussion that an ongoing need exists to improve reliability of transfers between a pair of SAS devices by assuring that a mutually supported SAS speed will provide a desired level of both performance and reliability. 
     SUMMARY  
     The present invention solves the above and other problems, thereby advancing the state of the useful arts, by providing methods and associated structure to test all speed option settings for each mutually supported SAS speed between a pair of communicating SAS devices. Features and aspects hereof provide for such testing in conjunction with speed negotiation window processing between a pair of coupled SAS devices. Testing of each set of speed options for each mutually supported SAS speed may include the exchange of SCSI requests and responses between the pair of SAS devices. Results of the testing may then be utilized by automated or manual administrative procedures to select a preferred SAS speed and an associated set of preferred speed options for communication between the pair of SAS devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a block diagram of a SAS device enhanced in accordance with features and aspects hereof to test various configured sets of speed options for each supported SAS speed in speed negotiations. 
         FIGS. 2-5  are flowcharts of methods in accordance with features and aspects hereof to test various configured sets of speed options for each supported SAS speed in speed negotiations. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of an exemplary SAS device  100  enhanced in accordance with features and aspects hereof to perform testing of each supported SAS speed during the speed negotiation processing. The SAS device  100  may also be referred to herein as a “master” device in that, as regards the speed negotiation process, device  100  is the device controlling and performing the speed negotiation processing to determine which of its supported speeds are also supported by the attached SAS device. 
     SAS device  100  may include a speed negotiation element  102  for performing speed negotiation by participating in a speed negotiation window in accordance with SAS-2 specifications and in accordance with features and aspects hereof. SAS speed negotiation element  102  is coupled to and co-operable with PHY layer  104 . PHY layer  104  performs standard state machine processing as specified in the SAS specifications to control physical layer operation of the communication media coupling device  100  to other SAS device  120 . PHY layer  104  may include error counters  106  for counting the number of detected errors in the PHY layer communication processing. As will be discussed further herein below, the error counters may be used in accordance with features and aspects hereof to determine the success or failure of a particular SAS speed and each associated set of speed options for use between the master device  100  and the other SAS device  120 . 
     Speed negotiation element  102  within SAS device  100  may be associated with speed options testing element  108  adapted to test various sets of speed options for each SAS speed supported by master device  100 . The speed testing memory  110  may be used for storing information regarding various possible combinations of speed option settings and may be used for recording associated test results for each tested combination of speed settings for each SAS speed tested by speed options testing element  108  in conjunction with operation of speed negotiation element  102  on behalf of master device  100 . 
     In operation, SAS device  100 , when initialized such as at start of day or power on reset processing, first determines which of the various SAS speeds it supports are also supported by the other SAS device  120  coupled to its PHY layer  104 . Speed negotiation processing is generally specified by the SAS-2 specifications to be performed under a SAS-2 defined protocol during a speed negotiation window. As specified therein and as well known to those of ordinary skill in the art, SAS device  100  instructs its PHY layer  104  to exchange various signals with other SAS device  120  to indicate the supported speeds within master device  100 . Other SAS device  120  may respond with appropriate signals to indicate those speeds also supported by other SAS device  120 . In general, SAS device  100  may construct a list of mutually supported SAS speeds and then select from the list of supported speeds a preferred speed for operation of the communication link between SAS device  100  other such device  120 . 
     In accordance with features and aspects hereof, the list of mutually supported SAS speeds may be constructed and maintained in speed testing memory  110 . Further, speed options testing element  108  is operable to sequence through each of the mutually supported speeds and test every combination of speed options associated with each mutually supported speed. Those of ordinary skill in the art will readily recognize that every possible set of speed options may be configured and tested or some lesser subset of the possible combinations of options may be tested. The lesser subset of possible speed options may be determined as appropriate for the particular application of the SAS device  100 . For example, certain application environments known to require higher reliability and/or known to be particularly noisy environments may avoid utilizing higher speed, lower reliability speed options settings. Or, for example, portable applications having limited power may utilize only speed options settings that help conserve scarce power resources. The particular sets of speed options to be tested may be selected as a matter of design choice well known to those of ordinary skill in the art. 
     As noted above and as discussed further herein below, speed options testing element  108  may be operable to test each SAS speed and each combination of associated speed options by transmitting suitable SCSI requests from the master device  100  to the other SAS device  120 . The request and corresponding response may be exchanged with each configured set of speed options for each mutually supported SAS speed. The SCSI request is communicated from SAS device  100  to other SAS device  120 . The response generated therefrom is evaluated by SAS device  100  to determine the success or failure of the particular configured set of speed options at the particular, configured, mutually supported SAS speed. 
     Operation of speed options testing element  108  may utilize speed testing memory  110  to construct a list of the supported SAS speeds and combinations of sets of speed options. The resulting list indicates SAS speeds and associated speed option settings that are not only mutually supported but also verified by testing of speed options testing element  108 . The resulting list of tested, verified SAS speeds and associated speed options settings may be communicated to an administrative process or user to select a speed for the particular application of SAS device  100 . Further, the list of tested and supported SAS speeds may also be utilized by an automated process or agent within SAS device  100  to automatically select among the options represented by the list of supported, tested SAS speeds and associated speed option settings. The selection of a supported/tested SAS speed and speed option setting may therefore be performed by any suitable means as a matter of design choice. 
     Those of ordinary skill in the art will readily recognize that the particular functional/modular decomposition of functional and physical elements within SAS device  100  is intended merely as exemplary of one possible embodiment of features and aspects hereof. Numerous alternative and equivalent functional and modular decompositions will be readily apparent to those of ordinary skill in the art as a matter of design choice. In particular, the integration or separation of speed negotiation element  102  relative to PHY layer  104  may be determined as a matter of design choice in a particular embodiment of features and aspects hereof. 
       FIG. 2  is a flowchart describing a method in accordance with features and aspects hereof for improved speed negotiation within a master SAS device. In accordance with features and aspects hereof, the master device performs speed negotiation and test processing  200 . Speed negotiation processing of element  200  is generally in accordance with the SAS-2 specifications while test processing of element  200  is in accordance with enhanced features and aspects hereof. As is known to those of ordinary skill in the art, the SAS-2 specifications call for speed negotiation to be performed by participating in a speed negotiation window defined as an aspect of the SAS protocol. Signals are exchanged between the master SAS device and an attached SAS device during the negotiation window to determine a list of mutually supported SAS speeds. In accordance with features and aspects hereof the speed negotiation and test element  200  is enhanced to include testing of each mutually supported SAS speed at each of one or more possible combinations of SAS speed options. Thus, speed negotiation and test element  200  includes iterative steps to test each mutually supported SAS speed and to generate a list of mutually supported SAS speeds that have passed the test to verify operation at the associated speed. 
     Element  202  is first operable to determine whether additional SAS speeds supported by the master SAS device remain to be negotiated and tested to verify mutual support by the other SAS device and to verify proper operation of the mutually supported speeds. If no further SAS speeds remain to be negotiated and tested, processing of element  200  is complete and the master SAS device continues with normal operation to complete initialization of the SAS device and to perform desired application specific communications between the master SAS device and the other SAS device connected thereto. If element  202  determines that more SAS speeds need to be evaluated, element  204  is operable to perform standard SAS-2 compliant negotiation by participating in a speed negotiation window. Element  204  thereby determines whether the other SAS device also supports the current speed selected for testing in the master SAS device. Element  206  then determines whether the speed negotiation processing of element  204  determined that the SAS speed being evaluated is also supported by the other SAS device. If not, processing continues looping back to element  202  until all SAS speeds supported by the master device have been negotiated and tested. 
     If element  206  determines that the speed negotiation identified a mutually supported SAS speed for the master SAS device and the other SAS device couple thereto, element  208  is next operable to test the link (e.g., utilizing the PHY layer communications) to test actual operation of the link utilizing the negotiated, mutually supported speed. Details of the processing of element  208  are discussed further herein below with respect to  FIG. 3 . Element  210  is then operable to update the list of mutually supported SAS speeds with the test results generated by operation of element  208 . As noted above, operation of element  200  establishes a list of mutually supported SAS speeds and stores the test results associated with the each mutually supported SAS speed. An administrative user or process may then manually or automatically select among the mutually supported, tested speeds to determine the preferred or optimal speed for the particular application of the master SAS device. Processing then continues looping back to element  202  until all SAS speeds are negotiated and tested to generate the list of mutually supported SAS speeds and associated test results. 
       FIG. 3  provides exemplary additional details of the processing of element  208  of  FIG. 2  to test a mutually supported negotiated SAS speed. Elements  300  through  312  are iteratively operable to evaluate each possible combination or set of SAS speed options for the current SAS speed being evaluated (e.g. the SAS speed just negotiated to identify it as mutually supported by both SAS devices). Element  300  first determines whether additional sets or combinations of speed options remain to be tested for this current SAS speed being evaluated. If not, processing of element  208  is completed and the speed negotiation and testing procedures of  FIG. 2  above resume processing. Otherwise, element  302  is next operable to configure a next set or combination of SAS speed options to permit testing of the present SAS speed using another combination or set of speed options. As is generally known in the art, speed options for such a SAS link may include, for example, the link rate as well as the logical link rate and the spread spectrum clock rates and clocking types available for communication at the current SAS speed. These and other speed options are set by operation of element  302  prior to testing performed by element  304 . 
     Element  304  is then operable to test the SAS link utilizing the current SAS speed and the current set of configured SAS speed options. In general, testing of element  304  may comprise generation and transmission of one or more SCSI requests from the master device directed to the other SAS device. Element  304  further comprises receiving and evaluating any response to the SCSI request. Based in part on the particular SCSI request and response received, if any, element  304  may determine success or failure of the SAS link as presently configured between the master SAS device and the other SAS device coupled thereto. 
     In one exemplary embodiment, the SCSI requests generated and transmitted by operation of element  304  may be non-destructive SCSI requests that will not negatively impact or modify any data stored on the other SAS device. Exemplary of such non-destructive SAS SCSI requests are, test unit ready, inquiry, read buffer, etc. Where the other SAS device is a device that does not risk the loss of stored data, other SCSI requests may be utilized as a matter of design choice without risk of loss of data. 
     In addition to determining success or failure of the SCSI request based on the SCSI request and the associated SCSI response, if any, element  306  further may determine success or failure of the test by evaluating how many if any PHY layer errors occurred during the performance of the SCSI exchange. In accordance with features and aspects hereof, counters or other indicia associated with PHY layer processing may identify and/or count the number of PHY layer errors that occurred during the SCSI request/response exchange. Exemplary of such PHY layer errors are 8b10b encoding errors, symbol errors, parity errors, DWORD synchronization errors, etc. Detection of such errors is generally known to those of ordinary skill in the art. If no PHY layer errors are detected, element  308  determines whether the SCSI request and associated response generated by testing of element  304  were otherwise processed correctly. 
     If no errors are detected during the testing of elements  304  through  308 , element  310  is operable to store indicia of success for this present SAS speed and the presently configured set of speed options. Alternatively, if errors are detected in the processing of elements  304  through  308 , element  312  is operable to store indicia of failure for this current SAS speed using this particular presently configured set of speed options. Following processing of the elements  310  or  312  to store appropriate success/failure indicia, processing continues looping back to element  300  to evaluate more sets of configured speed options for the present SAS speed. 
       FIG. 4  is a flowchart describing another exemplary method in accordance with features and aspects hereof for testing a SAS link as an aspect of the speed negotiation processing between a master SAS device and an associated other SAS device. The method of  FIG. 4  generally comprises iteratively testing one or more sets of configured speed options for each SAS speed supported by the master SAS device performing the negotiation process. In particular, elements  406  through  410  are performed for each set of speed options for each of the supported speeds of the master device. In general, these steps configure a next set of speed options to be utilized when participating in a speed negotiation window between the master SAS device and the other SAS device couple thereto. Next, the repeated steps perform a speed negotiation process generally in accordance with the SAS-2 specifications but enhanced to include testing of one or more configured sets of speed options at the current SAS speed to determine success or failure of the mutually supported SAS speed. Lastly, the repeated steps include storing indicia of success or failure of the speed negotiation and testing process for the current SAS speed at the currently configured set of speed options. These steps are then repeated for each combination of speed options and all supported SAS speeds until all mutually supported SAS speeds have been negotiated, tested, and test results appropriately stored for subsequent utilization. 
     More specifically, element  400  is operable to determine whether additional SAS speeds supported by the master SAS device remain to be negotiated and tested. If not, element  412  is operable to start or continue normal operation of the SAS device including, for example, selecting one of the tested, mutually supported SAS speeds. If more SAS speeds remain to be evaluated, element  402  is operable to select a next SAS speed to be utilized in performing speed negotiation and associated testing. Element  404  is then operable to determine whether additional sets of speed options remain to be tested at the currently selected SAS speed. If not, processing continues looping back to element  400  until all SAS speeds and all associated speed option settings have been negotiated and tested. 
     For the currently configured set of speed options and the currently selected SAS speed, elements  406  through  410  are operable as noted above to configure the speed options, participate in the speed negotiation window and associated testing, and to store indicia of success or failure for the current selected SAS speed with the currently configured set of speed options. Specifically, element  406  configures the next set of speed options for the currently selected SAS speed. Exemplary speed options may be as exemplified above and as appropriate for the particular application. Element  408  then participates in SAS speed negotiation window processing generally in accordance with the SAS-2 specifications. Further, element  408  is operable as enhanced by features and aspects hereof to test a SAS speed determined to be mutually supported by both the master device and the other SAS device coupled thereto. As noted above, the testing may comprise generating and transmitting SCSI requests from the master device to the other SAS device coupled thereto. In one exemplary embodiment where the other SAS device may store user supplied data, the particular SCSI commands sent for purposes of testing may be non-destructive of such user data. For example, SCSI inquiry, testing unit ready, and read buffer commands may be utilized to test the link between the master device and other SAS device without risk of destroying any user data stored in the other SAS device. Element  408  therefore generates and transmits an appropriate SCSI request and receives the response therefrom. 
     Based on the SCSI response and potentially other indicia of success or failure of the transmitted request and response, element  410  is then operable to store appropriate indicia of success or failure determined from the testing process for the currently selected SAS speed with the currently configured set of speed options. In general, the stored indicia may be stored in any suitable memory or register structure within the master SAS device such that the particular SAS speed and particular configured set of speed options are identified along with the results of the testing process for that configured speed and set of options. Such a table or register structure may then be utilized by an administrative user or process to permit manual or automated selection of a preferred or optimal SAS speed for the particular application and the particular environment. Following processing of elements  406  through  410 , processing continues looping back to element  404  to determine whether additional sets of speed options need to be configured and tested. 
     As noted above, determination of success or failure of the testing performed by element  408  may include correct receipt of a SCSI response generated by the other SAS device in response to the SCSI request as well as monitoring of any PHY layer errors occurring during the SCSI exchange. The PHY layer may therefore include suitable indicia or counters to indicate occurrence of particular errors in the SCSI request/response exchange. 
       FIG. 5  is a flowchart providing exemplary additional details of the processing of element  406  of  FIG. 4  to configure a next set of speed options prior to testing the link as presently configured. In advance of the testing of a particular set of speed options for a particular SAS speed, a PHY reset sequence is performed to permit initiation of the next speed negotiation window with a newly configured set of speed options. By so cycling the status of the link, the other SAS device will be prepared to perform a speed negotiation process again in response to the speed negotiation performed by the master SAS device and to respond to test commands in accordance with features and aspects hereof. Element  500  is thus operable to perform a PHY reset sequence in preparation for a new speed negotiation process. Elements  502  through  508  are then operable to configure each of the settings for the next set of speed options to be tested by operation of the method discussed above with respect to  FIG. 4 . Specifically, element  502  configures the link speed option of the current set of options, element  504  configures the spread spectrum clocking of the current set of speed options, element  506  configures the type of spread spectrum clocking of the set of speed options, and element  508  configures the logical link speed (used for SAS-2 multiplexing of a link) of the current set of speed options. 
     Those of ordinary skill in the art will readily recognize numerous additional and equivalent method steps associated with the processing of the methods of  FIGS. 2 through 5  above. Such additional and equivalent steps are eliminated here simply for brevity of this discussion. In addition, those of ordinary skill in the art will readily recognize standard processing within a SAS device to utilize a list of mutually supported, tested SAS speeds for purposes of selecting a preferred or optimal SAS speed for the particular link in the particular application. 
     While the invention has been illustrated and described in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character. One embodiment of the invention and minor variants thereof have been shown and described. Protection is desired for all changes and modifications that come within the spirit of the invention. Those skilled in the art will appreciate variations of the above-described embodiments that fall within the scope of the invention. As a result, the invention is not limited to the specific examples and illustrations discussed above, but only by the following claims and their equivalents.